Src family kinase involvement in rat preglomerular microvascular contractile and [Ca2+]i responses to ANG II

Experiments were performed to investigate the potential role of Src family kinase(s) in the rat afferent arteriolar contractile response to ANG II. The in vitro blood- perfused juxtamedullary nephron technique was employed to monitor afferent arteriolar lumen diameter responses to 1-100 nM ANG II before and during Src family kinase inhibition (10 muM PP2). PP2 did not alter baseline diameter but attenuated ANG II-induced contractile responses by 33 +/- 6%. An inactive analog of PP2 (PP3) had no effect on ANG II-induced afferent arteriolar contraction. The effect of Src kinase inhibition on ANG II- induced intracellular free Ca2+ concentration ([Ca2+](i)) responses was probed in fura 2-loaded preglomerular microvascular smooth muscle cells (PVSMCs) obtained from explants and studied after 3-5 days in culture. In untreated PVSMCs, ANG II evoked peak (Delta = 293 +/- 66 nM) and plateau (Delta = 23 +/- 8 nM) increases in [Ca2+](i). In PVSMCs pretreated with PP2, baseline [Ca2+](i) was unaltered, but both the peak (Delta = 140 +/- 22 nM) and plateau (Delta = 3 +/- 2 nM) phases of the ANG II response were significantly reduced compared with untreated cells. PP3 did not alter [Ca2+](i) responses to ANG II. Immunoprecipitation and Western blot analysis confirmed that 100 nM ANG II increased phosphorylation of c-Src (at Y-416) in PVSMCs. The phosphorylation response was maximal 1 min after ANG II exposure and was prevented by PP2. We conclude that the preglomerular vasoconstriction evoked by ANG II involves rapid c-Src activation with subsequent effects that contribute to the [Ca2+](i) response to the peptide.