Epoxyeicosatrienoic acid prevents postischemic electrocardiogram abnormalities in an isolated heart model

Cytochrome P450 epoxygenases metabolize arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) which are in turn converted to dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH). The main objective of this study was to investigate the protective effects of EETs following ischemic injury using an ex vivo electrocardiogram (EKG) model. Hearts from C57Bl/6, transgenic mice with cardiomyocyte-specific overexpression of CYP2J2 (Tr) and wildtype (WT) littermates were excised and perfused with constant pressure in a Langendorff apparatus. Electrodes were placed superficially at the right atrium and left ventricle to assess EKG waveforms. In ischemic reperfusion experiments hearts were subjected to 20 min of global no-flow ischemia followed by 20 min of reperfusion (R20). The EKG from C57Bl/6 hearts perfused with 1 μM 14,15-EET showed less QT prolongation (QTc) and ST elevation (STE) (QTc = 41 ± 3, STE = 2.3 ± 0.3; R20: QTc = 42 ± 2 ms, STE = 1.2 ± 0.2mv) than control hearts (QTc = 36 ± 2, STE = 2.3 ± 0.2; R20: QTc = 53 ± 3 ms; STE = 3.6 ± 0.4mv). Similar results of reduced QT prolongation and ST elevation were observed in EKG recording from CYP2J2 Tr mice (QTc = 35 ± 1, STE = 1.9 ± 0.1; R20: QTc = 38 ± 4 ms, STE = 1.3 ± 0.2mv) compared to WT hearts. The putative epoxygenase inhibitor MS-PPOH (50 μM) and EET antagonist 14,15-EEZE (10 μM) both abolished the cardioprotective response, implicating EETs in this process. In addition, separate exposure to the K_ATP channel blockers glibenclamide (1 μM) and HMR1098 (10 μM), or the PKA protein inhibitor H89 (50 nM) during reperfusion abolished the improved repolarization in both the models. Consistent with a role of PKA, CYP2J2 Tr mice had an enhanced activation of the PKAα regulatory II subunit in plasma membrane following IR injury. The present data demonstrate that EETs can enhance the recovery of ventricular repolarization following ischemia, potentially by facilitating activation of K⁺ channels and PKA-dependent signaling.     

Cardioprotection following adenosine kinase inhibition in rat hearts

Adenosine kinase phosphorylates adenosine to AMP, the primary pathway for adenosine metabolism under basal conditions. Inhibition of adenosine kinase results in a site–specific increase in interstitial adenosine. Using a rat model of myocardial infarction, we examined the protective effects of adenosine kinase inhibition. Male Sprague–Dawley rats underwent 30 min regional occlusion followed by 90 min reperfusion. Infarct size, expressed as a percent of the area–at–risk, IS/AAR(%), was 58.0 ± 2.1 % in untreated rats. Pretreatment with the adenosine kinase inhibitor, 5–iodotubercidin (1 mg/kg), limited infarct development to 37.5±3.7% (P < 0.001). The A₁ adenosine receptor (A₁AR) antagonist, DPCPX (100 µg/kg), abolished the infarct–sparing effect of 5–iodotubercidin (IS, 62.8 ± 1.3%). Similarly, the A₃ adenosine receptor (A₃AR) antagonist, MRS–1523 (2 mg/kg), and the δ–opioid receptor (DOR) antagonist, BNTX, (1 mg/kg) abolished the reduction of IS produced by iodotubercidin. Pretreatment with the ROS scavenger, 2–MPG (20 mg/kg), or the PKC–δ antagonist, rottlerin (0.3 mg/kg) also abolished iodotubercidin–mediated cardioprotection. Furthermore, pretreatment with 5–HD, a mitochondrial K_ATP (mitoK_ATP) channel inhibitor, but not the sarcolemmal K_ATP channel blocker, HMR–1098, abrogated the beneficial effects of adenosine kinase inhibition (IS, 59.5 ± 3.8%). These data suggest that inhibition of adenosine kinase is effective in reducing infarct development via A₁AR, A₃AR and DOR activation. Data also suggest that this protection is mediated via ROS, PKC–δ and mitoK_ATP channels.     

