Abstract
Hypercholesterolemia is a major risk factor of cardiovascular events. A Rho-kinase-mediated Ca2+ sensitization of vascular smooth muscle (VSM) plays a critical role in abnormal vascular contraction such as vasospasm. We found that sphingosylphosphorylcholine (SPC) sequentially activated Fyn and Rho-kinase to induce the Ca2+ sensitization. We observed the strong link between the SPC-induced contraction and the tissue and cellular cholesterol in VSM, suggesting the involvement of the cholesterol-enriched membrane microdomains, membrane lipid rafts. In membrane-permeabilized VSM, SPC induced contraction in the absence of cytosolic GTP which is required for the activation of G-proteins and thus of GPCRs. Taken together with the localization of Fyn in the membrane lipid rafts, these findings suggest the importance of cholesterol and are compatible with the interaction of SPC with the other membrane components than GPCRs and/or the direct interaction between SPC and lipid membrane, which may in turn affects the function of membrane proteins. Therefore, we examined the interaction of SPC with raft model membranes. The surface plasmon resonance measurement (BIACORE system) revealed that SPC highly associates with the model membrane microdomains, lipid rafts and that cholesterol in the model membrane enhances the incorporation of SPC into the membrane. We propose that cholesterol and its enriched membrane lipid rafts may play a role in Ca2+ sensitization mediated by a SPC-Fyn-Rho kinase pathway. [J Physiol Sci. 2006;56 Suppl:S117]
