title: A primary role for protein kinase A in smooth muscle relaxation induced by adrenergic agonists and neuropeptides.
abstract: Many studies suggest that smooth muscle relaxation caused by beta-adrenergic agents and various neuropeptides occurs as a result of an increase in cellular adenosine 3',5'-cyclic monophosphate (cAMP). However, the evidence is indirect, and furthermore does not demonstrate that an increase in cAMP is essential for mediating relaxation. To define more clearly the role of cAMP in receptor-mediated smooth muscle relaxation, we used a specific competitive antagonist of the action of cAMP on protein kinase A, (R)-p-adenosine 3',5'-cyclic phosphorothioate [(R)-p-cAMPS], and its S isomer, (S)-p-cAMPS, which functions as a cAMP agonist. In gastric smooth muscle cells from guinea pig, (S)-p-cAMPS caused a dose-related relaxation [50% inhibitory concentration (IC50) 86 +/- 59 nM]. Vasoactive intestinal peptide (VIP) produced smooth muscle cell relaxation (IC50 2.3 +/- 0.8 nM) through occupation of specific VIP receptors. (R)-p-cAMPS inhibited VIP-induced relaxation, with a rightward shift in the VIP dose-response curve, suggesting competitive antagonism. Furthermore, (R)-p-cAMPS inhibited relaxation induced by other agents that increase cellular cAMP (isoproterenol, calcitonin gene-related peptide, and glucagon) but not that induced by ATP or sodium nitroprusside. (R)-p-cAMPS had no effect on contraction stimulated by carbachol, cholecystokinin, or substance P. These data demonstrate that activation of protein kinase A is primarily responsible for mediating gastrin smooth muscle relaxation produced by adrenergic agents and various neuropeptides.
authors.affiliation: Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Z F
authors.initials: ZF
authors.lastname: Gu
authors.forename: R T
authors.initials: RT
authors.lastname: Jensen
authors.forename: P N
authors.initials: PN
authors.lastname: Maton
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009126:Muscle Relaxation / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009479:Neuropeptides / Q000494:pharmacology*; D011494:Protein Kinases / Q000502:physiology*; D013270:Stomach; D013566:Sympathomimetics / Q000494:pharmacology*; D013873:Thionucleotides / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
chemical_list: D009479:Neuropeptides; D013566:Sympathomimetics; D013873:Thionucleotides; C016957:adenosine-3',5'-cyclic phosphorothioate; D014660:Vasoactive Intestinal Peptide; D002217:Carbachol; D000242:Cyclic AMP; D011494:Protein Kinases