Effects of the calcium antagonist gallopamil on the increase of myocardial extracellular potassium activity during LAD occlusion in dogs

Summary It has been implied that the increase of myocardial extracellular potassium activity ([K⁺]_c) in the early stage of acute myocardial ischemia is a major cause of the increased likelihood of arrhythmia after acute coronary artery occlusion. There is also experimental evidence that some calcium antagonists reduce the occurrence of ischemia-induced early ventricular arrhythmias. In order to clarify the antiarrhythmic effect of gallopamil during the early phase of acute LAD occlusion, the influence of this calcium antagonist on the time course of [K⁺]_c during acute ischemia was measured in open-chest anesthetized dogs using a K⁺-selective surface multielectrode. The regional myocardial blood flow was determined with 9 m radioactive tracer microspheres.After application of gallopamil (bolus, 25 g/kg and infusion 2.5 g/kg·min for 30 min) the maximal and mean rate of rise of [K⁺]_c as well as the plateau of [K⁺]_c reached during ischemia were significantly diminished compared with the control occlusions. 90 min after gallopamil, the rate of rise of [K⁺]_c as well as the plateau of [K⁺]_c reached were still significantly reduced, but 180 min after the gallopamil application, no significant differences between the time course of [K⁺]_c and that of the two control occlusions could be found. Gallopamil significantly elevated, myocardial blood flow in the non-ischemic area, but did not influence blood flow in the ischemic region.While collateral perfusion remains unchanged, the slowed and reduced increase of myocardial [K⁺]_c during acute coronary artery occlusion may be an important component of the antiarrhythmic effect of gallopamil during early ischemia.Preliminary results were presented at the International Symposium on Calcium entry blockers and tissue protection, Rome, 1984, at the 59th Meeting of the Deutsche Physiologische Gesellschaft, Dortmund, 1984, at the 50th meeting of the Deutsche Gesellschaft für Herz- und Kreislaufforschung, Mannheim, 1984, and at the IXth European Congress of Cardiology, Düsseldorf, 1984.     

Three-dimensional analysis of regional mechanical function,blood flow and electrophysiological parameters during early myocardial ischemia in dogs

Summary Ventricular arrhythmias are primarily responsible for sudden cardiac death early after the onset of acute myocardial ischemia. We designed an experimental model to simultaneously characterize regional myocardial function, myocardial blood flow, and electrophysiological parameters, and to determine predisposing factors for the development of early ventricular arrhythmias (EVA).The left circumflex coronary artery was occluded in six anesthetized (n=2 piritramide/N₂O, n=4 chloralose/urethane) mongrel dogs. Systolic wall thickening (% WT) in a control zone and in the central ischemic zone was measured with sonomicrometry and regional myocardial blood flow (RMBF) with colored microspheres. Excitability and relative refractory period at the stimulus electrode and conduction times to all other electrodes were determined with a three-dimensional transmural multi(16)-electrode array using a computer algorithm.In three of six dogs spontaneous EVA occurred 4 to 6 min after coronary occlusion, degenerating to ventricular fibrillation in two of these dogs. The three dogs developing EVA were not distinguished from those not developing EVA, neither by the kind of anesthesia nor by ischemic % WT (–6.6±3.8 [SD] vs –7.8±1.6, ns). Also, dogs with and without EVA did not differ significantly in excitability and relative refractory period. In contrast, dogs with EVA were characterized by a greater mass of severely ischemic myocardium, i.e., exhibiting a RMBF reduction to less than 0.1 ml/(min · g) (18±3 g vs 7±4 g, p<0.05), and by an increase in subendocardial conduction times of greater than 100% above the respective pre-ischemic values (120±18% vs 66±9%, p<0.05). Dogs with and without EVA were not as clearly distinguished by the increases in subepicardial (81±22% vs 46±15%, ns) and transmural (98±31% vs 67±14%, ns) conduction times.The development of EVA is associated with a greater mass of severely ischemic myocardium and a greater increase in subendocardial conduction times.Dedicated to Prof. Dr. Werner Meesmann on the occasion of his 68th birthday     

