Abstract
Hypercholesterolemia is a major risk factor of cardiovascular events. A Rho-kinase (ROK)-mediated Ca2+ sensitization of vascular smooth muscle (VSM) plays a critical role in abnormal VSM contraction such as vasospasm. We found that SPC activates this pathway, dependently on cholesterol in the VSM tissues and cells and through the activation of Fyn. These results, taken together with the localization of Fyn in cholesterol-enriched membrane microdomains, membrane lipid rafts, suggest the essential roles of membrane rafts in abnormal VSM contraction. Although several signaling molecules, such as receptors or kinases, accumulate membrane rafts, the membrane-permeabilization of VSM revealed that the activation of G-proteins or GPCRs was not required for the SPC-induced contraction. Therefore, we aimed to investigate the possible interaction of SPC with membrane lipid rafts. For this purpose, we successfully and originally developed the model membrane lipid rafts, which contain high concentrations of cholesterol and sphingomyelin, and examined their direct interaction with SPC, using the surface plasmon resonance measurement (BIACORE system). Here we provide the first direct evidence that SPC has very high affinity for the model membrane lipid rafts, but very weak affinity for the normal control model membrane, containing mainly phosphatidylcholine. This notion also supports the important roles of cholesterol and its enriched membrane, lipid rafts. [J Physiol Sci. 2008;58 Suppl:S204]
