P. Viard et al., Involvement of both G protein alpha s and ss gamma subunits in ss-adrenergic stimulation of vascular L-type Ca2+ channels, BR J PHARM, 132(3), 2001, pp. 669-676
1 Previous data have shown that activation of beta (3)-adrenoceptors stimul
ates vascular L-type Ca2+ channels through a Gas-induced stimulation of the
cyclic AMP/PKA pathway. The present study investigated whether beta -adren
ergic stimulation also uses the G beta gamma /PI3K/PKC pathway to modulate
L-type Ca2+ channels in rat portal vein myocytes.
2 Peak Ba2+ current (I-Ba) measured using the whole-cell patch clamp method
was maximally increased by application of 10 muM isoprenaline after blocka
de of beta (3)-adrenoceptors by 1 muM SR59230A. Under these conditions, the
isoprenaline-induced stimulation of IBa was reversed by ICI-118551 (a spec
ific beta (2)-adrenoceptor antagonist) but not by atenolol (a specific beta
(1)-adrenoceptor antagonist). The beta (2)-adrenoceptor agonist salbutamol
increased IBa, an effect which was reversed by ICI-118551 whereas the beta
(1)-adrenoceptor agonist dobutamine had no effect on IBa
3 Application of PKA inhibitors (H-89 and Rp 8-Br-cyclic AMPs) or a PKC inh
ibitor (calphostin C) alone did not affect the beta (2)-adrenergic stimulat
ion of IBa whereas simultaneous application of both PKA and PKC inhibitors
completely blocked this stimulation.
4 The beta (2)-adrenergic stimulation of L-type Ca2+ channels was blocked b
y a pre-treatment with cholera toxin and by intracellular application of an
anti-Gas antibody (directed against the carboxyl terminus of Gas). In the
presence of H-89, intracellular infusion of an anti-G beta (com) antibody o
r a beta ARK(1) peptide as well as a pre-treatment with wortmannin (a PI3K
inhibitor) blocked the beta (2)-adrenergic stimulation of I-Ba
5 These results suggest that the beta (2)-adrenergic stimulation of vascula
r L-type Ca2+ channels involves both G alphas and G beta gamma subunits whi
ch exert their stimulatory effects through PKA and PI3K/PKC pathways, respe
ctively.