Effect of urapidil on the performance of ischemic myocardium in anesthetized dogs

Summary Urapidil (URA) is used to treat acute hypertension in patients with coronary artery disease, but the effect of URA on the performance of ischemic myocardium has not yet been investigated. The present study was intended to assess the function of ischemic myocardium following URA administration. In eight anesthetized (piritramide) open-chest dogs systolic contraction (dL) and end-diastolic length (edL) of myocardium supplied by the left descending (LAD) and circumflex (LCA) coronary arteries were measured by sonomicrometry simultaneously with aortic pressure (AoP), left ventricular end-diastolic pressure (LVedP), heart rate (HR), stroke volume (SV), and LAD-flow (QLAD). QLAD was reduced by LAD stenosis to about 50% of control, decreasing dLLAD by 55%. Concomitantly, edLLAD increased by about 9% and LVedP by 22%, whereas AoP decreased by 5%. Then, URA was given i.v. (0.25+0.25+0.50+1.0 mg/kg) in 15-min intervals. Following URA, the performance of the non-ischemic area was not systematically affected, but dLLAD increased by about 50%. This could neither be related to the significant reduction in afterload (AoP: –8%), nor to an increase in preload (LVedP and edLLAD did not change significantly), nor to an improved oxygen supply via the LAD (QLAD even decreased), although an increased collateral flow from the LCA could not be excluded. The increase in systolic shortening correlated very closely to a decrease in heart rate (r=–0.92). It is concluded that the improved function of ischemic myocardium following urapidil resulted from a reduced oxygen demand in consequence to the decrease in heart rate.     

Atrial and ventricular myosins from human hearts II. Isoenzyme distribution after myocardial infarction

Summary Human atrial and ventricular myosins were prepared from autopsy specimens from subjects with coronary heart disease. Cardiac myosin light chain isotypes were resolved using twodimensional gel electrophoresis, whereas myosin isozymes were detected by pyrophosphate gel electrophoresis.Myocardial infarction and associated work overload cause a transition in the light chain complements of the myosins. Thus ventricular myosin light chains were found in pressure overloaded atria and atrial light chains have also been identified in the infarct ventricle of the human heart.Two molecular isoenzymes of the human atrial myosin, the relative proportions of which are changed after infarction, were separated under non-dissociating conditions by gel electrophoresis. A decrease in HA-3 and a corresponding increase in HA-1 were observed. Ventricular hypertrophy in patients with coronary insufficiency induces a second ventricle isomyosin, called HV-1, with the same electrophoretic mobility as HA-1. The relative part of this myosin type amounts to 20%. Comparative peptide mapping studies were carried out on myosin subfragment-1 preparations from normal and infarct ventricles. In the primary structures, the chymotrypsic digestions produced slight differences.These data demonstrate the heterogeneity of human atrial and ventricular myosins in patients with coronary heart disease.     

Three-dimensional distribution of collateral blood flow within the anatomic area at risk after circumflex coronary artery occlusion in dogs

Summary It is generally accepted that occlusion of a major coronary artery in the dog results in a transmural gradient of collateral blood flow, with the subepicardial region receiving the greatest perfusion. The lateral and base to apex distribution of collateral blood flow and of metabolic and functional consequences of ischemia have been more difficult to define. One reason for such difficulties has been the failure to define the anatomic boundarics of the ischemic vascular bed so that uncontaminated samples of ischemic and non-ischemic tissue could be selected for study. In the present study, the three dimensional distribution of myocardial blood flow during occlusion of the circumflex artery was mapped in seven dogs. At the end of the study, the boundaries of previously ischemic and non-ischemic regions were identified by simultaneous coronary perfusion with red and blue dyes. Left ventricular slices were separated into ischemic and non-ischemic vascular beds based on the dye boundarics, with 1–2 mm of tissue trimmed from this interface to eliminate visually apparent admixture. The ischemic vascular bed of each cross sectional slice then was cut into five transmural wedges, each 3–5 mm wide; each wedge was further subdivided into subendocardial, middle, and subepicardial thirds. The results of blood flow measurements in these samples indicate that the dye injection technique identifies a real interface with a sharp lateral transition in blood flow between ischemic and non-ischemic vascular beds. Within the ischemic vascular bed, there is a transmural gradient of collateral blood flow, but within a given mural layer, there is no consistent gradient from the center to lateral edge or from base to apex of the ischemic region. Thus, in studies designed to characterize the properties of myocardium on either side of the ischemic/non-ischemic interface, reasonable resolution can be achieved by coronary dye infusions to permit visual identification of this interface. On the other hand, in studies in which collateral blood flow is measured as a baseline predictor of infarct size, measurements can be made in a central ischemic block which will be representative of most or all of the ischemic region. Borderzone samples can be excluded to avoid contamination of ischemic samples with non-ischemic tissue.Supported in part by NIH grants 27416 and 23138.     

Enhanced membrane protein kinase C activity in myocardial ischemia

Summary The protein kinase activity in cytosol was similar in control, ischemic, and reperfused hearts; however, a 1.5-fold increase in membrane protein kinase activity was induced by ischemia and reperfusion. The H-7 inhibitable cytosolic protein kinase activity decreased by 40% with 30 min ischemia, while that of membrane fraction increased 1.8-fold. However, the CGS9343B inhibitable protein kinase activity in cytosolic fractions was unaffected by ischemia, while that of membrane increased by about 1.7-fold. These results suggest that myocardial ischemia is associated with enhanced protein kinase C and calmodulin-dependent kinase activities in membrane fraction. Furthermore, the results also suggest a translocation of protein kinase C activity from the cytosol to the membrane. Reperfusion of ischemic myocardium did not result in any further increase of protein kinase C and calmodulin-dependent kinase activities in the membrane. These enhanced protein kinase activities also resulted in an enhanced phosphorylation of endogenous membrane proteins. The creatine kinase released from the heart was increased by both ischemia and reperfusion. Therefore, these results suggest that biochemical cascades of reactions caused by enhanced membrane protein kinase C and calmodulin-dependent kinase activities may contribute to ischemic-reperfusion injury.     

Effects of dipyridamole on collateral flow and regional myocardial function in conscious dogs with newly developed collaterals

Summary Studies were conducted on six conscious dogs instrumented for measurement of subendocardial segment lengths in the area perfused by the left anterior descending coronary artery (LAD) and left circumflex coronary artery (LCCA), LCCA flow, and left ventricular pressure. Externally inflatable occluders were placed around the proximal LAD and LCCA. Collateral channels sufficient for the resting metabolic demands in the occluded LCCA perfusion territory were induced by repeated, brief LCCA occlusions. Dogs were then subjected to two consecutive brief periods of LAD occlusion. Dipyridamole (0.25 mg/kg) was injected intravenously 3 min prior to the second LAD occlusion. The collateral blood flow from the LCCA to the occluded LAD area was measured as the stepwise decrease in LCCA flow upon release of the LAD occlusion. During LAD occlusion after dipyridamole treatment collateral blood flow velocity decreased to 3.8±1.1 cm/s (±standard error) compared with a value of 4.9±0.9 cm/s measured during LAD occlusion without dipyridamole treatment. Percentage systolic segment shortening in the collateral dependent zone significantly deteriorated from 14.3±5.2 to 9.7±5.0% (p<0.05). Electrocardiograms taken simultaneously from endocardial ultrasonic transducers in the ischemic segment revealed significant increases in ST-segment level from 4.2±0.6 to 5.4±0.6 mV. These findings indicate that dipyridamolc adverscly affects the extent of myocardial ischemia in the collateral-dependent zone.Supported by grant HL 32800 from the NHLBI     

Superoxide dismutase and catalase do not improve recovery of regional myocardial contractile function when given at the time of reperfusion after reversible regional ischemia in anesthetized dogs

Summary Earlier studies have demonstrated an improvement in the recovery of the regional myocardial function after reversible myocardial ischemia when dogs were treated with superoxide dismutase (SOD) + catalase (CAT). In all these studies, drug administration was started prior to the ischemic period. The aim of this study was to investigate the effects of SOD and CAT on the recovery of the regional contractile function in anesthetized beagle dogs when the drugs were administered at the time of reperfusion. The animals were subjected to 20 min of left coronary artery occlusion followed by 3 h reperfusion. The regional myocardial contractile function, measured as subendocardial segment shortening (SS, sonomicrometry) decreased to below zero and the regional blood flow in the ischemic subendocardium was reduced to about 5 % of pre-ischemic values during the coronary artery occlusion period. The size of the occluded bed was similar in the two groups. Saline (n = 8) or SOD (10 mg/kg) + CAT (3.4 mg/kg) (n = 8) were infused into the left atrium from 2.5 min prior to until 20 min after the start of reperfusion. The peak plasma level of SOD was 102 ± 15 mg/1 at 20 min reperfusion. There were no significant differences in the arterial blood pressure, cardiac contractile function and regional blood flow between the two groups at any time during the experiment. During reperfusion in the dogs given vehicle, SS recovered to 48 ± 7 % (mean ± SEM) after the first hour of reperfusion, and to 51 ± 6 % of pre-ischemic values after 3 h of reperfusion. The corresponding values in SOD + CAT treated dogs were 50 ± 5 % (1 h) and 53 ± 8 % (3 h), respectively. It is concluded that SOD + CAT, when given at the time of reperfusion, did not improve the regional contractile function after reversible ischemia in the anesthetized beagle dog.     

Acute hemodynamic effects of coronary artery ligation in conscious rats

Summary Because of the growing interest in the use of coronary artery ligation (CAL) in rats as a model for studies on heart failure, we have investigated the acute hemodynamic changes following CAL in conscious rats.Animals were equipped for measurement of cardiac output (CO), arterial pressure (MAP), and central venous pressure (CVP). These parameters were measured before CAL, immediately after, and 24 h after. Furthermore, peak CO, obtained by rapid infusion of 12 ml Ringer's solution (in 1 min) was measured 2 days before and 1 day after CAL.CAL resulted in immediate reduction of CO, because of reduced stroke volume (SV). CO as well as SV were inversely correlated with infarct size as determined 24h after CAL. Heart rate (HR) and MAP did not change. Twenty-four hours later, CO was still reduced. MAP was now reduced, possibly as a result from resetting of nervous reflex mechanisms.Before CAL, peak CO and SV were similar in CAL and sham animals. At 24 h after CAL, these parameters were greatly reduced in CAL rats. Peak values were strongly correlated to infarct size.Results indicate that CAL in rats leads to hemodynamic changes similar to the ones observed following myocardial infarction in man. Cardiac function is related to infarct size and is altered both at rest and during maximal stimulation.J. F. M. Smits is an Established Investigator for the Netherlands Heart Foundation     

Early changes in collateral blood flow to ischemic myocardium and their influence on bimodal vulnerability during the first 30 min of acute coronary artery occlusion in dogs

Summary Coronary collateral blood flow and its changes during the first 30 min of acute coronary artery occlusion were studied in 34 anesthetized dogs to clarify its influence on the vulnerability of the heart in this first arrhythmic phase. Collateral flow was determined with 9-m tracer microspheres (TM) injected at 1, 10 and 30 min after acute proximal occlusion of the left circumflex (LCX, n=30) or left anterior descending (LAD, n=4) coronary artcry. The post-mortem selective retrograde coronary angiography was used to evaluate the functional extent of preexisting coronary collaterals.After acute LCX occlusions collateral flow increased significantly (p<0.05), from 17.8±2.7 ml·(min·100 g)^–1 at 1 min to 29.3±5.1 ml·(min·100g)^–1 at 30 min of occlusion in animals with well-formed precxisting coronary collaterals (group 1), whereas it was very low (4.7±0.6 ml·(min·100 g)^–1; n=13) and changed only slightly in dogs with poor collaterals (group 2). Most of these animals died by ventricular fibrillation (VF) before a second measurement could be carried out. In four dogs with poor collaterals but an unusually small LCX area (group 3), flow remained almost constant (11.0±4.7 versus 11.0±4.4 ml·(min·100 g)¹) during this period. Similar results were obtained in animals with acute LAD occlusion (group 4).Ventricular extrasystoles (VES) mainly developed in animals with poor collaterals and respective low and almost unchanging collateral flow (group 2, 3, 4) while none or only a few VES occurred in dogs in which flow initially was clearly higher and increased significantly (group 1). The animals of group 1, 3 and 4 all survived the first arrhythmic phase, whereas all the animals of group 2 died by VF, either in the arrhythmic subphase Ia (n=7) or Ib (n=6). The results of the present study show that only the initial magnitude of flow is decisive for the development of VES and VF during the first arrhythmic phase, whereas the subsequent increase in flow is of no importance to the bimodal vulncrability in the first arrhythmic phase (subphases Ia and Ib). The in vivo measured cirtical minimal collateral flow of about 5 ml·(min·100 g)^–1 corresponds well with the survival limit (border between collateral state III and IV) previously determined by post-mortem retrograde coronary angiography.Supported by the Minister für Wissenschaft und Forschung des Landes NRW, F.R.G.These results were presented in part at the meeting of the German Physiologic Society, Gießen, 1982, the meeting of the German Society of Heart- and Circulation Research, Bad Nauheim, 1982, and the IXth European Congress of Cardiology, Düsseldorf, 1984.     

Mitochondrial respiration in myocardial biopsy samples as a criterion of postischemic recovery of the cardiac contractility

Summary Isolated perfused guinea pig hearts were arrested by a high K⁺ cardioplegic solution containing (PG group) or lacking (control group) 10 mM phosphocreatine +15 mM glutamate. Total normothermic ischemia lasted 45 min followed by 30 min reperfusion. Mitochondrial respiration in the absence and presence of different concentrations of ADP and creatine was studied in biopsy samples (6–8 mg) after saponin treatment. The samples were taken before and after ischemia, as well as after the reperfusion period. A slightly better relative recovery of developed pressure (RRDP) in PG group was associated with higher mitochondrial acceptor control ratio after reperfusion (5.74±0.32 vs. 4.54±0.21 in PG and control groups, resp., p<0.01). When the results obtained in both groups were treated together, tight correlations between the pre- or postischemic mitochondrial state and RRDP were revealed. Higher values of RRDP were found for the hearts with lower preischemic values of (low ADP+creatine)-stimulation of mitochondrial respiration (r=–0.57, p<0.01). Relative changes in this mitochondrial parameter during ischemic period were in a good correlation with the RRDP (r=0.82, p<0.001). The data suggest that the study of the mitochondrial function in myocardial biopsy samples before ischemia and reperfusion could provide a useful information for the prognosis of cardiac function recovery.     

Ultrastructural damage and Ca2+-shifts in the canine myocardium subjected to regional incomplete ischemia

Summary The role of Ca²⁺ in the pathogenesis leading to ischemic myocardial cell death is still controversial. To gain insight into this phenomenon a cytochemical procedure, the phosphate pyroantimonate method, was used to localize different subcellular Ca²⁺-pools at the ultrastructural level. After 45 min of left anterior descending coronary artery (LAD) occlusion, the coronary arteries were perfused with triphenyltetrazoliumchloride staining (TTC) to identify viable ischemic and infarcted tissue. In non-ischemic tissue, Ca²⁺-deposits were confined to the sarcolemma, sarcolemma-derived vesicles, transverse tubules, and intercalated disks. In infarcted tissue (TTC-negative), the sarcolemma lost its Ca²⁺-binding capacity and mitochondria were either overloaded with Ca²⁺-precipitate or they contained amorphous densities. In viable ischemic areas (determined with the TTC-technique) the sarcolemma was virtually devoid of Ca²⁺-deposits. Mitochondria in this area frequently showed clumping of the cristae, associated with an accumulation of Ca²⁺-precipitate in between the clustered cristae. The results of this study indicate that Ca²⁺-shifts occur in ischemic myocardial cells before the occurrence of other ultrastructural signs of irreversible injury which, therefore, narrows the possibility that Ca²⁺-overload is only a consequence of ischemic cell death.     

