Distinct Functions of Gq and G11 Proteins in Coupling α1-Adrenoreceptors to Ca2+ Release and Ca2+ Entry in Rat Portal Vein Myocytes

doi:10.1074/jbc.272.8.5261

Distinct Functions of G_q and G₁₁ Proteins in Coupling α₁-Adrenoreceptors to Ca²⁺ Release and Ca²⁺ Entry in Rat Portal Vein Myocytes*

^‡ Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, CNRS ESA 5017, Université de Bordeaux II, 146 rue Léo Saignat, 33076 Bordeaux Cedex, France and
^¶ Institut für Pharmakologie, Freie Universität Berlin, Thielallee 69/71, D-14195 Berlin, Federal Republic of Germany

^∥ To whom correspondence should be addressed:
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, CNRS ESA 5017, Faculté de Pharmacie, Université de Bordeaux II, 146 rue Léo Saignat, 33076 Bordeaux, France.
Tel.: 33-5-57-57-12-31; Fax: 33-5-57-57-12-26.

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 intracellular stores. Gα₁₁ may enhance the Ca²⁺-activated Ca²⁺ influx that replenishes intracellular Ca²⁺ stores.

Footnotes

↵^§ Supported by a fellowship from the Fondation pour la Recherche Medicale (France).
↵* This work was supported by grants from Centre National de la Recherche Scientifique (France) and from the Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie (Germany). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

[Ca²⁺]_i

cytoplasmic Ca²⁺ concentration

PBS

phosphate-buffered saline solution

nt

nucleotide(s)

βARK

β-adrenergic receptor kinase.
↵² N. Macrez-Leprêtre, F. Kalkbrenner, J. L. Morel, G. Schultz, and J. Mironneau, manuscript in preparation.
- Received October 22, 1996.