1 The object of the present study was to clarify the neurotransmitter(s) controlling membrane responses to electrical field stimulation (EFS) in the circular smooth muscle cells of first-order branches of chicken anterior mesenteric artery.
2 EFS (five pulses at 20 Hz, 1 ms) evoked a hyperpolarization of amplitude
21.671.2 mV, total duration 21.871.2 s and latency 641.7781.9 ms. The response was tetrodotoxin-sensitive and nonadrenergic noncholinergic (NANC) in nature.
3 The NANC response was blocked by the nonspecific purinergic antagonist, suramin, indicating that the response is mediated by the neurotransmitter adenosine 50-triphosphate (ATP).
4 Either desensitization or blockade of P2Y receptor with its putative agonist 2-methylthioATP (1 mM for 30 min) or with its antagonist cibacron blue F3GA (10 mM), respectively, abolished the purinergic hyperpolarization. PPADS at concentrations up to 100 mM had no effect on the EFSinduced response, indicating that this response is mediated through P2Y, but not P2X, receptor.
In addition, the response was completely abolished by two specific P2Y1 receptor antagonists, namely, MRS 2179 (300 nM) and A3P5PS (10 mM).
5 Removal of the endothelium abolished the purinergic hyperpolarization, which was converted, in some preparations, to a small depolarization, indicating that the hyperpolarizing response is endothelium-dependent.
6 The present study suggests that in first-order branches of chicken anterior mesenteric artery, ATP released from perivascular nerves may diffuse to the endothelium-activating P2Y1 receptor to induce release of an inhibitory substance that mediates hyperpolarization in the circular smooth muscle.