Calcium dynamics in cultured heart cells exposed to defibrillator-type electric shocks

Abstract

Spatial and temporal changes in intracellular calcium ion concentration and transmembrane voltage were recorded optically from single-isolated cultured chick-embryo heart cells exposed to high-voltage, defibrillator-type shocks. Fluorescence changes were measured during 5 msec electric shocks of field strengths up to 56 volts cm in single myocytes stained with a Ca ++-sensitive or voltage-sensitive dye. Shocks caused a reversible period of depolarization, elevated cytosolic Ca ++, and refractoriness. Intracellular Ca ++ elevation had two temporal phases: first, a Ca ++ spike with morphology independent of shock intensity; and second, a prolonged Ca ++ elevation with a shock-intensity-dependent magnitude and duration, and with greatest Ca ++ elevation at the poles of the cell adjacent to the electrodes. The prolonged elevation (second phase) was initiated earlier at the anode-facing pole of the cell than at the cathode-facing pole. These results suggest that postshock Ca ++ entry consists of two parts: early normal entry through excitation channels plus a prolonged elevation which may be related to cellular damage.