Retention of fully differentiated electrophysiological properties of chick embryonic heart cells in culture.

Many cultured cells in spherical reaggregates (100–1000 μm diameter), prepared using cells isolated from embryonic chick ventricles (16 days in ovo), retain great sensitivity to tetrodotoxin (TTX; 0.1 μg/ml), rapidly rising action potentials (up to 200 V/sec), high resting potentials (up to ?90 mV), and they lack automaticity. The Na⁺ channels generating the action potential upstroke inactivate totally at about ?50 mV. The chronaxie (hence, excitability), the ratio of $\text{P}{}_{\mathrm{<mtext>Na</mtext>}}\text{P}{}_{\mathrm{<mtext>K</mtext>}}$, and the intracellular K⁺ concentration are about the same as in adult cells. Following blockade of the Na⁺ channels with TTX, norepinephrine produces slowly rising overshooting responses, indicating the presence of functional beta-adrenergic receptors. Thus, trypsin-dispersed myocardial cells can be made to retain highly differentiated membrane properties in vitro.