digitonin and Coronary-Disease

Topics: Animals; Calcium; Coronary Disease; Digitonin; Mitochondria, Heart; Myocardial Contraction; Myocardium; Oxygen Consumption; Potassium; Sodium

ATP-dependent, inorganic phosphate-supported 45Ca2+ uptake by digitonin-lysed adult rat ventricular cardiomyocytes was used to evaluate the effects of simulated ischemia and reperfusion on the physically intact sarcoplasmic reticulum. Mitochondrial reactions were inhibited with rotenone and oligomycin. 45Ca2+ accumulation in the presence of the calcium efflux inhibitors, procaine (10 mM) and ruthenium red (30 microM), was used to characterize unidirectional uptake kinetics. A decrease in pH from 7.2 to 6.6 increased the [Ca2+] K0.5 from 0.5 to 2.0 microM and reduced the apparent Vmax by 28%. In the absence of procaine and ruthenium red, at a free [Mg2+] of 0.5 mM, maximum net uptake occurred at pCa 6.2 when pH was 7.2 and at pCa 6.0 when pH was 6.6. At lower pCa, net Ca2+ accumulation declined. Increasing free [Mg2+] from 0.5 to 1 mM at pH 6.6 or to 2.5 mM at pH 7.2 increased net 45Ca2+ accumulation in the absence of procaine and ruthenium and shifted maximum uptake to pCa 5.6 and 6.0, respectively. Increases in cytosolic free [Mg2+] thought to occur during myocardial ischemia are therefore capable of inhibiting calcium efflux from the sarcoplasmic reticulum. Reducing [ATP] from 10 to 1 mM reduced maximum net 45Ca2+ uptake by 30% both in the presence and absence of efflux inhibitors. Preincubation of intact myocytes under conditions designed to simulate ischemia and reperfusion decreased 45Ca2+ uptake greater than or equal to 50%. The data indicate that myocardial ischemia and reperfusion can alter both Ca2+ accumulation and calcium release by the sarcoplasmic reticulum.

Topics: Animals; Calcium; Coronary Disease; Digitonin; Heart; In Vitro Techniques; Male; Myocardial Contraction; Myocardial Reperfusion; Myocardium; Rats; Rats, Inbred Strains; Sarcoplasmic Reticulum

Several studies have reported a linear correlation between ATP levels, measured on isolated adult heart cells exposed to anoxia, and cellular configuration. The case is presented here for the viewpoint that these results can best be explained by an asynchronous decline in cellular ATP levels. By asynchrony we mean that an individual cell maintains a constant high level of ATP for a lag period until some point when, over a short period of time, the ATP level suddenly drops to near zero; the time spread of the decline in total measured ATP then arises from a spread in lag periods amongst the cells. By contrast, the synchronous view assumes that the time spread of the decline in total measured ATP reflects the simultaneous slow decline of ATP levels within each cell. These viewpoints have important consequences for elucidating the etiology of cell death.

Topics: Adenosine Triphosphate; Animals; Cell Separation; Coronary Disease; Digitonin; Hypoxia; Myocardial Contraction; Myocardium; Oxygen; Rats; Sarcolemma; Time Factors

Topics: Animals; Carbon Dioxide; Carbon Tetrachloride Poisoning; Coronary Disease; Creatine Kinase; Digitonin; Liver; Malates; Male; Myocardium; Perfusion; Rats; Succinates