Phosphoinositide 3-kinase γ mediates angiotensin II-induced stimulation of L-type calcium channels in vascular myocytes

Previous results have shown that in rat portal vein myocytes the beta gamma dimer of the G(13) protein transduces the angiotensin II-induced stimulation of calcium channels and increase in intracellular Ca2+ concentration through activation of phosphoinositide 3-kinase (PI3K). In the present work we determined which class I PI3K isoforms were involved in this regulation. Western blot analysis indicated that rat portal vein myocytes expressed only PI3K alpha and PI3K gamma and no other class I PI3K isoforms. In the intracellular presence of an anti-p110 gamma antibody infused by the patch clamp pipette, both angiotensin II- and G beta gamma -mediated stimulation of Ca2+ channel current were inhibited, whereas intracellular application of an anti-p110 alpha antibody had no effect. The anti-PI3K gamma antibody also inhibited the angiotensin II- and G beta gamma -induced production of phosphatidylinositol 3,4,5-trisphosphate. In Indo-1 loaded cells, the angiotensin II-induced increase in [Ca2+](i) was inhibited by intracellular application of the anti-PI3K gamma antibody, whereas the anti-PI3K alpha antibody had no effect. The specificity of the anti-PI3K gamma antibody used in functional experiments was ascertained by showing that this antibody did not recognize recombinant PI3K alpha in Western blot experiments. Moreover, anti-PI3K gamma antibody inhibited the stimulatory effect of intracellularly infused recombinant PI3K gamma on Ca2+ channel current without altering the effect of recombinant PI3K alpha. Our results show that, although both PI3K gamma and PI3K alpha are expressed in vascular myocytes, the angiotensin II-induced stimulation of vascular L-type calcium channel and increase of [Ca2+](i) involves only the PI3K gamma isoform.