Adenosine-mediated cardioprotection in ischemic-reperfused mouse heart.

We investigated the roles of A1, A2A, or A3 receptors and purine salvage in cardioprotection with exogenous adenosine, and tested whether A2A -mediated reductions in perfusion pressure modify post-ischemic recovery. Treatment with 10(-5) or 5 x 10(-5) M adenosine improved contractile recovery from 20 min ischemia 45 min reperfusion in isolated mouse hearts. Protection was attenuated by adenosine kinase inhibition (10(-5) M iodotubercidin) and receptor antagonism (5 x 10(-5) M 8-rho-sulfophenyltheophylline, 8-SPT). Enzyme efflux mirrored contractile recoveries. A 3 agonism with 10(-7) M 2-chloro- N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA) improved ischemic tolerance whereas A1 agonism with 5 x 10(-8) M N6-cyclopentyladenosine (CPA) and A2A agonism with 10(-9) M 2-[p-(2-carboxyethyl) phenethylamino]-5'-N-ethylcarboxamidoadenosine (CGS21680) or 2 x 10(-8) M methyl-4-(3-[9-[4S,5S,2R,3R)-5-(N-ethylcarbamoyl)-3,4-dihydroxyoxolan-2-yl]-6-aminopurin-2-yl)]prop-2-ynyl) cyclohexane-carboxylate (ATL-146e) were ineffective. Protection via A1 receptor overexpression was enhanced by adenosine, but unaltered by A1 or A2A agonists. Finally, post-ischemic dysfunction in hearts perfused at constant flow was dependent on coronary pressure, with A2A AR-mediated reductions in pressure reducing diastolic contracture, and elevated perfusion pressure worsening contracture. Data indicate that cardioprotection with exogenous adenosine in asanguinous hearts involves purine salvage and activation of A3 but not A1 or A2A receptors.     

Comparison of bisoprolol and carvedilol cardioprotection in a rabbit ischemia and reperfusion model

Carvedilol, a selective alpha(1) and non-selective beta-adrenoceptor antagonist and antioxidant, has been shown to provide significant cardiac protection in animal models of myocardial ischemia. To further explore the mechanisms contributing to the efficacy of carvedilol cardioprotection, the effects of carvedilol on hemodynamic variables, infarct size and myeloperoxidase activity (an index of neutrophil accumulation) were compared with a beta(1) selective adrenoceptor antagonist, bisoprolol. Carvedilol (1 mg/kg) or bisoprolol (1 mg/kg) was given intravenously 5 min before reperfusion. In vehicle-treated rabbits, ischemia (45 min) and reperfusion (240 min) resulted in significant increases in left ventricular end diastolic pressure, large myocardial infarction (64.7+/-2.6% of area-at-risk) and a marked increase in myeloperoxidase activity (64+/-14 U/g protein in area-at-risk). Carvedilol treatment resulted in sustained reduction of the pressure-rate-index and significantly smaller infarcts (30+/-2.9, P<0.01 vs. vehicle) as well as decreased myeloperoxidase activity (26+/-11 U/g protein in area-at-risk, P<0.01 vs. vehicle). Administration of bisoprolol at 1 mg/kg resulted in a pressure-rate-index comparable to that of carvedilol and also decreased infarct size (48.4+/-2.5%, P<0.001 vs. vehicle, P<0.05 vs. carvedilol), although to a significantly lesser extent than that observed with carvedilol. Treatment with bisoprolol failed to reduce myeloperoxidase activity in the ischemic myocardial tissue. In addition, carvedilol, but not bisoprolol, markedly decreased cardiac membrane lipid peroxidation measured by thiobarbituric acid formation. Taken together, this study suggests that the superior cardioprotection of carvedilol over bisoprolol is possibly the result of carvedilol's antioxidant and anti-neutrophil effects, not its hemodynamic properties.     