Quantification of the total Na,K-ATPase concentration in atria and ventricles from mammalian species by measuring3H-ouabain binding to intact myocardial samples. Stability to short term ischemia reperfusion

Summary Na,K-ATPase concentration was measured by vanadata facilitated³H-ouabain binding to intact samples taken from various parts of porcine and canine myocardium. In porcine and canine heart³H-ouabain binding site concentration in ventricles was 1.4–2.5 times larger than in atria. Evaluation of³H-ouabain binding kinetics revealed no major difference between atria and ventricles: Equilibrium was obtained after the same incubation time in right atrium (RA) as in left ventricle (LV), both in porcine and canine heart. Unspecific uptake and retention of³H-ouabain was for porcine heart RA and LV 1.5 and 1.4, respectively, and for canine heart RA and LV, both 1.2% filling (i.c., volume (ml) of incubation medium³H-radioactivity taken up per mass unit (g wet wt.) of tissue multiplied by 100). The apparent dissociation constant (K _d ) was 1.4×10^–8 and 1.9×10^–8 in porcine RA and LV and 2.6×10^–8 and 6.1×10^–8 mol/l in canine RA and LV. Loss of specifically bound³H-ouabain during the washout procedure occurred with a half-life time (T_1/2) of 16.7 in RA and LV of porcine heart and 91.2 and 151.6h in RA and LV of canine heart. Duly corrected for these errors of the method-factor 1.16 and 1.13, respectively, for porcine RA and LV, and factor 1.11 and 1.13 for canine RA and LV, total³H-ouabain binding site concentration was found to be 553±74 and 1037±45 pmol/g wet wt. (means±SEM, n=5) in porcine RA and LV, and 569±37 and 1410±40 pmol/g wet wt. (means ±SEM, n=5) in the canine RA and LV. These values were confirmed by measurements of³H-digoxin binding to the porcine heart. The present quantification of myocardial Na, K-ATPase gives values up to 154 times higher than measurements based upon Na,K-ATPase activities in membrane fractions where the recovery of Na,KK-ATPase may be less than 1% due to loss during purification. A higher Na,K-ATPase concentration is found in small animals than in large animals. A relationship between higher concentration of Na, K-ATPase and larger pressure work in ventricles compared to atria is suggested. Myocardial³H-ouabain binding sites were found to be stable for 20 min of ischemia, followed by 1h of reperfusion, supporting the concept that myocyte injury induced by short term ischemia may be reversible and that reperfusion may result in normalization.     

The effect of calcium concentration on spontaneous ventricular defibrillation and VF threshold

Summary In order to investigate the influence of the effective refractory period on spontaneous ventricular defibrillation, isolated rat hearts were perfused with Krebs-Henseleit solution containing 0.5, 2.7 and 5.1 mM calcium. After measuring the fibrillation threshold at spontaneous rate (SR), ventricular fibrillation (VF) was induced during basic ventricular pacing of 110% SR, or the highest rate permitting 11 electromechanical coupling. The VF threshold was significantly reduced from 13.6±3.5 to 7.9±5.3 and 5.1±3.4 mA at 0.5, 2.7 and 5.1 mM Ca⁺⁺ concentrations, respectively. The incidence of spontaneous recovery from VF, induced during basic pacing, was 100%, 83% and 50% at calcium concentrations of 0.5, 2.7 and 5.1 mM, respectively, (p<0.01 for the incidences at 0.5 mM versus 5.1 mM Ca⁺⁺). The incidence of spontancous defibrillation decreased when the hearts were driven rapidly, with spontaneous recovery rates of 92%, 58% and 0% (p<0.0001)) for corresponding increases in Ca⁺⁺ concentration. Induced ventricular fibrillation of fine morphology was frequently observed at 5.1 mM Ca⁺⁺. It appears that progressive impairment of spontaneous defibrillation is caused by an increase in calcium concentration, this effect being more pronounced at high ventricular rates. Variations in the effective refractory period, caused by alterations in extracellular calcium concentration and differences in intracellular Ca⁺⁺ accumulation, may account for the above results.     