牛磺酸对外源性羟自由基诱导心肌细胞凋亡的影响

目的：观察牛磺酸对外源性羟自由基诱导心肌细胞凋亡的影响。方法：采用培养的第2代心肌细胞，随机分面4组：（1）正常对照组：仅用DMEM培养；（2）羟自由基组：OH－终浓度为0．1mmol.L^-1；（3）牛左酸组：牛磺酸终浓度为30mmol.L^-1；（4）牛磺酸＋羟自由基组：牛磺酸30mmol.L^-1 OH-0.1mmol.L。观察心肌细胞存活率和形态学，流式细胞仪双标法检测细胞凋亡率。结果：（1）羟自由基组心肌细胞存活率降低，和对照组比较有显性差异（P＜0．05），牛磺酸＋羟自由基组细胞存活率较羟自由基组高（P＜0．05），（2）Annexin V /PI-细胞即凋亡细胞在羟自由基组有较高的发生率，明显高于其他各组（P＜0．05）；牛磺酸＋羟自由基组的细胞凋亡率显低于羟自由基组（P＜0．05），（3）羟自由基组凋亡心肌细胞呈特征性超微结构。结论：牛磺酸能减轻外源性羟自由基诱导的心肌细胞凋亡。     

Mechanisms of cardioprotective effects of magnesium on hypoxia-reoxygenation-induced injury

During cardiac ischemia or hypoxia, increased levels of extracellular Mg show cardioprotective effects. The mechanisms of high level Mg-induced cardioprotection were examined in Langendorff perfused rat hearts. In the control group (1.2 mM Mg during hypoxia), the recovery of the left ventricular developed pressure (LVDP) after 30 min of reoxygenation was 57.6±3.0% of the level observed before hypoxia. In the high Mg group (12 mM Mg during hypoxia), the time course of recovery was faster than in the control group; the recovery level of LVDP improved to 78.4±4.2%. This protective effect of high levels of Mg decreased to 69.0±3.6% with the application of 5-hydroxydecanoic acid (100 μM), a specific mitochondrial ATP-sensitive potassium channel (K_ATP) blocker. In the low Ca group (0.2 mM Ca during hypoxia), the recovery of LVDP did not reach the level observed in the high Mg group (64.7±5.9%), but with application of diazoxide, a specific mitochondrial K_ATP channel opener, the LVDP recovery improved to 81.8±11.1%, similar to the level observed in the high Mg group. These results suggest that cardioprotective effects of high levels of extracellular Mg during hypoxia occur not only due to energy conservation and/or by intracellular prevention of Ca²⁺ over-load, but also by opening of the mitochondrial K_ATP channel.     

Glucose regulates the effects of leptin on hypothalamic POMC neurons

Leptin is believed to exert its potent appetite-suppressing effects via stimulation of hypothalamic anorexigenic proopiomelanocortin (POMC)-containing neurons and inhibition of orexigenic agouti-related protein (AgRP) neurons. We show here that at 11 mM glucose leptin excites POMC cells. At 5 mM glucose, however, leptin hyperpolarizes POMC neurons and suppresses action potential firing, by producing a greater decrease in excitatory synaptic tone than inhibitory tone. These results argue that when glucose is low (5 mM or less) AgRP neurons will be more important for mediating the anorectic effects of leptin than POMC cells. However, at high glucose concentrations (11 mM), activation of POMC cells may contribute to the appetite-suppressing effects of leptin. Our data also suggest the regulation of neuropeptide efficacy as a novel function of hypothalamic glucose sensing.     

Thiazolidinedione drugs block cardiac K<Subscript>ATP</Subscript> channels and may increase propensity for ischaemic ventricular fibrillation in pigs

Aims/hypothesis Opening of ATP-sensitive potassium (K_ATP) channels during myocardial ischaemia shortens action potential duration and is believed to be an adaptive, energy-sparing response. Thiazolidinedione drugs block K_ATP channels in non-cardiac cells in vitro. This study determined whether thiazolidinedione drugs block cardiac K_ATP channels in vivo. Methods Experiments in 68 anaesthetised pigs determined: (1) effects of inert vehicle, troglitazone (10 mg/kg i.v.) or rosiglitazone (0.1 or 1.0 mg/kg i.v.) on epicardial monophasic action potential (MAP) during 90 min low-flow ischaemia; (2) effects of troglitazone, rosiglitazone or pioglitazone (1 mg/kg i.v.) on response of MAP to intracoronary infusion of a K_ATP channel opener, levcromakalim; and (3) effects of inert vehicle, rosiglitazone (1 mg/kg i.v.) or the sarcolemmal K_ATP blocker HMR-1098 on time to onset of ventricular fibrillation following complete coronary occlusion. Results With vehicle, epicardial MAP shortened by 44 ± 9 ms during ischaemia. This effect was attenuated to 12 ± 8 ms with troglitazone and 6 ± 6 ms with rosiglitazone (p < 0.01 for both vs vehicle), suggesting K_ATP blockade. Intracoronary levcromakalim shortened MAP by 38 ± 10 ms, an effect attenuated to 12 ± 8, 13 ± 4 and 9 ± 5 ms during co-treatment with troglitazone, rosiglitazone or pioglitazone (p < 0.05 for each), confirming K_ATP blockade. During coronary occlusion, median time to ventricular fibrillation was 29 min in pigs treated with vehicle and 6 min in pigs treated with rosiglitazone or HMR-1098 (p < 0.05 for both vs vehicle), indicating that K_ATP blockade promotes ischaemic ventricular fibrillation in this model. Conclusions/interpretation Thiazolidinedione drugs block cardiac K_ATP channels at clinically relevant doses and promote onset of ventricular fibrillation during severe ischaemia.     