ATP敏感性钾通道和线粒体通透转换孔参与白藜芦醇苷的心肌保护作用(英文)

目的探讨白藜芦醇苷(Poly)对大鼠缺血再灌注(I-R)心肌损伤的保护作用及其机制。方法应用Langendorff室技术制备离体大鼠心脏I-R损伤模型。雄性SD大鼠随机分为对照组、模型组、Poly(25, 50和75μmol.L-1)组、格列本脲(Gli) +Poly组、5-羟基癸酸(5-HD) +Poly组和苍术苷(Atr) +Poly组。对照组心脏由K-H液灌流110 min;模型组由K-H液灌流20 min后,停灌30 min,复灌60min;Poly组在I-R处理前用含不同浓度Poly的K-H液灌流10 min;Gli +Poly和5-HD+Poly组在I-R前分别用含Gli (10μmol.L-1)和5-HD(100μmol.L-1)的K-H液灌流5 min,再加入Poly (50μmol.L-1)灌流10 min;Atr +Poly组用含Poly(50μmol.L-1)K-H液灌流10 min及停灌30 min后,先用含Atr(20μmol.L-1)的K-H液灌流15 min,然后改用K-H液灌流。分别记录各组停灌前、停灌30 min和复灌60 min内的左心室舒张末压(LVEDP)、左心室舒张压(LVDP)、左心室等容期压力最大变化速率(±dp/dtmax)和冠脉流量(CF)等心功能指标。心脏复灌60 min后,用氯化三苯基四氮唑染色法测定心肌梗死面积,透射电镜下检测心肌超微结构变化。结果缺血前各组心功能参数无明显变化。与模型组相比,Poly可浓度依赖性地促进大鼠I-R后心功能的恢复,预防I-R损伤。复灌60 min后,Poly组大鼠心脏LVDP,±dp/dtmax和CF明显高于模型组;LVEDP则低于模型组;缺血前给予Poly(50μmol.L-1)10 min可明显减小I-R后心肌梗死面积,并改善心肌超微结构。Gli, 5-HD和Atr可阻断Poly对I-R心脏心功能参数和心肌梗死面积等的保护作用。结论 Poly具有明显的抗心肌I-R损伤作用,其心脏保护作用可能与其增加细胞膜和线粒体膜ATP敏感性钾通道开放和抑制线粒体通透转换孔开放有关。     

A pharmacologic activator of endothelial KCa channels increases systemic conductance and reduces arterial pressure in an anesthetized pig model

SKA-31, an activator of endothelial KCa2.3 and KCa3.1 channels, reduces systemic blood pressure in mice and dogs, however, its effects in larger mammals are not well known. We therefore examined the hemodynamic effects of SKA-31, along with sodium nitroprusside (SNP), in anesthetized, juvenile male domestic pigs. Experimentally, continuous measurements of left ventricular (LV), aortic and inferior vena cava (IVC) pressures, along with flows in the ascending aorta, carotid artery, left anterior descending coronary artery and renal artery, were performed during acute administration of SKA-31 (0.1, 0.3, 1.0, 3.0 and 5.0 mg/ml/kg) and a single dose of SNP (5.0 μg/ml/kg). SKA-31 dose-dependently reduced mean aortic pressure (mP_AO), with the highest dose decreasing mP_AO to a similar extent as SNP (− 23 ± 3 and − 28 ± 4 mm Hg, respectively). IVC pressure did not change. Systemic conductance and conductance in coronary and carotid arteries increased in response to SKA-31 and SNP, but renal artery conductance was unaffected. There was no change in either LV stroke volume (SV) or heart rate (versus the preceding control) for any infusion. With no change in SV, drug-evoked decreases in LV stroke work (SW) were attributed to reductions in mP_AO (SW vs. mP_AO, r² = 0.82, P < 0.001). In summary, SKA-31 dose-dependently reduced mP_AO by increasing systemic and arterial conductances. Primary reductions in mP_AO by SKA-31 largely account for associated decreases in SW, implying that SKA-31 does not directly impair cardiac contractility.     

