G protein heterotrimer Gα13β1γ3 couples the angiotensin AT(1A) receptor to increases in cytoplasmic Ca2+ in rat portal vein myocytes

Abstract

The subunit composition of angiotensin AT1 receptor-activated G protein was identified by using antisense oligonucleotide injection into the nucleus of rat portal vein myocytes. In these cells, we have previously shown that increases in the cytoplasmic calcium concentration ([Ca2+](i)) induced by activation of angiotensin AT1 receptors were dependent on extracellular Ca2+ entry by L-type Ca2+ channels and subsequent Ca2+-induced Ca2+ release from the intracellular stores. The angiotensin AT1 receptor- activated increases in [Ca2+](i) were selectively inhibited by injection of antisense oligonucleotides directed against the mRNas coding for the α13, β1, and γ3 subunits. A correlating reduction in Gα13, Gβ1, and Gγ3 protein expression was confirmed by immunocytochemistry. In addition, anti- α13 antibody and synthetic peptide corresponding to the carboxyl terminus of the Gα13 subunit inhibited, in a concentration-dependent manner, the angiotensin AT1 receptor-mediated Ca2+ response. Reverse transcription- polymerase chain reaction analysis showed that only the angiotensin AT(1A) receptor was expressed in rat portal vein smooth muscle. Furthermore, injection of anti-AT(1A) oligonucleotides selectively inhibited the angiotensin II-induced increase in [Ca2+](i). We conclude that the receptor-activated signal leading to increases in [Ca2+](i) is transduced by the heterotrimeric G13 protein composed of α13/β1/γ3 subunits and that the carboxyl terminus of the Gα13 subunit interacts with the angiotensin AT(1A) receptor.