Simultaneous recording of ATP-sensitive K+ current and intracellular Ca2+ in anoxic rat ventricular myocytes. Effects of glibenclamide

We investigated the temporal relationship between the adenosine triphosphate-sensitive K current (K _ATP current), hypoxic shortening and Ca accumulation in cardiomyocytes exposed to anoxia or metabolic inhibition. Whole-cell, patch-clamp experiments were performed with nonstimulated isolated rat heart ventricular muscle cells loaded with the Ca-sensitive fluorescent dye 1-[2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy]-2-(2′-amino-5′-methylphenoxy) ethane-N,N,N′,N′-tetraacetic acid (fura-2) via the patch pipette. After approximately 8 min anoxia, the K _ATP current started to rise and reached a maximum of 21.3 ± 3.7 nA (n = 5, recorded at 0 mV clamp potential) within 1–3 min. At that time hypoxic contracture also occurred. Resting cytoplasmic free calcium (Ca_i) did not change significantly before hypoxic shortening. After hypoxic contracture, the K _ATP current decreased and Ca_i started to rise, reaching about 1 μmol/l. The presence of glibenclamide (10 μmol/l) in the bath reduced the anoxia-induced K _ATP current by more than 50%, but did not significantly influence the time dependence of current, hypoxic shortening and Ca_i, or the magnitude of Ca_i. Metabolic inhibition with 1.5 mmol/l CN resulted in K _ATP current increase and hypoxic shortening, occurring somewhat earlier than under anoxia, but all other parameters were comparable. In non-patch-clamped cells loaded with fura-2 AM ester and field-stimulated with 1 Hz, 1 μmol/l glibenclamide had no significant effect on the magnitude of the Ca_i increase caused by exposure of the cells to 1.5 mmol/l CN⁻. After CN⁻ wash-out in non-patch-clamped cells, Ca_i declined, oscillated and finally returned to control values. It can be concluded that glibenclamide inhibits anoxia-induced K _ATP currents only partially and has no significant effect on anoxia-induced rise in resting Ca_i. Received: 3 November 1995/Received after revision: 9 January 1996/Accepted: 16 January 1996     

Activation of big conductance Ca2+-activated K+ channels (BK) protects the heart against ischemia–reperfusion injury

Activation of the large-conductance Ca²⁺-activated K⁺ channel (BK) in the cardiac inner mitochondrial membrane has been suggested to protect the heart against ischemic injury. However, these findings are limited by the low selectivity profile and potency of the BK channel activator (NS1619) used. In the present study, we address the cardioprotective role of BK channels using a novel, potent, selective, and chemically unrelated BK channel activator, NS11021. Using electrophysiological recordings of heterologously expressed channels, NS11021 was found to activate BK α + β1 channel complexes, while producing no effect on cardiac K_ATP channels. The cardioprotective effects of NS11021-induced BK channel activation were studied in isolated, perfused rat hearts subjected to 35 min of global ischemia followed by 120 min of reperfusion. 3 μM NS11021 applied prior to ischemia or at the onset of reperfusion significantly reduced the infarct size [control: 44.6 ± 2.0%; NS11021: 11.4 ± 2.0%; NS11021 at reperfusion: 19.8 ± 3.3% (p < 0.001 for both treatments compared to control)] and promoted recovery of myocardial performance. Co-administration of the BK-channel inhibitor paxilline (3 μM) antagonized the protective effect. These findings suggest that tissue damage induced by ischemia and reperfusion can be reduced by activation of cardiac BK channels.     

