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1 Pharmacology and Clinical Pharmacology Department of Basic Medical Sciences St. George's Hospital Medical School Cranmer Terrace London SW17 0RE, UK
Previously we have described the properties of store-operated channel currents (SOCs) in freshly dispersed rabbit portal vein smooth muscle cells. In addition to Ca2+ store depletion these SOCs could also be activated by 
-adrenoceptor stimulation and diacylglycerol (DAG) via a protein kinase C (PKC)-dependent mechanism. In the present study we have investigated the effect of ß-adrenoceptor stimulation on SOCs in rabbit portal vein myocytes. With whole-cell recording the selective ß-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 ß-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.
(Received 19 October 2004;
accepted after revision 2 November 2004;
first published online 4 November 2004)
Corresponding author AP Albert: Pharmacology and Clinical Pharmacology, Department of Basic Medical Sciences, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK. Email: aalbert{at}sghms.ac.uk
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