The proposed project will investigate the role of ion fluxes in vascular smooth muscle cell proliferation. Vascular smooth muscle cell proliferation can be stimulated by growth factors (e.g., platelet-derived growth factor), phorbol esters (e.g., 12-0-tetradecanoyl phorbol-13-acetate), and evalations in cyclic AMP (cAMP). In addition to stimulating DNA synthesis, these agents also activate Na/H exchange in vascular smooth muscle cells. Under certain experimental conditions, cAMP also has antiproliferative activity as does the glycosaminoglycan, heparin. It is hypothesized that agents which regulate DNA synthesis in vascular smooth muscle cells do so via effects on ion fluxes such as intracellular Ca levels or Na/H exchange. In the present proposal the relationship between Na/H exchange and DNA synthesis will be probed by determining the effect of blocking Na/H exchange on DNA synthesis, by evaluating the mechanism of heparin inhibition of DNA synthesis (i.e., does heparin inhibit Na/H exchange?), and by correlation of growth factor stimulated Na/H exchange and DNA synthesis. In addition, the mechanism of activation of Na/H exchange by mitogens will be investigated. In these studies, phosphoinositide turnover will be measured and the effect of platelet-derived growth factor and inositol triphosphate on intracellular calcium levels will be evaluated. Finally, the role of cAMP in VSMC proliferation will be determined. Thus, experiments are designed to evaluate cAMP levels throughout the cell cycle, to test the theory that a discrete burst of cAMP is required for DNA synthesis and to assess the effects of cAMP on Ca levels and on Na/H exchange. These studies should provide basic information regarding the mechanism of vascular smooth muscle cell proliferation. These findings may be important in understanding the underlying mechanisms involved in atheromatous plaque formation.