Fenofibrate attenuates impaired ischemic preconditioning-mediated cardioprotection in the fructose-fed hypertriglyceridemic rat heart

We investigated in this study whether or not the ischemic preconditioning (IPC)-mediated cardioprotective effect against ischemia–reperfusion (I/R) injury exists in the fructose-fed hypertriglyceridemic (HTG) rat heart. Langendorff-perfused normal and fructose-fed (10 %?w/v in drinking water, 8 weeks) HTG rat hearts were subjected to 30-min global ischemia and 120-min reperfusion. IPC protocol included four brief episodes (5 min each) of ischemia and reperfusion. Myocardial infarct size using triphenyltetrazolium chloride staining, markers of cardiac injury such as lactate dehydrogenase (LDH) and creatine kinase (CK-MB) release, coronary flow rate (CFR), and myocardial oxidative stress were assessed. High degree of myocardial I/R injury, by means of significant myocardial infarct size, elevated coronary LDH and CK-MB release, reduced CFR, and high oxidative stress, was noted in the HTG rat heart as compared to the normal rat heart. The IPC-mediated cardioprotection against I/R injury was markedly impaired in the HTG rat heart as compared to the normal rat heart. Interestingly, pharmacological reduction of triglycerides using 8-week treatment protocol with fenofibrate (80 mg/kg/day, p.o.) restored the IPC effect in the HTG rat heart that was blunted by coinfusion, during the IPC reperfusion protocol, of a specific inhibitor of phosphoinositide-3-kinase (PI3-K), wortmannin (100 nM). The IPC failed to protect the HTG rat heart against I/R injury. Fenofibrate treatment reduced high triglycerides in the fructose-fed HTG rat and subsequently restored the cardioprotective effect of IPC.     

Mechanisms by which K(ATP) channel openers produce acute and delayed cardioprotection

Mitochondria are being increasingly studied for their critical role in cell survival. Multiple diverse signaling pathways have been shown to converge on the K+-sensitive ATP channels as the effectors of cytoprotection against necrosis and apoptosis. The role of potassium channel openers in regulation and transformation of cell membrane excitability, action potential and electrolyte transfer has been extensively studied. Cardiac mitoK(ATP) channels are the key effectors in cardioprotection during ischemic preconditioning, as yet with an undefined mechanism. They have been hypothesized to couple myocardial metabolism with membrane electrical activity and provide an excellent target for drug therapy. A number of K(ATP) channel openers have been characterized for their beneficial effects on the myocardium against ischemic injury. This review updates recent progress in understanding the physiological role of K(ATP) channels in cardiac protection induced by preconditioning and highlights relevant questions and controversies in the light of published data.     

Effects of the novel calcium channel blocker,anipamil, on the isolated rabbit heart

Summary The calcium channel blocking activity of the novel phenylalkylamine derivative, anipamil, was tested on the isolated rabbit heart, in comparison with verapamil and gallopamil. Anipamil and the other calcium channel blockers lower left ventricular pressure in the same concentration range (10^–8 –10^–4 mol/1). The negative inotropic effect of anipamil is only partially reversed (nearly 65%) by rising calcium concentration in the perfusion fluid, whilst a complete recovery is observed for verapamil and gallopamil. The negative inotropic effect of anipamil is of rapid onset but long lasting, being still present 12 h after washout. On the contrary, that of gallopamil or verapamil completely disappears within 3 h of washout.Verapamil and gallopamil (10^–8 –10^–4 mol/1) depress spontaneous heart rate up to asystolia and abolish the vasopressin- and Bay K 8644-induced coronary spasm. Anipamil, on the contrary, does not modify coronary spasm elicited by both stimulants and spontaneous heart rate up to 10^–4 mol/l.These observations suggest that anipamil, in the isolated rabbit heart, possesses a peculiar pharmacological profile, since its calcium channel blocking activity is confined to the myocardial muscle.     