Effect of the Cardioselective, Sarcolemmal KATP Channel Blocker HMR 1098 on Atrial Electrical Remodeling During Pacing-Induced Atrial Fibrillation in Dogs

PURPOSE: The progressive shortening of the atrial effective refractory period (ERP) during atrial fibrillation (AF) might be due to the activation of the KATP channels by rapid atrial rates. We tested the hypothesis that the cardioselective, sarcolemmal KATP channel blocker HMR 1098 would prevent atrial ERP shortening during AF. METHODS AND RESULTS: Nine dogs were treated with HMR 1098 (3 mg/kg bolus injection followed by a continuous intravenous (i.v.) infusion at 17 microg/kg/min rate maintained throughout the study) and 7 dogs served as controls receiving i.v. saline. Pharmacological autonomic blockade was induced by i.v. administration of atropine (0.04 mg/kg) and propranolol (0.2 mg/kg) and maintained throughout the study by continuous i.v. infusion of atropine (0.007 mg/kg/h) and propranolol (0.04 mg/kg/h). Rapid right atrial pacing at 50 msec cycle length (CL) was initiated and maintained for 6 hours. High right atrial ERP (HRA-ERP) and corrected sinus node recovery time (HRA-cSNRT), coronary sinus ERP (CS-ERP) and corrected SNRT (CS-cSNRT) at three (400, 300, 200 msec) CLs were measured before and after pacing at different time points. Baseline values were not different between control and treated dogs. In the control group the HRA-ERP progressively shortened (from 179 +/- 21 msec at baseline to 161 +/- 23 msec at 360 min at 400 msec CL) ( p = 0.002), with a gradual decrease, loss or inversion of ERP rate adaptation at shorter (300, 200 msec) CLs. HMR 1098 treatment did not prevent the shortening of HRA-ERP during the first 2 to 3 hours of rapid atrial pacing. However, beginning at 180-240 min, HMR 1098 increased the HRA-ERP ( p = 0.01) to baseline by 360 min. HMR 1098 treatment did not prevent another feature of atrial electrical remodeling, the flattening or inversion of ERP rate adaptation. In neither group did CS-ERP shortening occur. The maximum cSNRT at 360 min prolonged significantly in both groups during HRA and CS pacing as well compared with baseline. CONCLUSIONS: HMR 1098 treatment did not prevent the shortening of HRA-ERP, the salient feature of atrial electrical remodeling in the first 2 to 3 hours of rapid atrial rates, but did prevent it thereafter. Another characteristic feature of atrial electrical remodeling, the flattening or inversion of physiological ERP rate adaptation was not prevented by HMR 1098 treatment. Sinus node depression was detectable after short-term (6 hours) rapid atrial pacing and was not affected by HMR 1098.     

Pretreatment with Sarafotoxin 6c Prior to Coronary Occlusion Protects Against Infarction and Arrhythmias via Cardiomyocyte Mitochondrial K<Subscript>ATP</Subscript> Channel Activation in the Intact Rabbit Heart During Ischemia/Reperfusion

Background Endothelial ET_B receptor activation by exogenously administered sarafotoxin 6c(a snake venom peptide with a sequence homology to ET-1 prior to ischemia activates release of nitric oxide(NO) and previous studies have shown that NO facilitates mitochondrial K_ATP activation in cardiac cells and cardioprotection. Objectives and methods The aim of this investigation was to test whether the administration of sarafotoxin 6c(a selective ET_B receptor agonist) has cardioprotective and antiarrhythmic effects against ischemia and reperfusion injury in a well-standardized model of reperfusion arrhythmias in anesthetized adult male rabbits (n = 53) subjected to 30 min occlusion of the left coronary artery followed by 120 min of reperfusion. Results Pretreatment with sarafotoxin 6c (0.24 nmol/kg, i.v.) prior to the period of coronary occlusion offers significant infarct size reduction (19.1 ± 2.0% versus 39.7 ± 3.7% in the saline control group; P < 0.01) and antiarrhythmic effects. Sarafotoxin 6c treatment significantly attenuated the incidence of life-threatening arrhythmias like sustained VT (13 versus 100% in the saline control group; P < 0.005) and other arrhythmias (25 versus 100% in the saline control group; P < 0.005), and increased the number of surviving animals without arrhythmias. Pretreatment with 5-HD but not HMR 1883 abolished the beneficial effects of sarafotoxin 6c on reperfusion induced arrhythmias and cardioprotection suggesting that benefits have been achieved via the selective activation of cardiomyocyte mitochondrial K_ATP channels. Sarafotoxin 6c evoked NO release and selective activation of mitoK_ATP channels in cardiomyocytes contributes to cardioprotection and antiarrhythmic activity during ischemia-reperfusion in the anesthetized rabbit. Conclusions We conclude that the selective activation of ET_B receptors by sarafotoxin 6c prior to coronary occlusion contributes to cardioprotective and antiarrhythmic properties.     