KATP channel current increases in postinfarction remodeled cardiomyocytes

Adenosintriphosphate-sensitive potassium channels (K_ATP channels) are an important linkage between the metabolic state of a cell and electrophysiological membrane properties. In this study, K_ATP channels were studied in myocytes of normal and remodeled myocardium of the rat. Myocardial infarction was induced by ligature of the left anterior descending artery. Remodeled myocytes were obtained from the hypertrophied posterior left ventricular wall and interventricular septum 3 months after infarction. The current through K_ATP channels was measured in whole-cell and inside-out patches by using the patch-clamp technique. After myocardial infarction, the heart weight/body weight ratio was doubled and the myocytes were hypertrophied yielding a cell capacitance of 266±16 pF compared to 122±12 pF in control cells. The amount of Kir6.2 protein was indistinguishable in corresponding regions of control and remodeled hearts. The ATP sensitivity of K_ATP channels in remodeled cells was significantly lower than in control cells (half maximum block at 115 μmol/l ATP in remodeled and at 71 μmol/l ATP in control cells). The maximum I _KATP density induced by metabolic inhibition was higher in small remodeled (176±15 pA/pF) than in control cells (127±11 pA/pF), but was unchanged in large remodeled cells. Both, the higher I _KATP density and the lower sensitivity of the K_ATP channels to ATP suggest that remodeled cardiomyocytes develop an improved tolerance to ischemia by stabilizing the resting potential and decreasing excitability.     

Hyperbaric oxygenation alleviates MCAO-induced brain injury and reduces hydroxyl radical formation and glutamate release

The present study examined the effect of hyperbaric oxygen (HBO) on the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA), the products of salicylate trapping of hydroxyl free radicals, and glutamate release in the striatum during acute ischemia and reperfusion. Non-HBO rats (n = 8) were subjected to 1-h ischemia. Study rats (n = 8) were treated with HBO at 2.8 ATA for 1 h during ischemia. Artificial CSF solution containing 5 mM sodium salicylate was perfused at 1 μl/min. Samples were continuously collected at 15 min intervals and the levels of 2,3-DHBA, 2,5-DHBA, and glutamate were analyzed. The lesion volume was determined by TTC stain. Occlusion of the middle cerebral artery induced a significant increase in the levels of 2,3-DHBA and 2,5-DHBA. A peak of approximately two and fourfold of baseline levels was reached at 45 min and was maintained at elevated levels during reperfusion. The level of glutamate increased approximately two times at 30 min during ischemia, continued to increase, and reached approximately three times baseline level during reperfusion. HBO significantly alleviated brain injury associated with decreased levels of 2,3-DHBA, 2,5-DHBA and glutamate. This study suggests that the decreased glutamate release and the reduced formation of hydroxyl free radicals might contribute to the neuroprotective effect of HBO.     

Inotropic and chronotropic effects of ischemic postconditioning on the model of isolated heart

The effects of global ischemia (45 min) and reperfusion (30 min) on left-ventricular developed pressure (LVDP), HR, and end-diastolic pressure were studied on isolated perfused rat heart. The following postconditioning protocols were used: 1) 3 cycles of reperfusion (10 sec) and ischemia (10 sec), total cycle duration 20 sec; 2) 6 cycles reperfusion of reperfusion (10 sec) and ischemia (10 sec), total cycle duration 20 sec; 3) 3 cycles of reperfusion (20 sec) and ischemia (20 sec), total cycle duration 40 sec; 4) 6 cycles of reperfusion (20 sec) and ischemia (20 sec), total cycle duration 40 sec; 5) 3 cycles of reperfusion (30 sec) and ischemia (30 sec), total cycle duration 60 sec. The use of several cycles of a total duration of 20 sec had no effect on LVDP, but reduced EDP throughout the reperfusion period. Postconditioning protocol consisting of three 40-sec cycles promoted LVDP recovery during the reperfusion, but had no effect on EDP and decelerated HP normalization. Six 40-sec cycles had no effect on LVDP and EDP, but impeded HR recovery during the reperfusion period. Postconditioning protocol consisting of three 60-sec cycles promoted LVDP increase during the reperfusion and reduced contracture, but these transient effects were accompanied by decelerated HP normalization.     

Treadmill pre-training suppresses the release of glutamate resulting from cerebral ischemia in rats

This study was designed to investigate the neuroprotective effect of treadmill pre-training against the over-release of glutamate resulting from cerebral ischemia. Sprague–Dawley rats underwent 2 weeks of treadmill run-training before cerebral ischemia was performed by middle cerebral artery occlusion. The level of glutamate in brain extracellular fluid was detected before, during and after ischemia/reperfusion. The expression of metabotropic glutamate receptor-1 (mGluR1) mRNA in striatum was examined after ischemia for 80 min and reperfusion for 240 min. Neurological defect score and brain infarction volumes were measured. The treadmill pre-training significantly suppressed the release of glutamate, and reduced the expression of mGluR1 mRNA at 59% (P < 0.01) and 62% (P < 0.05), respectively, as compared with the ischemia group. The neurological defect score and infarction volume were significantly improved by 75% (P < 0.01) and 74% (P < 0.01), respectively, in the pre-training group, as compared to the ischemia group. Treadmill pre-training has a significant neuroprotective function against ischemia/reperfusion injury, by suppressing glutamate release resulting from cerebral ischemia, and this effect may be mediated by downregulation of mGluR1.     

The exercise dose affects oxidative stress and brachial artery flow-mediated dilation in trained men

The aim of this investigation was to establish whether changes in oxidative stress and endothelial function following acute aerobic exercise are dose-dependent. Ten healthy trained men completed four exercise sessions: 50% VO_2peak for 30 min (moderate intensity moderate duration, MIMD), 50% VO_2peak for 60 min (moderate intensity long duration, MILD), 80% VO_2peak for 30 min (high intensity moderate duration, HIMD), and 80% VO_2peak for the time to reach the caloric equivalent of MIMD (high intensity short duration, HISD). Thiobarbituric acid reactive substances (TBARS) were measured as an index of oxidative stress and brachial artery flow-mediated dilation (FMD) was assessed as an index of endothelial function. Variables were measured at baseline, immediately post-exercise, 1 and 2 h post-exercise. Both HIMD (14.2 ± 2.5 μmol/L) and HISD (14.7 ± 1.9 μmol/L) TBARS differed from MIMD (11.8 ± 1.5 μmol/L) immediately post-exercise. TBARS increased from pre to immediately post-exercise for HIMD (12.6 ± 2.1 vs.14.2 ± 2.5 μmol/L) and HISD (12.3 ± 2.8 vs. 14.7 ± 1.9 μmol/L). Both MIMD (7.2 ± 2.2%) and HISD (7.6 ± 2.7%) FMD immediately post-exercise were greater than HIMD (4.7 ± 2.2%). An increase of FMD from pre to immediately post-exercise was found for MIMD (5.0 ± 2.5 vs. 7.2 ± 2.2%) and HISD (5.9 ± 2.4 vs. 7.6 ± 2.7%). These data suggest that acute exercise-induced TBARS are exercise intensity-dependent whereas FMD appears to improve following energy expenditure equivalent to 30 min 50% VO_2peak, regardless of intensity or duration.     

Cyclooxygenase-2 mediates the delayed cardioprotection induced by hydrogen sulfide preconditioning in isolated rat cardiomyocytes

We previously reported that hydrogen sulfide (H₂S) preconditioning (SP) produces cardioprotection in isolated rat cardiomyocytes. The present study was designed to determine the involvement of cyclooxygenase-2 (COX-2) in the SP-induced delayed cardioprotection. Isolated cardiac myocytes were treated with NaHS (100 μM, a H₂S donor) for 30 min and then cultured for 20 h followed by ischemia/reperfusion insults. SP significantly increased cell viability, percentage of rod-shaped cells, and myocyte contractility after 10 min of reperfusion. Given 30 min before and during lethal ischemia, two selective COX-2 inhibitors, NS-398 and celebrex, abrogated SP-induced cardioprotective effects. Moreover, SP upregulated the expression of COX-2 and increased PGE₂ production in the cardiac myocytes. These effects were significantly attenuated by glibenclamide, an ATP-sensitive K⁺ channel (K_ATP) blocker, and chelerythrine, a selective protein kinase C (PKC) inhibitor, suggesting that activation of both K_ATP and PKC is required for the stimulation of COX-2. Additionally, NG-nitro-l-arginine methyl ester, a nitric oxide synthase inhibitor, failed to regulate COX-2 protein expression but inhibited SP-enhanced COX-2 activity and PGE₂ production. In conclusion, we provided the first evidence that SP may produce delayed cardioprotection via K_ATP/PKC dependent induction of COX-2 expression and via nitric oxide-induced COX-2 activation.     

