THE EFFECTS OF SURAMIN ON PURINERGIC AND NORADRENERGIC NEUROTRANSMISSION IN THE RAT ISOLATED TAIL ARTERY

Intracellular microelectrode recording was used to examine the effects of suramin, a P-2-purinoceptor antagonist, on the electrical response s evoked by sympathetic nerve stimulation in the rat isolated tail art ery. Field stimulation (10 or 20 pulses at 0.5, 1 and 2 Hz) evoked a b iphasic electrical response, consisting of fast, transient excitatory junctional potentials (e.j.p.s) and a slow, prolonged depolarisation. Suramin (100 mu M) abolished the e.j.p.s and significantly increased t he amplitude of the slow depolarisation at all frequencies. In contras t, phentolamine (2 mu M) abolished the slow depolarisation, but had no effect on the magnitude of e.j.p.s. Neither drug altered the resting membrane potential of cells. The ability of suramin to inhibit e.j.p.s in rat tail artery is consistent with the proposal that it is a P-2X- purinoceptor antagonist and supports a role for ATP as an excitatory c otransmitter from the sympathetic nerves innervating this tissue. Sura min is also able to increase the alpha-adrenoceptor-mediated slow depo larisation by an unknown mechanism.