Beta‐3 adrenergic stimulation of L‐Type Ca2+ channels in rat portal vein myocytes

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Abstract
The effects of β3‐adrenergic stimulation were studied on the L‐type Ca2+ channel in single myocytes from rat portal vein using the whole‐cell mode of the patch‐clamp technique. Reverse transcription‐polymerase chain reaction showed that β1‐, β2‐ and β3‐adrenoceptor subtypes were expressed in rat portal vein myocytes. Application of both propranolol (a non‐selective β1‐ and β2‐adrenoceptor antagonist) and SR59230A (a β3‐adrenoceptor antagonist) were needed to inhibit the isoprenaline‐induced increase in L‐type Ca2+ channel current. L‐type Ca2+ channels were stimulated by CGP12177A (a β3‐adrenoceptor agonist with potent β1‐ and β2‐adrenoceptor antagonist property) in a manner similar to that of isoprenaline. The CGP12177A‐induced stimulation of Ca2+ channel current was blocked by SR59230A, cyclic AMP‐dependent protein kinase inhibitors, H‐89 and Rp 8‐Br‐cyclic AMPs, but was unaffected by protein kinase C inhibitors, GF109203X and 19‐31 peptide. This stimulation was mimicked by forskolin and 8‐Br‐cyclic AMP. In the presence of okadaic acid (a phosphatase inhibitor), the β3‐adrenoceptor‐induced stimulation was maintained after withdrawal of the agonist. The β3‐adrenoceptor stimulation of L‐type Ca2+ channels was blocked by a pretreatment with cholera toxin and by the intracellular application of an anti‐Gαs antibody. This stimulation was unaffected by intracellular infusion of an anti‐Gβcom antibody and a βARK1 peptide. These results show that activation of β3‐adrenoceptors stimulates L‐type Ca2+ channels in vascular myocytes through a Gαs‐induced stimulation of the cyclic AMP/protein kinase A pathway and the subsequent phosphorylation of the channels. British Journal of Pharmacology (2000) 129, 1497–1505; doi:10.1038/sj.bjp.0703187