title: Stimulation of beta-adrenoceptors inhibits store-operated channel currents via a cAMP-dependent protein kinase mechanism in rabbit portal vein myocytes.
abstract: Previously we have described the properties of store-operated channel currents (SOCs) in freshly dispersed rabbit portal vein smooth muscle cells. In addition to Ca(2+) store depletion these SOCs could also be activated by alpha-adrenoceptor stimulation and diacylglycerol (DAG) via a protein kinase C (PKC)-dependent mechanism. In the present study we have investigated the effect of beta-adrenoceptor stimulation on SOCs in rabbit portal vein myocytes. With whole-cell recording the selective beta-adrenoceptor agonist isoprenaline reduced the current evoked by cyclopiazonic acid (CPA, sarcoplasmic/endoplasmic reticulum ATPase inhibitor) by over 85%. With cell-attached patch recording, bath application of isoprenaline produced a pronounced inhibition of SOC activity evoked by either CPA or the acetoxymethyl ester form of BAPTA (BAPTA-AM). SOC activity evoked by CPA, the DAG analogue, 1-oleoyl-acetyl-sn-glycerol (OAG) or the phorbol ester, phorbol-12,13-dibutyrate (PDBu) was also markedly inhibited by the adenylate cyclase activator, forskolin, and the cell-permeable non-hydrolysable analogue of cyclic adenosine monophosphate (cAMP), 8-Br-cAMP. With inside-out patches, bath application of PDBu evoked channel currents with similar properties to SOCs which were inhibited by over 90% by a catalytic subunit of protein kinase A (PKA) and by 8-Br-cAMP. Moreover bath application of PKA inhibitors, H-89, KT5720 and an inhibitory peptide to quiescent cell-attached or inside-out patches, activated channel currents with similar properties to SOCs. These data suggest that in rabbit portal vein myocytes, stimulation of beta-adrenoceptors inhibits SOC activity via a cAMP-dependent protein kinase signal transduction cascade. In addition it is concluded that constitutive PKA activity has a profound inhibitory effect on SOC activity in this vascular preparation.
authors.affiliation: Pharmacology and Clinical Pharmacology, Department of Basic Medical Sciences, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK.
authors.forename: M
authors.initials: M
authors.lastname: Liu
authors.forename: W A
authors.initials: WA
authors.lastname: Large
authors.forename: A P
authors.initials: AP
authors.lastname: Albert
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002469:Cell Separation; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000037:antagonists & inhibitors*; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000201:enzymology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010766:Phosphorylation; D011169:Portal Vein / Q000378:metabolism*; D011817:Rabbits; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D012996:Solutions
chemical_list: D000318:Adrenergic beta-Agonists; D007473:Ion Channels; D043562:Receptors, G-Protein-Coupled; D012996:Solutions; D015124:8-Bromo Cyclic Adenosine Monophosphate; D015240:Phorbol 12,13-Dibutyrate; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol