Functional coupling of human L-type Ca2+ channels and angiotensin AT1A receptors coexpressed in xenopus laevis oocytes: involvement of the carboxyl-terminal Ca2+ sensors.

A human recombinant L-type Ca2+ channel (alpha1C,77) was coexpressed with the rat angiotensin AT1A receptor in Xenopus laevis oocytes. In oocytes expressing only alpha1C,77 channels, application of human angiotensin II (1-10 microM) did not affect the amplitude or kinetics of Ba2+ currents (IBa). In sharp contrast, in oocytes coexpressing alpha1C,77 channels and AT1A receptors, application of 1 nM to 1 microM angiotensin gradually and reversibly inhibited IBa, without significantly changing its kinetics. The inhibitory effect of angiotensin on IBa was abolished in oocytes that had been preincubated with losartan (an AT1A receptor antagonist) or thapsigargin or injected with 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetate, pertussis toxin, guanosine-5'-O-(2-thio)diphosphate, or heparin, suggesting that the recombinant alpha1C channels were regulated by angiotensin through G protein-coupled AT1A receptors via activation of the inositol trisphosphate-dependent intracellular Ca2+ release pathway. Consistent with this hypothesis, no cross-signaling occurred between the AT1A receptor and a splice variant of alpha1C lacking Ca2+ sensors (alpha1C,86). The data suggest that the regulation of recombinant L-type Ca2+ channels by angiotensin is mediated by inositol trisphosphate-induced intracellular Ca2+ release and occurs at the molecular motif responsible for the Ca2+-induced inactivation of the channels.