Effects of membrane current on transmembrane potentials of cultured chick embryo heart cells

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Abstract
Two to eleven days after myocardial cells were explanted to cultures from the ventricles of 4-day chick embryos two microelectrodes were inserted into a cell cluster. There was no detectable damage to the membrane. Current was passed through one electrode and the membrane potential was measured with the other. Since membrane current density is roughly uniform in nearly spherical cells, the membrane time constant could be directly estimated. The mean value of 17 measurements of the time constant was 35 ± 1 msec. As expected, strong depolarizing current stopped spontaneous contractions and weaker current increased the rate of contraction. Hyperpolarizing current decreased the rate. Break of a hyperpolarizing current nearly always initiated an action potential in both active and quiescent cells. On the basis of these preliminary results, voltage clamping at least of the plateau phase appears feasible in tissue cultures of myocardial cells.