Distinct functions of G(q) and G(11) proteins in coupling alpha(1)-adrenoreceptors to Ca2+ release and Ca2+ entry in rat portal vein myocytes

In this study, we identified the subunit composition of G(q) and G(11) proteins coupling alpha(1)-adrenoreceptors to increase in cytoplasmic Ca2+ concentration ([Ca2+](i)) in rat portal vein myocytes maintained in short-term primary culture, We used intranuclear antisense oligonucleotide injection to inhibit selectively the expression of subunits of G protein. Increases in [Ca2+](i) were measured in response to activation of alpha(1)-adrenoreceptors, angiotensin AT(1) receptors, and caffeine. Antisense oligonucleotides directed against the mRNAs coding for alpha(q), alpha(11), beta(1), beta(3), gamma(2), and gamma(3) subunits selectively inhibited the increase in [Ca2+](i) activated by alpha(1)-adrenoreceptors. A corresponding reduction of the expression of these G protein subunits was immunochemically confirmed. In experiments performed in Ca2+-free solution only cells injected with anti-alpha(q) antisense oligonucleotides displayed a reduction of the alpha(1)-adrenoreceptor-induced Ca2+ release, In contrast, in Ca2+-containing solution, injection of anti-alpha(11) antisense oligonucleotides suppressed the alpha(1)-adrenoreceptor-induced stimulation of the store-operated Ca2+ influx, Agents that specifically bound G beta gamma subunits (anti-beta(com) antibody and overexpression of a beta-adrenergic receptor kinase carboxyl-terminal fragment) had no effect on the alpha(1)-adrenoreceptor induced signal transduction, Taken together, these results suggest that alpha(1)-adrenoreceptors utilize two different G alpha subunits to increase [Ca2+](i). G alpha(q) may activate phosphatidylinositol 4,5-bisphosphate hydrolysis and induce release of Ca2+ from intracellular stores, G alpha(11) may enhance the Ca2+-activated Ca2+ influx that replenishes intracellular Ca2+ stores.