Fluctuations of membrane potential in isolated single ventricular myocytes of guinea-pig upon resumption of oxidative phosphorylation

Electrical and mechanical activities of guinea-pig single ventricular myocytes were investigated under conditions simulating hypoxia-reoxygenation. The localized movement of sarcomere was recorded simultaneously with membrane potential, and analyzed using microcomputer-based image processing. Exposure to 5 mm CN^- caused progressive shortening of action potential duration and attenuation of twitch contraction. The myocytes became inexcitable about 30 to 70 min after the CN^- treatment. On removal of CN^-, the myocytes exhibited periodic miniature membrane depolarizations from the resting potential level (-95 mV). When depolarizations were smaller than 6 mV in amplitude and longer than 500 ms in duration, they were accompanied by localized sarcomere shortening like a propagating contractile wave (unifocal oscillation). Membrane depolarizations of larger amplitude and shorter duration were associated with a more uniform pattern of localized sarcomere shortening (multifocal oscillation). Trains of electrical stimuli applied during the washing out period caused transient augmentation of potential fluctuation and enhancement of synchronization of sarcomere shortening. These results suggest that non-uniform elevation of intracellular calcium concentration on the resumption of oxidative phosphorylation may initiate oscillatory fluctuations of membrane potential leading to abnormal spontaneous excitation.