An electrophysiological study of excitatory purinergic neuromuscular transmission in longitudinal smooth muscle of chicken anterior mesenteric artery

1 The object of the present study was to clarify the neurotransmitters controlling membrane responses to electrical field stimulation (EFS) in the longitudinal smooth muscle cells of the chicken anterior mesenteric artery. 2 EFS (5 pulses at 20 Hz) evoked a depolarization of amplitude 19.7+/-2.1 mV, total duration 29.6+/-3.1 s and latency 413.0+/-67.8 ms. This depolarization was tetrodotoxin (TTX)-sensitive and its amplitude was partially decreased by atropine (0.5 mu M); however, its duration was shortened by further addition of prazosin (10 mu M). 3 Atropine/prazosin-resistant component was blocked by the nonspecific purinergic antagonist, suramin, in a dose-dependent manner, indicating that this component is mediated by the neurotransmitter adenosine 50-triphosphate (ATP). 4 Neither desensitization nor blocking of P2X receptor with its putative receptor agonist alpha,beta-methylene ATP (alpha,beta-MeATP, 1 mu M) and its antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic (PPADS, up to 50 mM), had significant effect on the purinergic depolarization. In contrast, either desensitization or blocking of P2Y receptor with its putative agonist 2-methylthioATP (2-MeSATP, 1 mu M) and its antagonist Cibacron blue F3GA (CBF3GA, 10 mu M) abolished the purinergic depolarization, indicating that this response is mediated through P2Y but not P2X receptor. 5 The purinergic depolarization was inhibited by pertussis toxin (PTX, 600 ng ml(-1)). Furthermore, it was significantly inhibited by a phospholipase C (PLC) inhibitor, U-73122 (10 mu M), indicating that the receptors involved in mediating the purinergic depolarization are linked to a PTX-sensitive G-protein, which is involved in a PLC-mediated signaling pathway. 6 Data of the present study suggest that the EFS-induced excitatory membrane response occurring in the longitudinal smooth muscle of the chicken anterior mesenteric artery is mainly purinergic in nature and is mediated via P2Y purinoceptors.