Cardiomyocyte-like cells differentiated in vitro from embryonic carcinoma cells P19 are characterized by functional expression of adrenoceptors and Ca²⁺ channels

P19 embryonal carcinoma cells were differentiated via embryolike aggregates (embryoid bodies) into spontaneously beating myocytes. During the whole process of differentiation the functional expression of cardiac-specific receptors and ionic channels was characterized by measuring the chronotropic reactivity, action potentials, and ionic currents in response to various cardioactive drugs. Positive chronotropic effects obtained at different maximal effective concentrations of adrenoceptor-mediated agonists indicated differential adrenoceptor expression during the in vitro development of cardiomyocyte-like cells. No cardiac-specific response was obtained with the muscarinic cholinoceptor agonist carbachol. Single beating cells were enzymatically isolated and investigated by the patch-clamp technique. Pacemaker action potentials similar to those of embryonal cardiomyocytes exhibited amplitudes ranging from 50 to 85 mV. The action potentials were synchronous to the mechanical contractions and, comparable to the chronotropic effects, were modulated by BayK 8644, isradipine, and adrenaline. The functional expression of L-type Ca²⁺ channels was demonstrated by the Ca²⁺ channel blockers isradipine, nisoldipine, gallopamil, and diltiazem causing negative chronotropic responses, as well as by the Ca²⁺ channel activator BayK 8644 causing positive chronotropic responses. These effects gradually increased with time of differentiation. The expression of L-type Ca²⁺ channels and of nicotinic acetylcholine receptors was confirmed in voltage-clamp experiments. The study demonstrates that P19 embryonal carcinoma cells can be induced to differentiate into cardiomyocyte-like cells comparable to embryonal and neonatal heart cells lacking the muscarinic cholinoceptor response only.