Tyrosine kinase is involved in angiotensin II-stimulated phospholipase D activation in aortic smooth muscle cells: Function of Ca²⁺ influx

In the present study, we examined the effect of angiotensin II (Ang II) on phosphatidylcholine-hydrolyzing phospholipase D activity in subcultured rat aortic smooth muscle cells (SMC). Ang II dose-dependently stimulated the formation of choline and inositol phosphates. The effect of Ang II on the formation of inositol phosphates (EC₅₀ was 0.249 ± 0.091 nM) was more potent than that on the formation of choline (EC₅₀ was 2.39 ± 1.29 nM). A combination of Ang II and 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, additively stimulated the formation of choline. Staurosporine, an inhibitor of protein kinases, inhibited the TPA-induced formation of choline, but had little effect on the Ang II-induced choline formation. Ang II stimulated Ca²⁺ influx from extracellular space time- and dose-dependently. The depletion of extracellular Ca²⁺ by (ethylenebis(oxyethylenenitrilo))tetraacetic acid (EGTA) significantly reduced the Ang II-induced formation of choline. Genistein and tyrphostin, protein tyrosine kinase inhibitors, significantly suppressed the Ang II-induced Ca²⁺ influx. Genistein and tyrphostin also suppressed the Ang II-induced formation of choline. These results suggest that Ang II stimulates phosphatidylcholine-hydrolyzing phospholipase D due to Ca²⁺ influx from the extracellular space in rat aortic SMC, and that protein tyrosine kinase is involved in the Ang II-induced Ca²⁺ influx, resulting in the promotion of phosphatidylcholine hydrolysis.