Atrial and ventricular myosins from human hearts. I. Isoenzyme distribution during development and in the adult

Summary Two distinct types of native isomyosins, referred to as human fetal HF and human ventricular myosin HV-3, have been identified in the human fetal heart during two different periods of gestation and in the neonatal state, whose relative parts change with development. In the adult ventricle, only HV-3 was found. Two myosin isoforms designated as HA-3 and HA-1 occur in the atrial myocardium of the normal human heart, which are electrophoretically distinct from the fetal isoenzymes.In fetal tissue, the myosin light chain complement is composed of atrial and ventricular light chains. In support of recent results, we also found identical spots from the atrial ALC-1 and the fetal light chain FLC, suggesting a homology between them. Apart from the light chains typical for this tissue, the atrial myocardium also contains ventricular light chains. Therefore we hypothesize that atrial myosin consists of two atrial isoenzymes and presumably of a ventricular type, too.Differences between atrial and ventricular myosin from human hearts were demonstrated by measuring the temperature dependence of the Ca²⁺-ATPase.     

Effects of acute iron loading on contractility and spontaneous beating rate of cultured rat myocardial cells

Summary Cardiac dysfunction is a well known but poorly understood complication of iron overload. We have previously shown that cultured myocardial cells are able to assimilate large amounts of iron. In the present study, the effect of iron on the rate and amplitude of beating in monolayer cultures of rat ventricular myocytes was studied. Iron had negative chronotropic and inotropic effects, both reversible upon washout. The negative chronotropic effect developed earlier and could be reversed by adrenaline. The negative inotropic effect took longer to develop and was completely reversed by caffeine. Elevated [Ca⁺⁺] also partially restored impaired contractility, while adrenaline or ouabain did not show any significant effect. These results indicate that iron toxicity in cultured heart cells impairs cellular function at both sarcolemmal and intracellular sites.     

Enhanced myocardial preservation by nicotinic acid,an antilipolytic compound: Mechanism of action

Summary The cardioprotective effects of an antilipolytic compound, nicotinic acid, on arrested-reperfused myocardium were investigated in the isolatedin situ pig heart preparation. Hearts were preperfused for 15 min in the presence of (5-³H)-glucose and (U-¹⁴C)-palmitic acid. Half of the hearts were then perfused with 0.08 mM nicotinic acid for an additional 15-min period, while the remaining control hearts received unmodified perfusion. Arrest was then induced in all animals for 2 h using hypothermic K⁺ cardioplegia, followed by 60 min of normothermic reperfusion. In control hearts, there were significantly greater levels of long-chain acyl Co-A and acyl carnitine and lower levels of membrane phospholipids than in the nicotinic acid group. While nicotinic acid inhibited -oxidation during pre-ischemia and reperfusion, it also prevented the degradation of membrane phospholipids. The net result was a reduction of free fatty acid accumulation during arrest and reperfusion in the nicotinic acid group. Glycolysis, as reflected in³H₂O production, was significantly increased by nicotinic acid administration. In the control heart as compared to the nicotinic acid group, the incorporation of¹⁴C-label from palmitate into triglyceride and cholesterol during arrest was enhanced, while incorporation into phospholipids was depressed. The cardioprotective effects of nicotinic acid were demonstrated by decreased release of creatine kinase and improved coronary blood flow, and cardiac contractility in the reperfused myocardium supplemented with nicotinic acid compared to the control group. These results suggest that nicotinic acid significantly protects the arrested-reperfused myocardium by a) preventing elevation of myocardial fatty acid levels, b) stimulating glycolysis by limiting fatty acid oxidation, c) inhibiting degradation of membrane phospholipids, and d) preventing accumulation of fatty acid metabolites with harmful detergent properties.Supported by NIH Grants HL22559-06, HL33889 and HL34360, and American Heart Association Grant 11-202-856.Presented at the 72nd Annual Clinical Congress, American College of Surgeons, Surgical Forum, New Orleans, October 1986.     

