A G protein is involved in the angiotensin AT2 receptor inhibition of the T-type calcium current in non-differentiated NG108-15 cells

Abstract

In non-differentiated NG108-15 cells, both angiotensin II (Ang II) (100 nM) and CGP 42112 (100 nM) decreased the T-type calcium current amplitude by 24 ± 2% and 21 ± 3%, respectively. cGMP is not a mediator of the Ang II effect, since loading of cells with 50 μM cGMP did not prevent the inhibitory effects of Ang II. The effects of Ang II involves a non-identified GTPase activity since incubation with GDPβS (3 mM) completely reversed the inhibitory effect of Ang II while GTPγS mimicked its effect. However, Ang II binding was not affected by GTPγS, and the effect of Ang II was not modified in pertussis toxin-treated cells. The inhibitory effect of Ang II on the T- type Ca2+ current involves a phosphotyrosine phosphatase activity since sodium orthovanadate prevented the effects of Ang II, although microcystin- LR, a selective Ser/Thr phosphatase 1 and 2A inhibitor, did not modify the effect of Ang II. These results provide the first evidence of a modulation of membrane conductance by Ang II through the AT2 receptor and demonstrate the involvement of a phosphotyrosine phosphatase and a G protein in the AT2 transduction mechanism in NG108-15 cells. Moreover, our data suggest that phosphotyrosine phosphatase activation is proximal to receptor occupation, since sodium orthovanadate inhibits both GTPase activity and T-type current blockage induced by Ang II or CGP 42112, while GTPγS inhibition of the T- type calcium current is not impaired.