Facilitation by P2 receptor activation of acetylcholine release from rat motor nerve terminals:: interaction with presynaptic nicotinic receptors

ATP is released from motor nerve endings together with acetylcholine. Released adenine nucleotides can be extracellularly metabolized into adenosine, which is a presynaptic neuromodulator at neuromuscular junctions, but it is not known if P-2 receptor activation also modulates acetylcholine release from mature motor nerve endings. We now tested the effect of a stable ATP analogue, beta,gamma-imido ATP on the nerve-evoked release of acetylcholine from adult rat hemidiaphragm preparations. beta,gamma-Imido ATP (10-100 mu M) facilitated in a concentration-dependent manner evoked acetylcholine release, and 30 mu M beta,gamma-imido ATP caused a 125% facilitation of evoked acetylcholine release. This facilitatory effect of beta,gamma-imido ATP (30 mu M) was abolished by the P-2 receptor antagonists, suramin (100 mu M) and pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, 10 mu M), but not by the A(1) or A(2A) adenosine receptor antagonists, 1,3-dipropyl-8-cyclopentylxanthine (50 nM) and ZM 241385 (50 nM), respectively. The facilitation of acetylcholine release by beta,gamma-imido ATP (30 mu M) was also prevented by the nicotinic acetylcholine receptor antagonist, D-tubocurarine (1 mu M) and the facilitatory effect (40%) of the nicotinic acetylcholine receptor agonist, 1,1-dimethyl-4-phenyIpiperazinium (1 mu M) was abolished by PPADS (10 mu M). These results demonstrate a presynaptic facilitatory effect of P-2 receptor activation at the rat phrenic nerve endings, which is tightly coupled with the presynaptic nicotinic autofacilitatory system. (C) 2000 Elsevier Science B.V. Ail rights reserved.