Electrophysiology of autonomic neuromuscular transmission involving ATP

Electrophysiological investigations of autonomic neuromuscular transmission have provided great insights into the role of ATP as a neurotransmitter. B urnstock and Holman made the first recordings of excitatory junction potent ials (e.j.p.s) produced by sympathetic nerves innervating the smooth muscle of the guinea-pig vas deferens. This led to the identification of ATP as t he mediator of e.j.p.s in this tissue, where ATP acts as a cotransmitter wi th noradrenaline. The e.j.p.s are mediated solely by ATP acting on P2X(1) r eceptors lending to action potentials and a rapid phasic contraction, whils t noradrenaline mediates a slower, tonic contraction which is not dependent on membrane depolarisation. Subsequent electrophysiological studies of the autonomic innervation of smooth muscles of the urogenital, gastrointestina l and cardiovascular systems have revealed a similar pattern of response, w here ATP mediates a fast electrical and mechanical response, whilst another transmitter such as noradrenaline, acetylcholine, nitric oxide or a peptid e mediates a slower response. The modulation of junction potentials by a va riety of pre-junctional receptors and the mechanism of inactivation of ATP as a neurotransmitter will also be described. (C) 2000 Elsevier Science B.V . All rights reserved.