The inhibitory mechanism of EPA on the SPC/Fyn/ROK-mediated abnormal vascular smooth muscle contraction, in which membrane rafts are involved

Abstract

Rho-kinase (ROK)-mediated Ca²⁺sensitization of vascular smooth muscle (VSM) plays a critical role in abnormal VSM contraction such as vasospasm. We previously found that sphingosylphosphorylcholine (SPC) induced ROK-mediated Ca²⁺sensitization of VSM through the activation of Fyn, and eicosapentaenoic acid (EPA) selectively inhibited the Ca²⁺sensitization by blocking the activation of Fyn. In this study, we examined the inhibitory mechanism of EPA on the SPC-induced Ca²⁺sensitization. SPC induced VSM contraction with no elevation of cytosolic Ca²⁺ concentration ([Ca²⁺]_i), and EPA inhibited the SPC-induced contraction without affecting the high-K-depolarization-induced contraction and [Ca²⁺]_i elevation. In cultured VSM cells, SPC induced the translocations of Fyn and ROK to plasma membrane, where they were colocalized with membrane raft markers, caveolin-1 and cholera toxin subunit B. EPA inhibited the SPC-induced translocation of Fyn and ROK without affecting the localization of caveolin-1, whereas β-cyclodextrin, which selectively deprived membrane cholesterol and thereby removed caveolin-1 from plasma membrane, inhibited the SPC-induced translocation of Fyn and ROK and contraction. Those findings suggest that membrane rafts plays a pivotal role in the Ca²⁺sensitization mediated by SPC/Fyn/ROK pathway, and EPA blocks this pathway without affecting membrane raft property. [J Physiol Sci. 2007;57 Suppl:S86]