Size and Shape’s Effects on the High-Pressure Behavior of WS2 Nanomaterials

Exploring the behavior of nanocrystals with varying shapes and sizes under high pressure is crucial to understanding the relationship between the morphology and properties of nanomaterials. In this study, we investigated the compression behaviors of WS₂ nanotubes (NT-WS₂) and fullerene-like nanoparticles (IF-WS₂) by in situ high-pressure X-ray diffraction (XRD) and Raman spectroscopy. It was found that the bulk modulus of NT-WS₂ is 81.7 GPa, which is approximately twice as large as that of IF-WS₂ (46.3 GPa). This might be attributed to the fact that IF-WS₂ with larger d-spacing along the c-axis and higher defect density are more compressible under isotropic pressure than NT-WS₂. Thus, the slender NT-WS₂ possess a more stable crystal structure than the IF-WS₂. Our findings reveal that the effects of morphology and size play crucial roles in determining the high-pressure properties of WS₂ nanoparticles, and provide significant insight into the relationship between structure and properties.     

Essential role of the imidazoline moiety in the insulinotropic effect but not the KATP channel-blocking effect of imidazolines; a comparison of the effects of efaroxan and its imidazole analogue, KU14R

Aims/hypothesis Imidazolines are a class of investigational antidiabetic drugs. It is still unclear whether the imidazoline ring is decisive for insulinotropic characteristics. Materials and methods We studied the imidazoline efaroxan and its imidazole analogue, KU14R, which is currently classified as an imidazoline antagonist. The effects of both on stimulus secretion-coupling in normal mouse islets and beta cells were compared by measuring K_ATP channel activity, plasma membrane potential, cytosolic calcium concentration ([Ca²⁺]_c) and dynamic insulin secretion. Results In the presence of 10 mmol/l but not of 5 mmol/l glucose, efaroxan (100 μmol/l) strongly enhanced insulin secretion by freshly isolated perifused islets, whereas KU14R (30, 100 or 300 μmol/l) was ineffective at both glucose concentrations. Surprisingly, the insulinotropic effect of efaroxan was not antagonised by KU14R. K_ATP channels were blocked by efaroxan (IC₅₀ 8.8 μmol/l, Hill slope −1.1) and by KU14R (IC₅₀ 31.9 μmol/l, Hill slope −1.5). Neither the K_ATP channel-blocking effect nor the depolarising effect of efaroxan was antagonised by KU14R. Rather, both compounds strongly depolarised the beta cell membrane potential and induced action potential spiking. However, KU14R was clearly less efficient than efaroxan in raising [Ca²⁺]_c in single beta cells and whole islets at 5 mmol/l glucose. The increase in [Ca²⁺]_c induced by 10 mmol/l glucose was affected neither by efaroxan nor by KU14R. Again, KU14R did not antagonise the effects of efaroxan. Conclusions/interpretation The presence of an imidazole instead of an imidazoline ring leads to virtually complete loss of the insulinotropic effect in spite of a preserved ability to block K_ATP channels. The imidazole compound is less efficient in raising [Ca²⁺]_c; in particular, it lacks the ability of the imidazoline to potentiate the enhancing effect of energy metabolism on Ca²⁺-induced insulin secretion.     

Inhibition of phenylephrine induced hypertrophy in rat neonatal cardiomyocytes by the mitochondrial KATP channel opener diazoxide

The effect of the putative mitochondrial K(ATP) channel opener diazoxide (100 microM) was studied in terms of its ability to modulate the hypertrophic effect of 24 h treatment with the alpha(1) adrenoceptor agonist phenylephrine (PE; 10 microM) in cultured neonatal rat ventricular myocytes. PE on its own significantly increased cell size by 40%, (3)H leucine incorporation by 37% and produced more than a threefold elevation in both atrial natriuretic peptide and myosin light chain-2 expression. These effects were nearly completely prevented by diazoxide although the inhibitory effect of this agent was generally mitigated by the mitochondrial K(ATP) channel antagonists 5-hydroxydecanoic acid (100 microM) and glibenclamide (50 microM). Although PE produced an early threefold elevation in MAP kinase activation this was generally unaffected by diazoxide. PE also produced a greater than threefold increase in Na-H exchanger isoform 1 (NHE-1) expression which, was prevented by diazoxide treatment. Our study therefore, demonstrates a potential antihypertrophic influence of mitochondrial K(ATP) channel activation which, is related to diminished NHE-1 expression. Mitochondrial K(ATP) channel activation could represent an effective approach to minimize the myocardial hypertrophic process.     

