EXOCYTOSIS FROM A SINGLE-RAT CHROMAFFIN CELL BY CHOLINERGIC AND PEPTIDERGIC NEUROTRANSMITTERS

Secretion of catecholamines from chromaffin cells is mediated by cholinergic and peptidergic neurotransmitters.(3,11,14) The cholinergic transmitter acetylcholine activates both nicotinic and muscarinic receptors to trigger catecholamine secretion in rat adrenal medulla.(17) Vasoactive intestinal polypeptide (VIP) has been identified as the peptidergic transmitter in rat adrenal medulla and may also be the non-cholinergic transmitter in bovine adrenal.(18,23) Pituitary adenylate cyclase activating polypeptide (PACAP), a VIP-like secretin peptide, is also found in the adrenal,(5) and is a potent secretagogue.(7,21) Thus, PACAP may be another peptidergic transmitter at the adrenal synapse.(19) A most intriguing property of rat chromaffin cells is that stimulation of nicotinic, muscarinic, VIP or PACAP receptors are each able to produce robust catecholamine secretion on their own.(11-13,21) This raises the question of whether a single chromaffin cell can respond to each of the above agonists or whether the secretion is due to subpopulations of chromaffin cells. This issue was addressed by using electrochemical techniques to monitor exocytosis from individual chromaffin cells in culture.(2,9,22) We demonstrate that acetylcholine, nicotine, muscarine, VIP and PACAP are each able to evoke catecholamine secretion from a single chromaffin cell. Some cells only responded to acetylcholine. Furthermore, each agonist produced a distinct pattern of exocytosis. Muscarine-evoked secretion exhibited a latency of 0.5-2 s, but exocytosis persisted up to 30 s following 500 ms stimulation. Nicotine produced an immediate response which usually ended within 10 s. The secretory pattern following acetylcholine appeared to be the sum of the nicotinic and muscarinic patterns, showing both rapid onset and longer duration. The unique property of peptidergic stimulation was that a brief exposure caused exocytosis to persist for up to 2 min. Like muscarine, peptides exhibited latency in producing exocytosis. These findings support the idea that the interactive control of catecholamine secretion by nicotinic, muscarinic and peptidergic receptors occurs at the level of single cells.