High sensitivity of cultured cardiac muscle cells to autonomic agents.

We have established conditions under which cultured embryonic myocardial cells are highly sensitive to the autonomic agents norepinephrine and acetylcholine and have determined that the most important factors affecting this sensitivity involve the application protocol. Using cells 3-5 days in culture, isolated from ventricles of 13-day chick embryos, the ED50 for noerpinephrine was 800 pM and that for acetylcholine was 370 pM. These cells were more than 2 orders of magnitude more sensitive than 13-day embryonic hearts freshly isolated, but not dispersed. Intracellular recording of the membrane actions of norepinephrine and acetylcholine on these cultured cells showed changes in pacemaker slope similar to those seen in freshly isolated hearts. These data demonstrate that preparation of ventricular muscle as isolated cells in culture does not necessarily result in the loss of sensitivity to autonomic agents. On the contrary, the isolated cells show the highest sensitivity to norepinephrine and acetylcholine that has been reported for the myocardium.