The Reaction Products of the Al–Nb–B2O3–CuO System in an Al 6063 Alloy Melt and Their Influence on the Alloy’s Structure and Characteristics

To meet aero-engine aluminum skirt requirements, an experiment was carried out using Al–Nb–B₂O₃–CuO as the reaction system and a 6063 aluminum alloy melt as the reaction medium for a contact reaction, and 6063 aluminum matrix composites containing in situ particles were prepared with the near-liquid-phase line-casting method after the reaction was completed. The effects of the reactant molar ratio and the preheating temperature on the in situ reaction process and products were explored in order to determine the influence of in situ-reaction-product features on the organization and the qualities of the composites. Thermodynamic calculations, DSC analysis, and experiments revealed that the reaction could continue when the molar ratio of the reactants of Al–Nb–B₂O₃–CuO was 6:1:1:1.5. A kinetic study revealed that the Al thermal reaction in the system produced Al₂O₃ and [B], and the [B] atoms interacted with Nb to generate NbB₂. With increasing temperature, the interaction between the Nb and the AlB₂ produced hexagonal NbB₂ particles with an average longitudinal size of 1 μm and subspherical Al₂O₃ particles with an average longitudinal size of 0.2 μm. The microstructure of the composites was reasonably fine, with an estimated equiaxed crystal size of around 22 μm, a tensile strength of 170 MPa, a yield strength of 135 MPa, an elongation of 13.4%, and a fracture energy of 17.05 × 10⁵ KJ/m³, with a content of 2.3 wt% complex-phase particles. When compared to the matrix alloy without addition, the NbB₂ and Al₂O₃ particles produced by the in situ reaction had a significant refinement effect on the microstructure of the alloy, and the plasticity of the composite in the as-cast state was improved while maintaining higher strength and better overall mechanical properties, allowing for industrial mass production.     

Comparative effects of melatonin, L-deprenyl, Trolox and ascorbate in the suppression of hydroxyl radical formation during dopamine autoxidation in vitro

Degeneration of nigrostriatal dopaminergic neurons is the major pathogenic substrate of Parkinson's disease (PD). Inhibitors of monoamine oxidase B (MAO-B) have been used in the treatment of PD and at least one of them, i.e., deprenyl, also displays antioxidant activity. Dopamine (DA) autoxidation produces reactive oxygen species implicated in the loss of dopaminergic neurons in the nigrostriatal pathway. In this study we compared the effects of melatonin with those of deprenyl and vitamins E and C in preventing the hydroxyl radical (8OH) generation during DA oxidation. The rate of production of 2,3-dihydroxybenzoate (2,3-DHBA) in the presence of salicylate, an *OH scavenger, was used to detect the in vitro generation of *OH during iron-catalyzed oxidation of DA. The results showed a dose-dependent effect of melatonin, deprenyl and vitamin E in counteracting DA autoxidation, whereas vitamin C had no effect. Comparative analyses between the effect of these antioxidants showed that the protective effect of melatonin against DA autoxidation was significantly higher than that of the other compounds tested. Also, when melatonin plus deprenyl were added to the incubation medium, a potentiation of the antioxidant effect was found. These findings suggest that antioxidants may be useful in brain protection against toxicity of reactive oxygen species produced during DA oxidation, and melatonin, alone or in combination with deprenyl, may be an important component of the brain's antioxidant defenses to protect it from dopaminergic neurodegeneration.     

Effects of K(ATP) channel openers, P-1075, pinacidil, and diazoxide, on energetics and contractile function in isolated rat hearts

We investigated the metabolic effects of a potent opener of ATP-sensitive K(+) (K(ATP)) channels, P-1075, in perfused rat hearts with the help of(31)P NMR spectroscopy. A 20 min infusion of 5 microm P-1075 depleted phosphocreatine and ATP by approximately 40%, concomitantly with a two-fold increase in inorganic phosphate, while oxygen consumption by the hearts increased by 50%. P-1075 induced a cardiac contracture (left ventricular end diastolic pressure increased from 6 to 60 mmHg) and a cardiac arrest after an infusion of approximately 9 min. The effects were fully reversed by glibenclamide (5 microm), but not by sodium 5-hydroxydecanoate (0.4 m m). A P-1075-related K(ATP) opener, pinacidil (0.3 m m), partially reversed the effects of P-1075, but a structurally unrelated opener, diazoxide (0.5 m m), had no effect. Pinacidil and diazoxide alone did not significantly affect PCr and ATP levels. Bioenergetic and functional effects similar to those of P-1075 were induced by infusion of a classic mitochondrial uncoupler, 2,4-dinitrophenol (50 microm); however, they were not abolished by glibenclamide. In addition, it was shown, using(87)Rb NMR, that both agents, P-1075 and 2,4-dinitrophenol, resulted in a stimulation of Rb(+) efflux from the Rb(+) loaded rat hearts by approximately 130 and 65%, respectively, in a glibenclamide-sensitive manner. An inhibitory effect of P-1075 on ATP synthesis cannot be explained by its well-known action on sarcolemmal K(ATP) channels. We concluded that, unlike an uncoupling effect of 2,4-dinitrophenol, an inhibitory effect of P-1075 is produced by uncoupling of oxidative phosphorylation through the activation of mitochondrial K(ATP) channels.     

