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.