11,12-EET和缺血预处置对在体大鼠正常及再灌注心肌磷酸化ERK和p38MAPK表达的影响

目的:观察11,12-环氧二十碳三烯酸(11,12-EET)和缺血预处置对大鼠再灌注心肌组织磷酸化ERK1/ERK2和p38 MAPK表达的影响,了解大鼠心肌磷酸化ERK1/ERK2和p38 MAPK表达与预处置有否关系。方法: 使用雄性Wistar大鼠,通过结扎(60 min)和松开(30 min)冠状动脉左前降支,复制缺血/再灌注模型;采用缺血5 min,再灌注5 min两次造成缺血预处置。大鼠经手术并静脉给予6.24×10^-8mol/L 11,12-EET,稳定20 min,结扎冠脉复制缺血/再灌注模型。实验分5组:①正常组(norm);②假手术组(sham);③缺血再灌注组(I/R);④短阵缺血预处置组(SI+I/R);⑤11,12-EET预处置缺血/再灌注组(EET+I/R)。采用Western blot法测定心肌细胞外调节的蛋白激酶(ERK1/2)和p38 MAPK的表达程度,并观察再灌注过程中心功能的变化。结果: 再灌注30 min时,I/R组+dp/dt_max%、-dp/dt_max%和LVDP均显著低于sham组、SI+I/R组和EET+I/R组(P＜0.05);而I/R组大鼠心肌ERK1/2磷酸化表达明显高于sham组(P＜0.05),明显低于SI+I/R组和EET+I/R组(P＜0.05);I/R组大鼠心肌p38 MAPK磷酸化表达I/R组显著高于sham组、norm组、SI+I/R及EET+I/R组(P＜0.05)。结论:6.24×10^-8 11,12-EET mol/L具有保护心功能的作用,这种保护作用可能与大量激活磷酸化ERK1/2和抑制p38 MAPK有关。     

Effects of glucose,forskolin and tolbutamide on membrane potential and insulin secretion in the insulin-secreting cell line INS-1

Membrane voltages (V _m) of INS-1 cells, an insulin-secreting cell line, were measured mostly using the cell-attached mode of the patch-clamp method. The cell-attached configuration allowed the cell to be kept intact. Measurement of V _m was possible because seal resistances were very high and because the membrane obviously had a sufficiently high conductance (probably via K⁺ channels). Resting V _m was −80 ± 1mV (n = 42) and was mainly determined by sulphonylurea-sensitive K⁺ _ATP channels since tolbutamide depolarized the plasma membrane in a concentration-dependent manner and generated action potentials at 50 and 100 μmol/l. D-Glucose, tested between 0.5 and 16.7 mmol/l, also depolarized the plasma membrane in a concentration-dependent manner and induced action potentials at concentrations higher than 5.6 mmol/l. Similarly, forskolin (5 μmol/l) depolarized the cells and increased the frequency of Ca²⁺-mediated action potentials. Insulin secretion was measured from cells growing in culture dishes, by radioimmunoassay. Glucose doubled secretion in INS-1 cells, whereas tolbutamide had no significant effect on secretion in the presence of 0.5 mmol/l and 16.7 mmol/l glucose. At 3 mmol/l glucose, tolbutamide increased insulin release slightly. Forskolin elevated secretion twofold at a low glucose concentration. In contrast, when glucose or tolbutamide were added together with forskolin secretion was potentiated five- to tenfold. These results show that glucose induces membrane activation in INS-1 cells. Furthermore, the potent effect of tolbutamide, i.e. to depolarize the plasma membrane without inducing insulin release, leads to the conclusion that effects distal to depolarization are pivotal for secretion in INS-1 cells. Received: 21 November 1995/Accepted: 18 April 1996     

Hemodilution with liposome-encapsulated low-oxygen-affinity hemoglobin does not attenuate hypothermic cerebral ischemia in rats