Effects of propofol on GABAA channel conductance in rat-cultured hippocampal neurons

Channels were activated, in ripped-off patches from rat-cultured hippocampal neurons, by propofol alone, propofol plus 0.5 μM GABA (γ-aminobutyric acid) or GABA alone. The propofol-activated currents were chloride-selective, showed outward-rectification and were enhanced by 1 μM diazepam. The maximum propofol-activated channel conductance increased with propofol concentration from less than 15 pS (10 μM) to about 60 pS (500 μM) but decreased to 40 pS in 1 mM propofol. Fitting the data from 10 to 500 μM propofol with a Hill-type equation gave a maximum conductance of 64 pS, an EC₅₀ value of 32 μM and a Hill coefficient of 1.1. Addition of 0.5 μM GABA shifted the propofol EC₅₀ value to 10 μM and increased the maximum channel conductance to about 100 pS. The Hill coefficient was 0.8. The maximum channel conductance did not increase further when 1 μM diazepam was added together with a saturating propofol concentration and GABA. The results are compared to effects other drugs have on GABA_A channels conductance.     

Nitric oxide fails to confer endogenous antiarrhythmic cardioprotection in the primate heart in vitro

BACKGROUND AND PURPOSE: The role of nitric oxide (NO) in cardiac pathophysiology remains controversial. According to data from several studies using rat and rabbit isolated hearts, NO is an endogenous cardioprotectant against reperfusion-induced ventricular fibrillation (VF). Thus, if cardiac NO production is abolished by perfusion with L-N(G)-nitro-L-arginine methylester (L-NAME) (100 microM) there is a concomittant increase in the incidence of reperfusion-induced VF, with L-NAME's effects on NO and VF prevented by L- (but not D-) arginine co-perfusion. To make a better estimate of the clinical relevance of these findings, 100 microM L-NAME was tested in primate hearts under similar conditions. EXPERIMENTAL APPROACH: Marmoset (Callithrix jaccus) hearts, isolated and perfused, were subjected to 60 min left regional ischaemia followed by 10 min reperfusion in vitro. The ECG was recorded and NO in coronary effluent measured by chemiluminescence. KEY RESULTS: L-NAME (100 micro M) decreased NO in coronary effluent throughout ischaemia and reperfusion (e.g. from 3720+/-777 pmol min(-1) g(-1) in controls to 699+/-98 pmol min(-1) g(-1) after 5 min of ischaemia) and, during ischaemia, lowered coronary flow and reduced heart rate, actions identical to those seen in rat and rabbit hearts. However, the incidence of reperfusion-induced VF was unchanged (20%, with or without L-NAME). CONCLUSIONS AND IMPLICATIONS: A species difference exists in the effectiveness of endogenous NO to protect hearts against reperfusion-induced VF. The present primate data, which presumably take precedence over rat and rabbit data, cast doubt on the clinical relevance of NO as an endogenous, antiarrhythmic, cardioprotectant.     

Mitochondrial toxicity of 2-bromohydroquinone in rabbit renal proximal tubules

2-Bromohydroquinone (BHQ) is a nephrotoxic metabolite of bromobenzene and a model toxic hydroquinone. The primary goal of these studies was to determine whether BHQ produces toxicity in rabbit renal proximal tubules by inhibiting mitochondrial function. BHQ induces a specific sequence of cellular events. Initially there was decrease in tubular glutathione content followed by a decrease in nystatin-stimulated ouabain-sensitive respiration. A decrease in cell viability, as measured by a decrease in lactate dehydrogenase retention, was late event. Associated with the decrease in respiration was a decrease in intracellular ATP content. Probing of mitochondrial function in the tubule revealed that BHQ did inhibit mitochondrial function in a somewhat selective manner. State 3 respiration was inhibited prior to changes in the rate of electron flow through cytochrome c-cytochrome oxidase. It is postulated that BHQ may initially inhibit state 3 respiration by inhibiting the adenine nucleotide translocator and/or the F1-ATPase.     

Mitochondrial function in ischaemia and reperfusion of the ageing heart

1. In addition to Ca2+-dependent mediation of excitation-contraction coupling during cardiac work and ATP hydrolysis, Ca2+ also stimulates the Krebs' cycle and mitochondrial matrix dehydrogenases to maintain the nicotinamide adenine dinucleotide redox potential and ATP synthesis. Thus, the balance between energy demand and supply is maintained during increases in cardiac work by elevated cytosolic Ca2+ that is transmitted to the mitochondrial matrix via regulation of uniporter and antiporter pathways across the inner mitochondrial membrane. 2. Brief ischaemia perturbs Ca2+ homeostasis but mitochondrial buffering of Ca2+ permits maintained mitochondrial function. However, prolonged ischaemia and reperfusion causes Ca2+ 'overload' at supramicromolar levels. The onset of vicious cycles that abrogate contractile function and, ultimately, may cause irreversible cell injury involves: (i) loss of ionic homeostasis, energy production and anti-oxidant enzyme activity; (ii) activation of phospholipases; and (iii) accumulation of free radicals, membrane lipid peroxidation products and protein adducts. 3. Increased permeability of the inner mitochondrial membrane to solutes occurs causing mitochondrial swelling, 'proton leak', reduced efficiency of the respiratory chain and uncoupling of oxidative phosphorylation. The opening of the mitochondrial permeability transition pore is potentiated by high mitochondrial Ca2+ and inducers, such as Pi, long-chain acyl coenzyme (Co)A and oxygen free radicals. Opening of this channel depolarizes the mitochondrion and dissipates the H+ electrochemical gradient (delta muH), preventing oxidative phosphorylation. Together with the release of cytochrome c and subsequent activation of caspase pathways, these events precede cell death. 4. Compared with younger counterparts, the senescent myocardium has a reduced capacity to recover from ischaemia and reperfusion. The consequent events described above are augmented in ageing. Elevated mitochondrial Ca2+ and increased dehydrogenase activation are linked to inefficient mitochondrial function and limited postischaemic recovery of contractile function. 5. Notably, a distinct decrease in the ratio of mitochondrial membrane omega-3 to omega-6 polyunsaturated fatty acids (PUFA) and a decrease in the mitochondrial phospholipid cardiolipin occurs in aged rat hearts. A diet rich in omega-3 PUFA directly increases membrane omega-3:omega-6 PUFA and cardiolipin content and also facilitates improved tolerance of ischaemia and reperfusion. A major consequence of dietary omega-3 PUFA may be the effect of altered mitochondrial Ca2+ flux and Ca2+-dependent processes.     

二乙酰单肟抑制豚鼠和鸡胚心肌细胞离子通道电导

二乙酰单肟抑制豚鼠和鸡胚心肌细胞离子通道电导佐田英明，伴隆志（日本国山口县宇部市山口大学医学部药理学讲座）ＮｉｃｈｏｌａｓＳＰＥＲＥＬＡＫＩＳ（ＤｅｐａｒｔｍｅｎｔｏｆＭｏｌｅｃｕｌａｒａｎｄＣｅｌｕｌａｒＰｈｙｓｉｏｌｏｇｙ，ＣｏｌｅｇｅｏｆＭｅｄ...     

Cyclic GMP-mediated inhibition of L-type Ca2+ channel activity by human natriuretic peptide in rabbit heart cells.

