Hearts (ventricles) from 6- to 8-day-old chick embryos were cultured 1–7 days. Single cells reassembled into various communities of cells which usually contracted synchronously. Many cells were spontaneously active; quiescent cells could be driven. The average magnitude of the action potentials after microelectrode sealing was 71.2 ± 1.5 mv (range of 40–108 mv) and that of the resting potentials 59.0 ± 1.2 mv (range of 40–84 mv). Maximum velocity of depolarization varied between 1–5 v/sec and positive afterpotentials of 6–10 mv were often found. The duration of the action potential varied between 150–500 msec. Plateaus were observed in only a few of the cells; often a second component appeared on the repolarization phase of the spike. Many cells had pacemaker potentials of about 10 mv. However, even though pacemaker potentials were present, many cells were fired by transmission of excitation from neighboring cells; in such cases, a prepotential was generally observed as a step in the rising phase of the action potential. The data from trypsin-dispersed cells were compared with those of nondispersed clumps and with noncultured intact embryonic hearts. The results indicate that the electrophysiological properties of trypsin-dispersed cultured myocardial cells are similar to those of cells in intact embryonic or adult hearts.

Trypsin-dispersed cells from heart (ventricles) of 7- to 8-day chick embryos and 6-day posthatched chicks were cultured 2–15 days. The isolated single cells became attached to the bottom of the culture dish and reassembled into various monolayer communities; the cells of one community usually contracted synchronously. By means of a bridge circuit, one microelectrode was used for simultaneously passing current and recording membrane potentials. The following chemical agents were electrophysiologically inactive at or below the concentrations indicated (in g/ml): acetylcholine (1.1 x 10–4), epinephrine (2 x 10–4), norepinephrine (3 x 10–4), and tetrodotoxin (1.3 x 10–5). In contrast, 2–7 mm Ba++ (used as a control) was very effective in partially depolarizing the cells, initiating spontaneity, and increasing the frequency of action potentials. Thus, cultured chick ventricular cells, both pacemaker and nonpacemaker, are insensitive to the autonomic agents. The data also suggest that acetylcholine is not necessarily involved in the electrogenesis of pacemaker potentials. The lack of effect of tetrodotoxin is unexplained.

By means of a pc bridge circuit one microelectrode was used for simultaneously passing current and recording transmembrane potentials. In some cells, depolarization increased the frequency of discharge whereas hyperpolarization decreased the frequency; the frequency/current relation was sigmoid. In other cells, polarizing currents were without effect upon frequency. The change in action potential magnitude was in proportion to the degree of polarization. From control values of about 5 mv/sec., the slope of the pacemaker potential increased to 60 mv/sec, upon depolarization and diminished to zero upon hyperpolarization. In many cells a transient hyperpolarization was produced on the cessation of depolarizing currents. The voltage/current relationship was linear and had a slope of about 13 MfL With an AC bridge circuit, the cell capacitance averaged 800 pf and the time constant, 9.6 msec. R,, was estimated to be 480 f~-cm ~ and C,,, 20 #f/cm ~. The magnitudes of some prepotentials were affected by polarizing currents, which suggests that the prepotentials represent postsynaptic potentials.It is now technically possible to record the transmembrane potentials of cultured heart cells (8, 11,22). For example, we have recorded mean resting potentials of 59 my and mean action potentials of 71 mv (22). Furthermore, the cells could be driven by intracellular or extracellular electrical stimulation with brief ( < 10 msec.) current pulses. The cultured myocardial cells are obviously similar in their electrophysiological properties to cells in intact hearts and hence represent a useful tool in the investigation of cell-to-cell interaction. An important advantage of the preparation is the relative simplicity with which one can interpret recorded potentials. The present study is concerned with the effect of current upon the transmembrane potentials of cultured chick heart cells.