A Kir6.2 mutation causing severe functional effects in vitro produces neonatal diabetes without the expected neurological complications

Aims/hypothesis Heterozygous activating mutations in the pancreatic ATP-sensitive K⁺ channel cause permanent neonatal diabetes mellitus (PNDM). This results from a decrease in the ability of ATP to close the channel, which thereby suppresses insulin secretion. PNDM mutations that cause a severe reduction in ATP inhibition may produce additional symptoms such as developmental delay and epilepsy. We identified a heterozygous mutation (L164P) in the pore-forming (Kir6.2) subunit of the channel in three unrelated patients and examined its functional effects. Methods The patients (currently aged 2, 8 and 20 years) developed diabetes shortly after birth. The two younger patients attempted transfer to sulfonylurea therapy but were unsuccessful (up to 1.1 mg kg⁻¹ day⁻¹). They remain insulin dependent. None of the patients displayed neurological symptoms. Functional properties of wild-type and mutant channels were examined by electrophysiology in Xenopus oocytes. Results Heterozygous (het) and homozygous L164P K_ATP channels showed a marked reduction in channel inhibition by ATP. Consistent with its predicted location within the pore, L164P enhanced the channel open state, which explains the reduction in ATP sensitivity. HetL164P currents exhibited greatly increased whole-cell currents that were unaffected by sulfonylureas. This explains the inability of sulfonylureas to ameliorate the diabetes of affected patients. Conclusions/interpretation Our results provide the first demonstration that mutations such as L164P, which produce a severe reduction in ATP sensitivity, do not inevitably cause developmental delay or neurological problems. However, the neonatal diabetes of these patients is unresponsive to sulfonylurea therapy. Functional analysis of PNDM mutations can predict the sulfonylurea response. P. Tammaro and S. E. Flanagan contributed equally to this study.     

Effect of the Ca2Mg6Zn3 Phase on the Corrosion Behavior of Biodegradable Mg-4.0Zn-0.2Mn-xCa Alloys in Hank’s Solution

The effect of the Ca₂Mg₆Zn₃ phase on the corrosion behavior of biodegradable Mg-4.0Zn-0.2Mn-xCa (ZM-xCa, x = 0.1, 0.3, 0.5 and 1.0 wt.%) alloys in Hank’s solution was investigated with respect to phase spacing, morphology, distribution and volume fraction. With the increase in Ca addition, the volume fraction of the Ca₂Mg₆Zn₃ phase increased from 2.5% to 7.6%, while its spacing declined monotonically from 43 μm to 30 μm. The Volta potentials of secondary phases relative to the Mg matrix were measured by using scanning kelvin probe force microscopy (SKPFM). The results show that the Volta potential of the intragranular spherical Ca₂Mg₆Zn₃ phase (+109 mV) was higher than that of the dendritic Ca₂Mg₆Zn₃ phase (+80 mV). It is suggested that the Ca₂Mg₆Zn₃ acted as a cathode to accelerate the corrosion process due to the micro-galvanic effect. The corrosion preferred to occur around the spherical Ca₂Mg₆Zn₃ phase at the early stage and developed into the intragranular region. The corrosion rate increased slightly with increasing Ca content from 0.1 wt.% to 0.5 wt.% because of the enhanced micro-galvanic corrosion effect. The decrease in the phase spacing and sharp increase in the secondary phase content resulted in a dramatic increase in the corrosion rate of the ZM-1.0Ca alloy.     

