Facilitation by P-2 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. Relea sed 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 a nalogue, 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 rel ease, and 30 mu M beta,gamma-imido ATP caused a 125% facilitation of evoked acetylcholine release. This facilitatory effect of beta,gamma-imido ATP (3 0 mu M) was abolished by the P-2 receptor antagonists, suramin (100 mu M) a nd 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 facil itation of acetylcholine release by beta,gamma-imido ATP (30 mu M) was also prevented by the nicotinic acetylcholine receptor antagonist, D-tubocurari ne (1 mu M) and the facilitatory effect (40%) of the nicotinic acetylcholin e receptor agonist, 1,1-dimethyl-4-phenyIpiperazinium (1 mu M) was abolishe d by PPADS (10 mu M). These results demonstrate a presynaptic facilitatory effect of P-2 receptor activation at the rat phrenic nerve endings, which i s tightly coupled with the presynaptic nicotinic autofacilitatory system. ( C) 2000 Elsevier Science B.V. Ail rights reserved.