Effects of Cell Density and Low K on Action Potentials of Cultured Chick Heart Cells

Hearts from 7-day-old chick embryos were separated by 0.05% trypsin and subsequently cultured in a medium containing low (1.4 mM) and normal (4.4 to 5.6 mM) potassium (K) concentration. A method was developed for controlling environmental conditions (pH, temperature, osmolarity) of 1- to 3-day. old cultured heart cells during intracellular recording with microelectrodes. No apparent differences were noted in the measurement of the several components of the action potential as a function of incubation time. Action potential configurations recorded from cells in dense areas of a culture were noticeably different from those potentials obtained in sparse areas of the same culture; the latter were similar to those of the slowly conducting cardiac junctional tissues. This difference was observed both in the presence of normal and low K. The transmembrane potential recorded from cells in densely populated areas in the normal K medium was characterized by large amplitude and steady, high resting potential whereas that recorded from cells in similar areas in the low K medium had a small amplitude, low resting potential and prominent diastolic depolarization. The tissue cultured in low K also showed a tendency to fibrillate and spontaneously defibrillate.