Enhanced responsiveness to angiotensin II in vascular smooth muscle cells from spontaneously hypertensive rats is not associated with alterations in protein kinase C

Abstract

This study compares vascular smooth muscle cells from spontaneously hypertensive and normotensive Wistar-Kyoto rats with respect to protein kinase C and intracellular responses to angiotensin II (Ang II). Ang II-induced degradation of polyphosphoinositides and accumulation of inositol di- and tris-phosphates was enhanced (~twofold) in hypertensive-derived cells, without a change (vs. normotensive-derived cells) in half-maximally effective concentrations of Ang II. Intracellular pH (~6.6) was comparable between both cell isolates at quiescence, but alkalinization induced by Ang II, serum, or phorbol ester was greater (Δ 0.1-0.2 pH units) for hypertensive-derived cells. For both cell types, the intracellular pH response to these agonists was prevented in the presence of Na+-H+ exchange inhibitors. S6 kinase activation induced by Ang II was enhanced (~twofold) in hypertensive-derived cells, whereas activation in response to serum or 12-O-tetradecanoylphorbol 13-acetate did not differ significantly between the two cell types. Quantitation of protein kinase C by immunoblotting and [3H]phorbol dibutyrate binding procedure revealed no differences between the two smooth muscle cell isolates (at quiescence or in the presence of serum) with respect to either total amounts or subcellular distribution. Sensitivity of protein kinase C to phorbol ester was apparently also not different between the two cell types, as assessed from dose-dependent (phorbol ester) S6 kinase activation profiles. Phorbol ester caused a similar subcellular redistribution of [3H]phorbol dibutyrate binding in the two cell isolates, but for both, minimal (10%) translocation occurred in response to Ang II. The data suggest that enhanced agonist responsiveness in vascular smooth msucle cells is unlikely to involve alterations in protein kinase C.