Acetylcholine-induced potential fluctuations and underlying currents in rat adrenal chromaffin cells

Adrenal chromaffin cells are innervated by splanchnic nerves. The neurotransmitter acetylcholine (ACh), released at the terminal, somehow triggers the catecholamine secretion. On ACh stimulation the chromaffin cell in culture depolarizes with prominent potential fluctuations and generates repetitive action potentials. Because these cells are small (10-16 micron in diameter) and have a large input resistance (about 6 G omega), the stochastic nature of channel opening and closing can generate considerable voltage noises that underlie the repetitive generation of action potentials. The action potential in the adrenal chromaffin cell is mediated by Na as well as Ca inward currents. Thus, Ca2+ entering the cell during the action potential may link the ACh stimulation and the hormone secretion. In addition, Ca2+ entering the cell through ACh receptor channels may also significantly contribute to secretion. It is most likely, however, that ACh receptors are highly localized at the subsynaptic area, which is only a small portion of the cell surface. Ca influx through ACh receptor channels is thus limited to the area close to the synapse, whereas voltage-dependent Ca channels may provide Ca2+ through the entire surface. Ca channels probably play an important role in stimulus-secretion coupling in the adrenal chromaffin cell.