Beta-3 adrenergic stimulation of L-type Ca2+ channels in rat portal vein myocytes

1 The effects of beta(3)-adrenergic stimulation were studied on the L-type Ca2+ channel in single myocytes from rat portal vein using the whole-cell m ode of the patch-clamp technique. 2 Reverse transcription-polymerase chain reaction showed that beta(1)-, bet a(2)- and beta(3)-adrenoceptor subtypes were expressed in rat portal Vein m yocytes. Application of both propranolol (a nonselective beta(1)- and beta( 2)-adrenoceptor antagonist) and SR59230A (a beta(3)-adrenoceptor antagonist ) were needed to inhibit the isoprenaline-induced increase in L-type Ca2+ c hannel current. 3 L-type Ca2+ channels were stimulated by CGP12177A (a beta(3)-adrenoceptor agonist with potent beta(1)-and beta(2)-adrenoceptor antagonist property) in a manner similar to that of isoprenaline. The CGP12177A-induced stimulat ion of Ca2+ channel current was blocked by SR59230A, cyclic AMP-dependent p rotein kinase inhibitors, H-89 and Rp 8-Br-cyclic AMPs, but was unaffected by protein kinase C inhibitors, GF109203X and 19-31 peptide. This stimulati on was mimicked by forskolin and 8-Br-cyclic AMP. In the presence of okadai c acid (a phosphatase inhibitor), the beta(3)-adrenoceptor-induced stimulat ion was maintained after withdrawal of the agonist. 4 The beta(3)-adrenoceptor stimulation of L-type Ca2+ channels was blocked by a pretreatment with cholera toxin and by the intracellular application o f an anti-G alpha(s) antibody. This stimulation was unaffected by intracell ular infusion of an anti-G beta(com) antibody and a beta ARK(1) peptide. 5 These results show that activation of beta(3)-adrenoceptors stimulates L- type Ca2+ channels in vascular myocytes through a G alpha(s)-induced stimul ation of the cyclic AMP/protein kinase A pathway and the subsequent phospho rylation of the channels.