Hypothermia decreases cerebral metabolism and increases hemoglobin oxygen affinity. A hypothesis that the reversal of increased oxygen affinity would further attenuate hypothermic cerebral ischemia was tested by evaluating the effects of liposome-encapsulated hemoglobin (LipoHb) with low oxygen affinity (P₅₀ = 40–50 mmHg) on hypothermic incomplete cerebral ischemia. Wistar rats were randomly assigned to one of the following two groups: (A) exchange transfusion with LipoHb solution (Hb = 6 g/dl) (LipoHb, n = 5), (B) no exchange transfusion (control, n = 5). After surface cooling to 22°C, forebrain ischemia was induced for 15 min by bilateral carotid artery occlusion combined with a decrease in the mean arterial pressure (MAP) to 40 mmHg. ³¹P-magnetic resonance spectroscopy was performed during ischemia and 45 min of reperfusion. After reperfusion, MAP was significantly higher in the control group than in the LipoHb group (P < 0.01), although there were no significant differences during ischemia. Intracellular pH and phosphocreatine (PCr) levels decreased during ischemia and returned to the preischemic level in both groups following reperfusion. The LipoHb group had a significantly larger decrease and smaller recovery in PCr than the control group (P < 0.0001). Althouth β-adenosine triphosphate decreased during ischemia in the LipoHb group, it increased in the control group (P < 0.0001). Inorganic phosphate (Pi) increased during ischemia and decreased to the normal value after reperfusion. The LipoHb group experienced a significantly larger production of Pi than the control group (P = 0.02). Hemodilution with high-P₅₀ LipoHb does not reduce ischemic energy depletion induced by hypothermic incomplete forebrain ischemia in rats.     

Cl– secretion induced by 5-hydroxytryptamine and calcitonin gene-related peptide in rat tracheal epithelia

 The effects of 5-hydroxytryptamine (5-HT) and calcitonin gene-related peptide (CGRP), which are colocalized in nerve terminals in the airway, on Cl^– secretion in rat tracheal epithelia were tested. Short-circuit current (I _sc) was measured after rat tracheal epithelial monolayers were cultured on porous filters. In rat tracheal monolayers 5-HT and CGRP increased I _sc upon addition to the serosal compartment, in a dose-dependent manner with EC₅₀ values at 5 μmol/l and 5 nmol/l, respectively. The responses were dependent on the presence of Cl^– in the bathing solution and were inhibited by 100 μmol/l bumetanide. When 5-HT or CGRP was added after the administration of forskolin, the responses were not observed. 5-HT and CGRP increased the intracellular cAMP concentration. Low-Ca²⁺ buffer (0.1 mmol/l) and pretreatment with BAPTA/AM (10 μmol/l), thapsigargin (1 μmol/l) or indomethacin (10 μmol/l) did not affect the responses to 5-HT and CGRP. The 5-HT-induced response was not inhibited by 5-HT₂ and/or 5-HT₄ antagonists. These results indicate that in the rat tracheal epithelia 5-HT and CGRP increase Cl^– secretion by an increase in intracellular cAMP concentration via direct activation of basolateral receptors, and that the response to 5-HT is not mediated via 5-HT₄ receptors. Received: 8 January 1997 / Received after revision: 11 June 1997 / Accepted: 23 July 1997     

<Emphasis Type="Italic">In Vivo</Emphasis> Reduction of Reperfusion Injury to the Heart with Apelin-12 Peptide in Rats

Apelin-12 (A-12) peptide was synthesized by automated solid phase method and purified by reverse phase HPLC. Its homogeneity and structure were confirmed by HPLC, ¹H-NMR spectroscopy, and mass spectroscopy. Acute myocardial infarction was induced by 40-min occlusion of the left coronary artery with subsequent 60-min reperfusion in narcotized Wistar rats. Peptide A-12 was injected (intravenous bolus, 0.07 or 0.35 μmol/kg) to experimental animals simultaneously with the beginning of reperfusion. Injections of A-12 in these doses led to reduction of systolic BP to 67 and 85% of the initial level, respectively, which was virtually restored completely by the end of reperfusion, and to a significant reduction of the infarction focus in the myocardium (by 21 and 34% in comparison with the control, respectively). Injection of A-12 in a dose of 0.35 μmol/kg led to reduction of plasma concentrations of necrosis markers in comparison with the control by the end of reperfusion: MB-creatine kinase by 56%, lactate dehydrogenase by 30%. The results attest to vasodilatory effects of A-12 under conditions of heart reperfusion in vivo; the peptide injected after local ischemia limits the myocardial infarction size and reduces damage to cardiomyocyte membrane.     

