Integrin mobilizes intracellular Ca2+ in renal vascular smooth muscle cells

Peptides with the Arg-Gly-Asp (RGD) motif induce vasoconstriction in rat afferent arterioles by increasing the intracellular Ca2+ concentration ([Ca2+](i)) in vascular smooth muscle cells (VSMC). This finding suggests that occupancy of integrins on the plasma membrane of VSMC might affect vascular tone. The purpose of this study was to determine whether occupancy of integrins by exogenous RGD peptides initiates intracellular Ca2+ signaling in cultured renal VSMC. When smooth muscle cells were exposed to 0.1 mM hexapeptide GRGDSP, [Ca2+](i) rapidly increased from 91 +/- 4 to 287 +/- 37 nM and then returned to the baseline within 20 s (P< 0.05, 34 cells/5 coverslips). In controls, the hexapeptide GRGESP did not trigger Ca2+ mobilization. Local application of the GRGDSP induced a regional increase of cytoplasmic [Ca2+](i), which propagated as Ca2+ waves traveling across the cell and induced a rapid elevation of nuclear [Ca2+](i). Spontaneous recurrence of smaller-amplitude Ca2+ waves were found in 20% of cells examined after the initial response to RGD-containing peptides. Blocking dihydropyridine-sensitive Ca2+ channels with nifedipine or removal of extracellular Ca2+ did not inhibit the RGD-induced Ca2+ mobilization. However, pretreatment of 20 mM ryanodine completely eliminated the RGD-induced Ca2+ mobilization. Anti-<beta>(1) and anti-beta (3)-integrin antibodies with functional blocking capability simulate the effects of GRGDSP in [Ca2+](i). Incubation with anti-beta (1)- or beta (3)-integrin antibodies inhibited the increase in [Ca2+](i) induced by GRGDSP. We conclude that exogenous RGD-containing peptides induce release of Ca2+ from ryanodine-sensitive Ca2+ stores in renal VSMC via integrins, which can trigger cytoplasmic Ca2+ waves propagating throughout the cell.