P2X purinoceptors mediate an endothelium-dependent hyperpolarization in longitudinal smooth muscle of anterior mesenteric artery in young chickens.
OBJECTIVE
The chicken anterior mesenteric artery contains an outer longitudinal smooth muscle layer, whose neural regulation remains to be elucidated. ATP evokes a depolarization in the smooth muscle through P2Y purinoceptors. However, there may be an additional inhibitory regulation because blockade of P2Y purinoceptors converts the depolarization to hyperpolarization. The objective of the present study was to examine the mechanism underlying this hyperpolarization.


METHODS
Membrane potentials of longitudinal smooth muscle of the chicken mesenteric artery were recorded with a microelectrode technique. Perivascular nerves were stimulated by applying electrical field stimulation (EFS).


RESULTS
EFS induced a hyperpolarization in preparations obtained from 5-week-old chickens, whereas it evoked a depolarization in those from 12-week-old chickens. The EFS-evoked hyperpolarization in 5-week-old chickens was blocked by a non-specific purinoceptor antagonist, suramin, and by a specific P2X purinoceptor antagonist, pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid. Desensitization of the P2X purinoceptor with its agonist alpha,beta-MeATP significantly suppressed EFS-evoked hyperpolarization. Blockade of the P2Y purinoceptor did not affect EFS-evoked hyperpolarization. The application of the NOS inhibitor Nomega-nitro-L-arginine methyl ester or the removal of the endothelium inhibited the hyperpolarization. The application of the nitric oxide (NO) donor sodium nitroprusside mimicked the hyperpolarization. Reverse transcriptase-PCR showed that P2X purinoceptors are expressed in the endothelium of the anterior mesenteric artery.


CONCLUSIONS
Hyperpolarization in the longitudinal smooth muscle of the chicken anterior mesenteric artery was induced by ATP. ATP released from perivascular nerves may act on P2X purinoceptors in the endothelium and thereby stimulate NO production.
Alkayed
F
F
Department of Basic Veterinary Science, The United Graduate School of Veterinary Sciences, Gifu University, Gifu, Japan.
Boudaka
A
A
Shiina
T
T
Takewaki
T
T
Shimizu
Y
Y
D000375:Aging / Q000502:physiology; D000818:Animals; D002645:Chickens; D004558:Electric Stimulation; D004730:Endothelium, Vascular / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008638:Mesenteric Arteries / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D020033:Protein Isoforms / Q000096:biosynthesis; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis / Q000502:physiology*
D020030:Nitric Oxide Donors; D020033:Protein Isoforms; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase
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