Cardiodepressant mediators are released after myocardial ischaemia: modulation by catecholamines and adenosine

The interaction of recently characterized cardiodepressant mediators with catecholamines and adenosine after myocardial ischaemia was investigated using a model of sequential perfusion of two isolated guinea-pig hearts. Sequential perfusion was initiated after 10, 20, and 30 min (group I, II, and III) of global ischaemia in the first heart. At the onset of sequential perfusion LVdP/dt_max and _min of Heart II decreased by 46 and 44% in group I, by 28 and 34% in group II, and increased by 60 and 24% in group III. Infusion of the β₁-receptor antagonist metoprolol (2.8 μmol L^–1) into Heart II did not modulate contractile changes after 10 min of ischaemia in Heart I, prevented the attenuation of the cardiodepressant effect after 20 min of ischaemia, and completely reversed the positive inotropic effect after 30 min of ischaemia. The A1- and A2-receptor antagonists DPCPX (2 μmol L^–1) and DMPX (20 μmol L^–1) enhanced the positive inotropic and lusitropic effects in Heart II (LVdP/dt_max +154%, LVdP/dt_min +71%) during sequential perfusion after 30 min of ischaemia in Heart I. It is concluded that the effects of cardiodepressant mediators released after myocardial ischaemia are counteracted by a time-dependent release of catecholamines. Endogenous cardiac adenosine, in turn, attenuates the modulatory effects of catecholamines.     

缺血后处理对离体大鼠心肌线粒体功能的影响

目的：建立离体大鼠心肌缺血/再灌注损伤模型,观察缺血后处理对大鼠心肌线粒体功能的影响,并探讨线粒体ATP敏感性钾通道（mitoK_ATP）在缺血后处理心肌保护中的作用。方法：采用Langendorff装置建立离体大鼠心肌缺血/再灌注损伤模型。将SD大鼠随机分为对照组（C）、模型组（M）、缺血后处理组（IPO）、5-羟癸酸拮抗缺血后处理组（5-HD+IPO）,每组8只。各组均先灌注平衡20 min,C组：续灌70 min;M组：缺血前灌注4 ℃ St.Thomas停跳液（10 mL/kg）,全心缺血40 min,复灌30 min;IPO组：全心缺血40 min,复灌前先开放10 s,缺血10 s,反复6次,时间为2 min,复灌28 min;5-HD+IPO组：缺血后处理前给予含5-羟癸酸（100 μmol/L）的K-H液灌注5 min,余同IPO组,复灌23 min。观察各组平衡末与再灌注末心肌线粒体膜电位、氧自由基及呼吸功能的变化。结果：(1) 各组再灌注末心肌线粒体膜电位较平衡末显著降低,而C组显著高于其它3组,IPO组明显高于5-HD+IPO与M组,5-HD +IPO组高于M组。(2) 各组再灌注末与平衡末比较,心肌线粒体氧自由基含量显著升高,其中M组显著高于其它3组,5-HD +IPO组高于IPO及C组,IPO组高于C组。(3) 各组再灌注末较平衡末线粒体呼吸功能明显受损,且C组优于其它3组,IPO组优于5-HD+IPO与M组,5-HD +IPO组优于M组。结论：(1) 缺血后处理通过维护线粒体膜电位稳定、减少线粒体氧自由基的产生、保护线粒体呼吸链及功能,减轻心肌的再灌注损伤。(2) 5-HD不能完全阻断缺血后处理的心肌保护作用。(3) 缺血后处理的心肌保护效应可通过激活心肌mitoK_ATP实现,同时还有其它因素参与了缺血后处理的心肌保护。     

Effect of regular exercise on homocysteine concentrations: the HERITAGE Family Study

We investigated whether regular aerobic exercise could affect plasma total homocysteine (tHcy), and whether there were sex-related or racial differences in tHcy changes. Data were available for 816 black and white men and women, aged 17–65 years, 711 of whom completed a 20 week aerobic exercise training program. The tHcy concentration was measured in frozen plasma samples by an HPLC method. In Blacks, tHcy did not change with exercise training [men −0.5 (SD 3.7) μmol/l, women 0.0 (2.2) μmol/l) but increased significantly in Whites (men +0.3 (1.7) μmol/l, women +0.2 (1.6) μmol/l). No sex-related differences were found in either racial group. Changes in tHcy correlated negatively with baseline homocysteine (r = −0.40, P < 0.0001). Homocysteine levels of the “High” (hyperhomocysteinemia) (≥15 μmol/l) group (n = 30) decreased significantly with regular aerobic exercise from 23.1 (12.1) to 19.6 (7.6) μmol/l. Homocysteine levels of the “Normal” group increased slightly from 8.2 ± 2.2 to 8.5 ± 2.4 μmol/l. Men exhibit racial differences for tHcy responses to exercise training. Regular aerobic exercise has favorable effects on individuals with hyperhomocysteinemia, but tHcy slightly increased in individuals within the normal range.     

