Facilitation by P 2 receptor activation of acetylcholine release from rat motor nerve terminals: interaction with presynaptic nicotinic receptors

Abstract

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, β,γ-imido ATP on the nerve-evoked release of acetylcholine from adult rat hemidiaphragm preparations. β,γ-Imido ATP (10–100 μM) facilitated in a concentration-dependent manner evoked acetylcholine release, and 30 μM β,γ-imido ATP caused a 125% facilitation of evoked acetylcholine release. This facilitatory effect of β,γ-imido ATP (30 μM) was abolished by the P 2 receptor antagonists, suramin (100 μM) and pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS, 10 μM), 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 β,γ-imido ATP (30 μM) was also prevented by the nicotinic acetylcholine receptor antagonist, d-tubocurarine (1 μM) and the facilitatory effect (40%) of the nicotinic acetylcholine receptor agonist, 1,1-dimethyl-4-phenylpiperazinium (1 μM) was abolished by PPADS (10 μM). 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.