Integrin-mediated reduction in vascular smooth muscle [Ca2+](i) induced by RGD-containing peptide

It has previously been shown that synthetic peptides containing the sequence arginine-glycine-aspartic acid (RGD) cause vasodilation by activation of alpha(V) beta(3)-integrin present on vascular smooth muscle (VSM) cells. The purpose of this study was to determine whether this dilatory effect is mediated by a reduction in VSM cytosolic Ca2+ concentration ([Ca2+](i)). First-order arterioles from the rat cremaster were isolated, cannulated, and pressurized. [Ca2+](i) was quantitated from the ratio of emitted fluorescence intensity during alternate excitation of fura 2-loaded vessels at 340 and 380 nm. Cyclo(-Arg-Gly-Asp-D-Phe-Val) (cycloRGD; 0.21-210 mu M) produced a concentration-dependent dilation of arterioles that had developed basal myogenic tone. Over the entire concentration range tested, [Ca2+](i) decreased from 91 +/- 6 to 27 +/- 4 nM (69.7 +/- 5.0% reduction). In association with the decrease in [Ca2+](i), arteriolar lumen diameter increased from 89 +/- 8 to 184 +/- 8 mu m (89.8 +/- 1.8% dilation). At intermediate concentrations, cycloRGD induced rhythmic spiking of Ca2+ superimposed on the concentration-dependent lowering of basal [Ca2+](i). These data directly link integrin activation with alterations in Ca2+ regulation, the net effect of which is a reduction in [Ca2+](i). These data further suggest that integrins, through their role in mediating cellular attachment to the extracellular matrix and in cellular signaling involving Ca2+, could provide a logical link to mechanotransduction and myogenic phenomena.