Choline acetyltransferase activity in heart: evidence for neuronal and not myocardial origin.

ROSKOSKI, ROBERT, JR., RUTH I. MCDONALD, LAURA M. ROSKOSKI, WILLIAM J. MARVIN, AND KENT HERMSMEYER. Choline acetyltransferase activity in heart: evidence for neuronal and not myocardial origin. Am. J. Physiol. 233(6): H642-H646, 1977 or Am. J. Physiol.: Heart Circ. Physiol. 2(6): H642-H646, 1977. -Choline acetyltransferase (EC 2.3.1.6) catalyzes the following reaction: acetyl coenzyme A + choline = 0-acetylcholine + coenzyme A. The enzyme is usually considered as a marker for cholinergic neurons; its presence in nonneuronal tissue is rigorously established for only the primate placenta. To determine whether myocardium per se or neurons are the source of heart choline acetyltransferase, preparations of isolated cardiac muscle cells were grown in cell culture and compared to embryonic heart for choline acetyltransferase and carnitine acetyltransferase (EC 2.3.1.7) activity. While the specific activity for the latter enzyme in the cultured heart cells was about 50% of that in freshly isolated chick embryo heart, choline acetyltransferase activity was undetectable (less than 1% of that in whole heart). Analysis of the cell fractions obtained by trypsinization revealed that choline acetyltransferase was associated with the unresolved sediment; the dispersed myocardial cells, however, lack both enzyme activity and apparent neuronal contamination. The possibility of a choline acetyltransferase inhibitor was ruled unlikely by combination of active extracts of embryonic heart and inactive cultured cells; the latter failed to alter the activity of the former. Parallel results were obtained from experiments with rat heart and rat heart cell cultures.