The relationship between mitochondrial respiration and postischemic recovery of isolated heart contractility

Recovery of heart contractility after global normothermic ischemia in New-Zealand rabbits depends on the reperfusion mode and the composition of reperfusion medium and correlates with mitochondrial respiration. Cardiac function can recover also at low ATP concentration (about 1 μmol/g dry tissue). Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 126, No. 11, pp. 538–541, November, 1998     

Supplemental oxygen and muscle metabolism in mitochondrial myopathy patients

Patients with mitochondrial myopathy (MM) have a reduced capacity to perform exercise due to a reduced oxidative capacity. We undertook this study to determine whether skeletal muscle metabolism could be improved with oxygen therapy in patients with MM. Six patients with MM and six controls, matched for age, gender and physical activity, underwent ³¹P-magnetic resonance spectroscopy (³¹P-MRS) examination. ³¹P-MR spectra were collected at rest and in series during exercise and recovery whilst breathing normoxic (0.21 O₂) or hyperoxic (1.0 O₂) air. At rest, MM showed an elevated [ADP] (18 ± 3 μmol/l) and pH (7.03 ± 0.01) in comparison to the control group (12 ± 1 μmol/l, 7.01 ± 0.01) (P < 0.05) consistent with mitochondrial dysfunction. Oxygen supplementation did not change resting metabolites in either MM or the control group (P > 0.05). Inferred maximal ATP synthesis rate improved by 33% with oxygen in MM (21 ± 3 vs. 28 ± 5 mmol/(l min), P < 0.05) but only improved by 5% in controls (40 ± 3 vs. 42 ± 3 mmol/(l min), P > 0.05). We conclude that oxygen therapy is associated with significant improvements in muscle metabolism in patients with MM. These data suggest that patients with MM could benefit from therapies which improve the provision of oxygen.     

Insight in Human Skin Microcirculation Using In Vivo Reflectance-Mode Confocal Laser Scanning Microscopy

Reflectance-mode confocal laser scanning microscopy allows in vivo imaging of the human skin. We hypothesized that this high-resolution technique enables observation of dynamic changes of the cutaneous microcirculation. Twenty-two volunteers were randomly divided in two groups. Group 1 was exposed to local heating and group 2 to local cold stress. Confocal microscopy was performed prior t ₀ (control), directly t ₁ and 5 min t ₂ after local temperature changes to evaluate quantitative blood cell flow, capillary loop diameter, and density of dermal capillaries. In group 1, blood flow increased at t ₁ (75.82 ± 2.86/min) and further at t ₂ (84.09 ± 3.39/min) compared to the control (61.09 ± 3.21/min). The control capillary size was 9.59 ± 0.25 μm, increased to 11.16 ± 0.21 μm (t ₁) and 11.57 ± 0.24 μm (t ₂). The dermal capillary density increased in t ₁ (7.26 ± 0.76/mm²) and t ₂ (8.16 ± 0.52/mm²), compared to the control (7.04 ± 0.62/mm²). In group 2, blood flow decreased at t ₁ (41.73 ± 2.61/min) and increased at t ₂ (83.27 ± 3.29/min) compared to the control (60.73 ± 2.90/min). The control capillary size was 9.55 ± 0.25 μm, decreased at t ₁ (7.78 ± 0.26 μm) and increased at t ₂ (11.38 ± 0.26 μm). Capillary density decreased at t ₁ (5.01 ± 0.49/mm²) and increased at t ₂ (7.28 ± 0.53/mm²) compared to the control (7.01 ± 0.52/mm²). Confocal microscopy is a sensitive and noninvasive imaging tool for characterizing and quantifying dynamic changes of cutaneous microcirculation on a histomorphological level.