1. Effects of atrial natriuretic peptide (ANP) on the L-type Ca2+ channels were examined in rabbit isolated ventricular cells by use of whole-cell and cell-attached configurations of the patch clamp methods. ANP produced a concentration-dependent decrease (10-100 nM) in amplitude of a basal Ca2+ channel current. 2. The inactive ANP (methionine-oxidized ANP, 30 nM) failed to decrease the current. 3. 8-Bromo-cyclic GMP (300 microM), a potent activator of cyclic GMP-dependent protein kinase (PKG), produced the same effects on the basal Ca2+ channel current as those produced by ANP. The cyclic GMP-induced inhibition of the Ca2+ channel current was still evoked in the presence of 1-isobutyl-3-methyl-xanthine, an inhibitor of phosphodiesterase. ANP failed to produce inhibition of the Ca2+ channel current in the presence of 8-bromo-cyclic GMP. 4. In the single channel recording, ANP and 8-bromo-cyclic GMP also inhibited the activities of the L-type Ca2+ channels. Both agents decreased the open probability (NPo) without affecting the unit amplitude. 5. The present results suggest that ANP inhibits the cardiac L-type Ca2+ channel activity through the intracellular production of cyclic GMP and then activation of PKG.     

Mitochondrial fatty acid oxidation alterations in heart failure,ischaemic heart disease and diabetic cardiomyopathy

Heart disease is a leading cause of death worldwide. In many forms of heart disease, including heart failure, ischaemic heart disease and diabetic cardiomyopathies, changes in cardiac mitochondrial energy metabolism contribute to contractile dysfunction and to a decrease in cardiac efficiency. Specific metabolic changes include a relative increase in cardiac fatty acid oxidation rates and an uncoupling of glycolysis from glucose oxidation. In heart failure, overall mitochondrial oxidative metabolism can be impaired while, in ischaemic heart disease, energy production is impaired due to a limitation of oxygen supply. In both of these conditions, residual mitochondrial fatty acid oxidation dominates over mitochondrial glucose oxidation. In diabetes, the ratio of cardiac fatty acid oxidation to glucose oxidation also increases, although primarily due to an increase in fatty acid oxidation and an inhibition of glucose oxidation. Recent evidence suggests that therapeutically regulating cardiac energy metabolism by reducing fatty acid oxidation and/or increasing glucose oxidation can improve cardiac function of the ischaemic heart, the failing heart and in diabetic cardiomyopathies. In this article, we review the cardiac mitochondrial energy metabolic changes that occur in these forms of heart disease, what role alterations in mitochondrial fatty acid oxidation have in contributing to cardiac dysfunction and the potential for targeting fatty acid oxidation to treat these forms of heart disease.

LINKED ARTICLES

This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8     

Synthesis and characterisation of NS13558: a new important tool for addressing KCa1.1 channel function ex vivo

Pharmacological activation of the large-conductance Ca²⁺-activated K⁺ channel (KCa1.1) in the cardiac inner mitochondrial membrane has been found to protect the heart against ischemia reperfusion injuries. However, there are concerns about the selectivity of the pharmacological tools used to modulate the channel. Here, we address this issue by synthesising a methylated analogue of the tool KCa1.1 channel activator NS11021. The compound (NS13558) is designed as a structurally closely related and biologically inactive analogue of NS11021. NS13558 did not elicit any significant opening of cloned human KCa1.1 channels, but maintained comparable biological activity towards other cardiac ion channels as compared to NS11021. In isolated perfused rat hearts subjected to ischemia–reperfusion, infarct size was reduced from 29% in control to 7% in NS11021 treated hearts. In comparison, the inactive derivate of NS11021, i.e., NS13558, did not confer any cardioprotection, demonstrated by an infarct size identical to control hearts. This suggests that NS11021 exerts its primary effect through KCa1.1 channels, which indicates an important role of these channels in protection against ischemia–reperfusion injuries. Furthermore, the study demonstrates a novel way of combining an activator of the KCa1.1 channel (NS11021) and its structurally closely related inactive analogue NS13558 to address the functional role of KCa1.1 channels, and we believe these novel tools may constitute a valuable addition to understanding the functional role of KCa1.1 channels under physiological and pathophysiological conditions.     

