Angiotensin II stimulation of Ca²⁺-channel current in vascular smooth muscle cells is inhibited by lavendustin-A and LY-294002

Abstract

 Angiotensin II (AngII) is coupled to several important intracellular signaling pathways, and increases intracellular Ca²⁺. In vascular smooth muscle (VSM) cells, AngII is known to activate enzymes such as tyrosine protein kinase (Tyr-PK), phospholipase C (PLC), protein kinase C (PKC), and phophatidylinositol-3-kinase (PI-3-K). A non-receptor Tyr-PK, pp60^c-src, and PKC have been reported to stimulate the Ca²⁺ channels in VSM cells. However, less is known about AngII action on the voltage-gated Ca²⁺ channels. The Ca²⁺-channel currents of a cultured rat aortic smooth muscle cell line, A7r5, were recorded using whole-cell voltage clamp. Application of 50 nM AngII significantly increased the amplitude of Ba²⁺ currents through the voltage-gated Ca²⁺ channels (I _Ba) by 34.5±9.1% (n=10) within 1 min. In the presence of lavendustin-A (5 µM), a selective inhibitor of Tyr-PK, AngII failed to stimulate I _Ba (n=5). AngII stimulation of I _Ba was also prevented by (5 µM) LY-294002, an inhibitor of PI-3-K (n=5). In contrast, H-7 (30 µM), an inhibitor of PKC, did not prevent the effect of AngII on I _Ba (n=6). These results suggest that AngII may stimulate the Ca²⁺ channels of VSM cells through Tyr-PK and PI-3-K under conditions that probably exclude participation of PK-C.