• Journal of Life Science
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• v.8 no.4
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• pp.395-399
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• 1998

Neurokinin A(NKA) and its derivatives ([Nle$^{7}$NKA,[Leu$^{7}$NKA] were synthesized by solid phase peptide synthesis method using Fmoc-TFA strategy and their smooth muscle contractile activities were measured to examine the structural effect of alkyl group at the 7th amino acid NKA on the smooth muscle contractile activity. The smooth muscle contractile activity. The smooth muscle contractile activities of [Nle$^{7}$]NKA and [Leu$^{7}$]NKA were only 5.64% and 1.55%, respectively when compared with NKA. This result suggested that the more three dimensional structure of th 7th amino acid as well as the whole message segment of NKA would be necessary to show the biological activity.

• The Korean Journal of Physiology and Pharmacology
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• v.3 no.2
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• pp.165-174
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• 1999

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 $P_{2Y}-purinoceptor$ antagonist, reactive blue 2 (RB-2), blocked the rebound-contraction while selective desensitization of $P_{2Y}-purinoceptor$ with ${\alpha},{\beta}-MeATP$ did not affect it. ATP and 2-MeSATP induced smooth muscle contraction, which was effectively blocked by RB-2 and suramin, a nonselective $P_2-purinoceptor$ 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 ${\alpha},{\beta}-MeATP\;{\ge}\;{\beta},{\gamma}-MeATP$ for inhibition of the phasic contraction, that accord with the commonly accepted rank order of the classical $P_{2Y}-purinoceptor$ subtypes. Electrical activities of smooth muscles were only slightly influenced by ATP and 2-MeSATP, whereas ${\alpha},{\beta}-MeATP$ 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 $P_{2Y}-purinoceptor$ in guinea-pig gastric antrum.