Voltage-dependent calcium release in guinea-pig cardiac ventricular muscle as antagonized by magnesium and calcium

Summary An increase in extracellular potassium concentration from 4 to 16 mmol/l caused a decrease in membrane potential from –92 to –59 mV and selectively diminished the earlier of two contraction components of guinea-pig papillary muscles at 0.2 Hz stimulation frequency in the presence of noradrenaline. The influence on the early contraction component had a threshold of 8 mmol/l K⁺, corresponding to a membrane potential of –77 mV. However, test contractions elicited 800 ms after the 5 s stimulation interval exhibited an unimpaired early component. Since the activator calcium responsible for the early contraction component is derived, in mammalian ventricular muscle, from the junctional sarcoplasmic reticulum (20), it is assumed that the release site of the reticulum was filled with calcium shortly (800 ms) after a regular contraction, and lost its calcium at 16 mmol/l extracellular K⁺ during the 5 s stimulation interval. The potassium-induced depolarization determined the rate of calcium leakage during rest from the intracellular store. The depolarization-induced decline of the early contraction component was equally well antagonized by Mg²⁺ or Ca²⁺ without influencing the measured transmembrane potential. Both divalent cations shifted the relation between potassium concentration or membrane potential and the strength of the early contraction component to less negative membrane potentials. In order to reduce the early contraction component by 25% in the presence of 9.6 instead of 1.2 mmol/l Mg²⁺, the potassium concentration had to be increased from 9.6 to 22.0 mmol/l, with a respective decrease in resting membrane potential from –72.6 to –51.1 mV. The antagonistic effect of both divalent cations is thought to result from the neutralization of negative charges outside the sarcolemma with a respective decrease in the outside surface potential.     

The electrophysiology of cardiac allograft rejection: Independent effects of rejection and perioperative ischemia on the sinus node recovery phenomenon after cardiac transplantation

Summary We characterized the effect of cardiac allograft rejection on the sinus node (SN) recovery response from overdrive suppression. A total of 54 corresponding data sets (SN recovery time [SNRT]/endomyocardial biopsy [EMB]) was available in 24 transplant recipients with normal SNRT. Data were pooled in the rejection vs the no-rejection group (n=16 vs n=38, respectively).During cardiac rejection (defined as a 7-day period starting 3 days prior to and lasting until 3 days after the EMB) the SNRT curves were moderately, but significantly shifted towards higher values (F=13.4, p=.0003). All changes occurred within accepted normal limits for the SNRT. Multivariate analysis indicated independent effects of donor heart ischemic time (p=.0005) on SNRT in addition to that of rejection. After accounting for that influence of ischemic time respective F values regarding the influence of rejection on the SNRT excursions were 10.8 (ischemic time<100 min, p=.0014) and 4.36 (ischemic time100 min, p=.039).This study shows that cardiac allograft rejection significantly delays the SN recovery response from overdrive suppression. These changes, however, are subtle and, hence, are an unlikely explanation for the often grossly abnormal postoperative SN function.     

Causative role of coronary microvessels for the development and progression of chronic myocardial lesions in spontaneously hypertensive rats (SHR)

Summary The pathomechanisms responsible for the development and progression of myocardial alterations in hypertensive heart disease are largely unknown. Using newly developed preparation and measuring procedures in 78 SHR and 82 controls aged 3–78 weeks, topological relations were detected between focal morphological appearances of chronic myocardial ischemia (fml.) and pathological microvessel (mv.) reactions characterized by morphometric signs of chronic contractions. The smallest ramifications are of particular pathogenic importance. A generalized peak of pathological mv. reactions between the 16th and 24th weeks is responsible for the development of first fml. The further progression of the area density of fml. from 1.26±0.85% (24th week) to 31.82±8.60% (78th week) is attributable to the further increase in pathological mv. reactions caused by organ-specific influences. The histological and morphometric findings suggest that the pathological mv. reactions are aggrevated by their own effects at the local level.Abbreviations d diameter - fml focal myocardial lesions - mv microvessel(s) - SDH succinodehydrogenase