Electrical activity of rat myocardial cells in culture: La3+-induced alterations.

Intracellular analysis of neonatal rat (1-2 day old) ventricular cells in culture shows that contracting myocardial cells exhibit an array of different patterns of spontaneous electrical activity. Resting membrane potentials varied between -40 mV and -98 mV. Our results indicate that some cultured cells show resting membrane potentials, overshoot, and total spike amplitude values comparable to those normally found in neonatal and adult rat heart. A low ratio of pacemaker (40%) to nonpacemaker cells (60%) and low incidence of hyperpolarizing after-potentials (35%) were found. La3+ application (0.1-4.0 mM) induced progressive cell depolarization, concomitant diminution in discharge frequency, and marked alteration of action potential configuration. A parallel decline in frequency and strength of rhythmic contractions was observed. Abolition of contractility occurred only in association with depolarization and complete disappearance of action potentials. Recovery of electrical and contractile activity followed medium replacement. Our results indicate that La3+ does not act as a specific excitation-contraction (E-C) uncoupler in the cultured cells but has multiple effects upon their normal electrical characteristics.