Nicorandil ameliorates mitochondrial dysfunction in doxorubicin-induced heart failure in rats: Possible mechanism of cardioprotection

Despite of its known cardiotoxicity, doxorubicin is still a highly effective anti-neoplastic agent in the treatment of several cancers. In the present study, the cardioprotective effect of nicorandil was investigated on hemodynamic alterations and mitochondrial dysfunction induced by cumulative administration of doxorubicin in rats. Doxorubicin was injected i.p. over 2 weeks to obtain a cumulative dose of 18 mg/kg. Nicorandil (3 mg/kg/day) was given orally with or without doxorubicin treatment. Heart rate and aortic blood flow were recorded 24 h after receiving the last dose of doxorubicin. Rats were then sacrificed and hearts were rapidly excised for estimation of caspase-3 activity, phosphocreatine and adenine nucleotides contents in addition to cytochrome c, Bcl2, Bax and caspase 3 expression. Moreover, mitochondrial oxidative phosphorylation capacity, creatine kinase activity and oxidative stress markers were measured together with the examination of DNA fragmentation and ultrastructural changes. Nicorandil was effective in alleviating the decrement of heart rate and aortic blood flow and the state of mitochondrial oxidative stress induced by doxorubicin cardiotoxicity. Nicorandil also preserved phosphocreatine and adenine nucleotides contents by restoring mitochondrial oxidative phosphorylation capacity and creatine kinase activity. Moreover, nicorandil provided a significant cardioprotection via inhibition of apoptotic signaling pathway, DNA fragmentation and mitochondrial ultrastructural changes. Interestingly, nicorandil did not interfere with cytotoxic effect of doxorubicin against the growth of solid Ehrlich carcinoma. In conclusion, nicorandil was effective against the development of doxorubicin-induced heart failure in rats as indicated by improvement of hemodynamic perturbations, mitochondrial dysfunction and ultrastructural changes without affecting its antitumor activity.     

Pinacidil uptake and effects in the isolated rabbit heart

The myocardial accumulation of pinacidil showed one-compartment characteristics with a half-time of 1.11 min., whereas the disposition followed three-compartment kinetics with half-times for the relevant two redistributory and the terminal phases of 0.39, 1.51 and 5.44 min., respectively. At a steady-state drug concentration in the perfusate of 6.12 nmol ml-1, the average concentration of pinacidil in the myocardium was 20.6 nmol g-1. The accumulated amount could predictically be referred with 57% to a central and 31 and 12% to two peripheral (deeper) drug pools. The pharmacodynamic effects of pinacidil in the isolated perfused rabbit heart were studied at stepwise increasing concentrations from 0.15 to 100 microM. Coronary flowrate increased initially up to 24.5% at 1.5 microM pinacidil and then gradually decreased. Amplitude and velocity of contraction were both inhibited in a biphasic way up to 92.7 and 94.1%, respectively. Apparent dynamic steady states developed within 13-15 min. The computer-derived inhibitory Em-values related to the first phase were 49.2 and 52.4% and those related to the second phase were 111.7 and 108.3%, respectively. Heart frequency decreased monophasically and exhibited an inhibitory Em-value of 19.6%. Oxygen consumption decreased at pinacidil concentrations higher than 15 microM and the Em-value was 69.7%. The frequency-corrected QT-interval decreased biphasically and the related inhibitory Em-values were 8.6 and 58.7%. The QRS-interval did not change and the PQ-interval only showed a minor increase at the highest pinacidil concentration. Our findings are compatible with the concept of pinacidil being a potassium channel opener.     

Ventricular fibrillation in the isolated rabbit heart

Ventricular fibrillation has been produced in the isolated and perfused rabbit heart by stimulating electrically at a rate from 500 to 700/min. When the perfusion fluid contained normal amounts of sodium, potassium and calcium, the fibrillation persisted after the stimulation was stopped in about 40% of hearts. When the sodium was reduced to half, tonicity being maintained by sucrose or by choline chloride, persistent fibrillation was observed in 100% of hearts. The addition of eserine or of atropine or of carbachol did not alter the percentage of hearts in which fibrillation persisted. The antimalarial compounds chloroquine, mepacrine, and pyrimethamine arrested persistent fibrillation, restoring a normal rhythm.