title: Regulation of adenylyl cyclase type V/VI in smooth muscle: interplay of inhibitory G protein and Ca2+ influx.
abstract: The characteristics of inhibitory regulation of adenylyl cyclase V/VI by Ca2+ and G proteins were examined in dispersed gastric smooth muscle cells. The mechanisms were evoked separately, sequentially, or concurrently using ligand-gated and G protein-coupled receptor agonists and receptor-independent probes (e. g, thapsigargin). During the initial phase of agonist stimulation, alpha,beta-methylene-ATP, UTP, and ATP inhibited forskolin-stimulated cAMP formation in a concentration-dependent fashion. Inhibition by alpha,beta-methylene-ATP, which activates ligand-gated P2X receptors, was abolished by zero Ca2+, whereas inhibition by UTP, which activates P2Y2 receptors coupled to Gq/11 and Gi3, was not affected by zero Ca2+ but was abolished by pertussis toxin (PTX). Inhibition by ATP, which activates both P2X and P2Y2 receptors, was not affected by zero Ca2+ alone; but after inhibition mediated by Galphai3 was blocked with PTX, inhibition by Ca2+ influx was unmasked and was abolished by zero Ca2+. Inhibition by cholecystokinin-8 was observed only during the phase of capacitative Ca2+ influx and was blocked by zero Ca2+. Inhibition by UTP during this phase was not affected by zero Ca2+ alone; but after inhibition mediated by Galphai3 was blocked with PTX, inhibition by Ca2+ influx was unmasked and was abolished by zero Ca2+. Inhibition of adenylyl cyclase V/VI activity in smooth muscle can be mediated independently by inhibitory G proteins and Ca2+ influx but is exclusively mediated by inhibitory G proteins when both mechanisms are triggered.
authors.affiliation: Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298-0711, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Murthy
authors.forename: G M
authors.initials: GM
authors.lastname: Makhlouf
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D009130:Muscle, Smooth / Q000201:enzymology*; D011817:Rabbits; D013270:Stomach / Q000201:enzymology
chemical_list: D005576:Colforsin; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium