EFFECT OF ACETYLSTROPHANTHIDIN ON ACTION-POTENTIAL DURATION AND RELATION WITH EXTRACELLULAR POTASSIUM IN SHEEP ISOLATED PURKINJE-FIBERS

AIM: To study the relation between the effect of acetylstrophanthidin on action potential duration ( APD) and the extracellular potassium co ncentration. METHODS: Effect of acetylstrophanthidin (AS 0.15 mmol.L-1 ) on APD at different extracellular potassium concentrations was studi ed at the stimulation cycle lengths of 990 and 690 ms in sheep isolate d cardiac Purkinje fibers using the standard microelectrode technique. RESULTS: At [K+](o) 4.0 mmol.L-1, the biphasic effect of AS on APD ap peared obviously. Both APD(50) and APD(90) were lengthened within the first 10 min of drug exposure. After 10 min, they were shortened at al l pacing cycle lengths. On the other hand, at [K+](o) 5.4 mmol.L-1, AS only shortened APD markedly without lengthening effect on it. The bip hasic and monophasic effects of AS on APD were found at [K+](o) 4.0 mm ol.L-1 and 5.4 mmol.L-1, respectively. CONCLUSION: The effect of AS on APD was related to the concentration of [K+](o).