Transgenic upregulation of I<Subscript>K1</Subscript> in the mouse heart is proarrhythmic

The role of the cardiac current I_k1 in arrhythmogenesis remains highly controversal. To gain further insights into the mechanisms of I_K1 involvement in cardiac excitability, we studied the susceptibility of transgenic mice with altered I_K1 to arrhythmia during various pharmacological and physiological challenges. Arrhythmogenesis was studied in transgenic mice expressing either dominant negative Kir2.1-AAA or wild type Kir2.1 subunits in the heart, models of I_K1 suppression (AAA-TG) and up-regulation (WT-TG), respectively. Under normal conditions, both anesthetized wild type (WT) and AAA-TG mice did not display any spontaneous arrhythmias. In contrast,WT-TG mice displayed numerous arrhythmias of various types. In isolated hearts, the threshold concentration for halothane-induced ventricular tachycardias (VT) was increased to 170 % in the AAA-TG and decreased to 55 % in WT-TG hearts when compared to WT hearts. The number of PVCs induced by AV node ablation combined with hypokalemia was reduced in AAA-TG hearts and increased in WT-TG mice. After AV node ablation AAA-TG hearts were more tolerant, and WT-TG less tolerant to isoproterenol- induced arrhythmias than WT hearts. Analysis of monophasic action potentials in isolated hearts shows a significant reduction in the dispersion of action potential repolarization in mice with suppressed I_K1. The data strongly support the hypothesis that in the mouse heart upregulation of I_K1 is proarrhythmic, and that under certain conditions I_K1 blockade in cardiac myocytes may be a potentially useful antiarrhythmic strategy. When we published the article Piao L et al (2007) Transgenic upregulation of I_K1 in the mouse heart is proarrhythmic. Basic Res Cardiol 102:412–428 [ the online version can be found at] some corrections by the author had erroneously not been carried out before publication: 1) In the abstract, the sixth sentence should read In isolated hearts, the threshold concentration for halothane-induced ventricular tachycardias (VT) was increased to 167% in the AAA-TG and decreased to 54% in WT-TG hearts when compared to WT hearts. 2) The Acknowledgement was accidentally omitted: Acknowledgement The authors thank Dr. Louis D'Alecy for telemetric ECG recordings. 3) Reference 32 should be replaced with the following 32. Noujaim SF, Pandit SV, Berenfeld O, Vikstrom K, Cerrone M, Mironov S, Zugermayr M, Lopatin AN, Jalife J (2007) Up-regulation of the inward rectifier K⁺ current (I_K1) in the mouse heart accelerates and stabilizes rotors. J Physiol 578:315–326 The publisher apologises for any inconvenience caused by this mistakes. This study was supported by RO1 HL69052 grant from NHBLI (AL). Part of this work was presented at the AHA Scientific Sessions 2003: Li J.,McLerie M. and Lopatin A. N. Transgenic Regulation of IK1 in the Mouse Heart Strongly Affects Drug-Induced Arrhythmias. Circulation 2003; 108(17): P. IV-87; Pos. 410. *Both authors contributed equally to the work.     

From the Cover: Magmatic thickening of crust in non–plate tectonic settings initiated the subaerial rise of Earth’s first continents 3.3 to 3.2 billion years ago

When and how Earth''s earliest continents—the cratons—first emerged above the oceans (i.e., emersion) remain uncertain. Here, we analyze a craton-wide record of Paleo-to-Mesoarchean granitoid magmatism and terrestrial to shallow-marine sedimentation preserved in the Singhbhum Craton (India) and combine the results with isostatic modeling to examine the timing and mechanism of one of the earliest episodes of large-scale continental emersion on Earth. Detrital zircon U-Pb(-Hf) data constrain the timing of terrestrial to shallow-marine sedimentation on the Singhbhum Craton, which resolves the timing of craton-wide emersion. Time-integrated petrogenetic modeling of the granitoids quantifies the progressive changes in the cratonic crustal thickness and composition and the pressure–temperature conditions of granitoid magmatism, which elucidates the underlying mechanism and tectonic setting of emersion. The results show that the entire Singhbhum Craton became subaerial ∼3.3 to 3.2 billion years ago (Ga) due to progressive crustal maturation and thickening driven by voluminous granitoid magmatism within a plateau-like setting. A similar sedimentary–magmatic evolution also accompanied the early (>3 Ga) emersion of other cratons (e.g., Kaapvaal Craton). Therefore, we propose that the emersion of Earth’s earliest continents began during the late Paleoarchean to early Mesoarchean and was driven by the isostatic rise of their magmatically thickened (∼50 km thick), buoyant, silica-rich crust. The inferred plateau-like tectonic settings suggest that subduction collision–driven compressional orogenesis was not essential in driving continental emersion, at least before the Neoarchean. We further surmise that this early emersion of cratons could be responsible for the transient and localized episodes of atmospheric–oceanic oxygenation (O₂-whiffs) and glaciation on Archean Earth.

