Distinct functions of G(q) and G11 proteins in coupling α1- adrenoreceptors to Ca2+ release and Ca2+ entry in rat portal vein myocytes

Abstract

In this study, we identified the subunit composition of G(q) and G11 proteins coupling α1-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 α1- adrenoreceptors, angiotensin AT1 receptors, and caffeine. Antisense oligonucleotides directed against the mRNAs coding for α(q), α11, β1, β3, γ2, and γ3 subunits selectively inhibited the increase in [Ca2+](i) activated by α1-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- α(q) antisense oligonucleotides displayed a reduction of the α1- adrenoreceptor-induced Ca2+ release. In contrast, in Ca2+-containing solution, injection of anti-α11 antisense oligonucleotides suppressed the α1-adrenoreceptor-induced stimulation of the store-operated Ca2+ influx. Agents that specifically bound Gβγ subunits (anti-β(com) antibody and overexpression of a β-adrenergic receptor kinase carboxyl-terminal fragment) had no effect on the α1-adrenoreceptor-induced signal transduction. Taken together, these results suggest that α1-adrenoreceptors utilize two different Gα subunits to increase [Ca2+](i). Gα(q) may activate phosphatidylinositol 4,5-bisphosphate hydrolysis and induce release of Ca2+ from intraeellular stores. Gα11 may enhance the Ca2+-activated Ca2+ influx that replenishes intracellular Ca2+ stores.