Intracellular angiotensin II stimulates voltage-operated Ca2+ channels in arterial myocytes

Although the presence of intracellular angiotensin II (Ang II) and of Ang II-binding sites has been reported, their roles in cell function have not been fully clarified. The purpose of the present study was to test the hypothesis that intracellular Ang II modifies voltage-operated Ca2+ channels in vascular smooth muscle. Ca2+ channel currents were recorded in guinea pig mesenteric arterial myocyteb with the whole-cell patch-clamp method. Intracellular dialysis of Ang II increased the amplitudes of Ca2+ channel current (133 +/- 9% of the control with 10 nmol/L Ang II, n=16). Concomitant dialysis of the Ang II type 1 receptor antagonist, CV-11974 (1 mumol/L, n= 11), but not the bath application of this drug, suppressed this Ang II action. In contrast, the dialysis of the Ang II type 2 receptor antagonist, PD123319 (1 mumol/L, n=5), failed to affect the Ang II action. Dialysis of either a phospholipase C inhibitor (U-73122, 10 mumol/L, n=5) or protein kinase C inhibitors (calphostin C, 100 nmol/L, n=5; protein kinase C inhibitor peptide-[19-36], 1 mumol/L, n=5) suppressed the Ang II action. Dialysis of KT5720 (100 nmol/L, n=5), an inhibitor of cAMP-dependent protein kinase, did not affect the Ang II action. Intracellular dialysis of angiotensin I (10 nmol/L) enhanced Ca2+ channel currents (13 3 +/- 8%, n=6). which were sensitive to intracellular enalaprilat (1 mumol/L, n=5) or CV-11974 (n=5). These results suggest that intracellular Ang II has a stimulating action on voltage-operated Ca2+ channels in vascular smooth muscle, possibly through intracellular binding sites similar to the Ang II type 1 receptor, which are associated with phospholipase C and protein kinase C.