The emergence of continental crust above sea level (called continental emersion) critically influences atmospheric and ocean chemistry, climate, and the supply of nutrients to the oceans via weathering and fluvial runoff (1, 2). However, it remains unclear when large areas of subaerial continental crust first appeared on Earth (1–13). A rapid and extensive emersion of continental crust at the Archean–Proterozoic transition (2.5 billion years ago [Ga]) is inferred from abrupt shifts in the oxygen isotope compositions of shales and magmatic zircons, zinc isotope composition of iron formations, and an increase in subaerial continental volcanism at that time (1, 3–5, 7). However, >3.0 to 2.7-Ga-old paleosols (ancient horizons of subaerial weathering) and terrestrial sedimentary rocks that formed atop Earth''s earliest stable continental nuclei, the cratons (14–17), provide direct evidence for earlier episodes of continental emersion. This inference is further corroborated by an increase in the diversity of detrital zircon ages in clastic sedimentary rocks from ∼2.8 Ga onwards, representing the development of regionally extensive watersheds at that time (13). Thus, subaerial exposure of continental crust before 2.5 Ga seems evident. However, the exact timing and spatial extent of these emersion events are poorly constrained, and their global significance remains unclear. Moreover, the mechanisms and tectonic settings that drove continental emersion during the Archean also remain ambiguous. A uniformitarian view posits that Archean continental emersion (whether at ∼2.5 Ga or earlier) was driven by plate tectonics (1, 7, 9) with subduction-collision processes forming thick continental crust with high-standing topography via magmatism and compressional deformation, as is observed on modern Earth (2). However, the operation of plate tectonics in the Archean is disputed (9, 10, 18, 19), and a growing body of evidence suggests that subduction-collision processes were not globally prevalent until ∼2.5 to 2.0 Ga (10, 20–25), warranting the consideration of alternative mechanisms for producing subaerial continental landmasses on early Earth.Here, we integrate the Paleoarchean (3.6 to 3.2 Ga) to Mesoarchean (3.2 to 2.8 Ga) magmatic and sedimentary records of the Singhbhum Craton of India to elucidate the timing and underlying geodynamics of craton-wide emersion of continental crust in the Archean. This craton is ideal for studying Archean continental emersion as it hosts widespread Mesoarchean terrestrial to shallow-marine siliciclastic strata (26–29) and one of the oldest paleosols on Earth (the ∼3.29- to 3.08-Ga Keonjhar paleosol) (30) (Fig. 1A), providing an unambiguous record of early subaerial continental crust. We first synthesize detrital zircon data (SI Appendix, Methods and Datasets S1 and S2) from these Mesoarchean strata to determine the timing of emersion of the Singhbhum Craton. Then, we analyze the published compositional data of the craton’s Paleo-to-Mesoarchean granitoids (SI Appendix, Methods and Dataset S3) to reconstruct the history of crustal thickening and chemical maturation before and during the emersion. This allows us to link the physicochemical evolution of Archean cratonic crust to its emersion as the long-term topography of subaerial continents is critically controlled by their thick, silica-rich (less-dense) crust, which experiences large positive buoyancy and thereby a greater isostatic uplift relative to the surrounding thin and mafic (more-dense) oceanic crust (2). In particular, we determine the pressure–temperature (P-T) conditions of formation of the tonalite–trondhjemite–granodiorite (TTG) suite of granitoids—the principal crustal component of the Singhbhum Craton. The P-T data provide a time-integrated estimate of crustal thicknesses and elucidate the tectonic process controlling the craton’s emersion. These crustal thickness values are cross checked against the independent thickness estimates provided by the La-Yb systematics of the TTGs. Finally, a link between crustal thickening, maturation, and emersion is demonstrated via isostatic modeling.Open in a separate windowFig. 1.Spatial distribution and detrital zircon U-Pb ages of the Singhbhum cover sequence. (A) Simplified geological map of the Singhbhum Craton (29, 31) showing the outliers of the Singhbhum cover sequence and their granite–greenstone basement (SI Appendix, SI Text). The orange area in the Inset shows the location of the Singhbhum Craton within the Indian Peninsula. The younger (∼3.0 to 2.8 Ga) granitoids (including those of the Rengali Province) that intruded the outliers of the cover sequence are also shown. The formations comprising the outliers include: Mahagiri (Mhg), Pallahara-Mankaharchua (PM), Simlipal (Smp), Keonjhar (Kj), Birtola (Bir), Achu (Ac), Bisrampur (Brm), and Dhanjori (Dj). (B) Kernel density estimate (KDE) of <±10% discordant detrital zircon (²⁰⁷Pb/²⁰⁶Pb) ages from different outliers of the cover sequence (SI Appendix, Fig. S1). For each outlier, the white arrow shows the weighted mean ²⁰⁷Pb/²⁰⁶Pb age of the youngest detrital zircon population, which represents its maximum depositional age (SI Appendix, Fig. S1). The minimum depositional age (dashed gray line) of ∼2.94 Ga is constrained from a metamorphic event that affected the outliers. The colored bands show the age brackets of the different phases of granitoid magmatism and greenstone belt formation. Data are in Dataset S1. Refer to SI Appendix, Methods and SI Text for details.