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KMID : 0811719990030020165
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Korean Journal of Physiology & Pharmacology
1999 Volume.3 No. 2 p.165 ~ p.174
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Evidence for Adenosine Triphosphate (ATP) as an Excitatory Neuro-transmitter in Guinea-Pig Gastric Antrum
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Tong Mook Kang
Wenxie Xu/Sung Joon Kim/Seung Cheol Ahn 2Young Chul Kim/Insuk So/Myoung Kyu Park/Dae-Yong Uhm
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Abstract
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We explore the question of whether adenosine 5'-triphosphate (ATP) acts as an excitatory neurotransmitter in guinea-pig gastric smooth muscle. In an organ bath system, isometric force of the circular smooth muscle of guinea-pig gastric antrum was measured in the presence of atropine and guanethidine. Under electrical field stimulation (EFS) at high frequencies (＞20 Hz), NO-mediated relaxation during EFS was followed by a strong contraction after the cessation of EFS (a 'rebound-contraction'). Exogenous ATP mimicked the rebound-contraction. A known P2Y?purinoceptor antagonist, reactive blue 2 (RB-2), blocked the rebound-contraction while selective desensitization of P2Y?purinoceptor with α,β?MeATP did not affect it. ATP and 2-MeSATP induced smooth muscle contraction, which was effectively blocked by RB-2 and suramin, a nonselective P2?purinoceptor antagonist. Particularly, in the presence of RB-2, exogenous ATP and 2-MeSATP inhibited spontaneous phasic contractions, suggesting the existence of different populations of purinoceptors. Both the rebound-contraction and the agonist-induced contraction were not inhibited by indomethacin. The rank orders of agonists' potency were 2-MeSATP > ATP ge UTP for contraction and α,β?MeATP≥β,γ?MeATP for inhibition of the phasic contraction, that accord with the commonly accepted rank order of the classical P2Y?purinoceptor subtypes. Electrical activities of smooth muscles were only slightly influenced by ATP and 2-MeSATP, whereas α,β?MeATP attenuated slow waves with membrane hyperpolarization. From the above results, it is suggested that ATP acts as an excitatory neurotransmitter, which mediates the rebound-contraction via P2Y?purinoceptor in guinea-pig gastric antrum.
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KEYWORD
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ATP, Smooth musle, Purinoceptors, Stomach,
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