Insensitivity of cultured chick heart cells to autonomic agents and tetrodotoxin

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.