Sphingosylphosphorylcholine Is a Novel Messenger for Rho-Kinase–Mediated Ca Sensitization in the Bovine Cerebral Artery Unimportant Role for Protein Kinase C

Although recent investigations have suggested that a Rho-kinase–mediated Ca sensitization of vascular smooth muscle contraction plays a critical role in the pathogenesis of cerebral and coronary vasospasm, the upstream of this signal transduction has not been elucidated. In addition, the involvement of protein kinase C (PKC) may also be related to cerebral vasospasm. We recently reported that sphingosylphosphorylcholine (SPC), a sphingolipid, induces Rho-kinase–mediated Ca sensitization in pig coronary arteries. The purpose of this present study was to examine the possible mediation of SPC in Ca sensitization of the bovine middle cerebral artery (MCA) and the relation to signal transduction pathways mediated by Rho-kinase and PKC. In intact MCA, SPC induced a concentration-dependent (EC5053.0 mmol/L) contraction, without [Ca ]i elevation. In membrane-permeabilized MCA, SPC induced Ca 21 sensitization even in the absence of added GTP, which is required for activation of G-proteins coupled to membrane receptors. The SPC-induced Ca sensitization was blocked by a Rho-kinase inhibitor (Y-27632) and a dominantnegative Rho-kinase, but not by a pseudosubstrate peptide for conventional PKC, which abolished the Ca-independent contraction induced by phorbol ester. In contrast, phorbol ester–induced Ca sensitization was resistant to a Rho-kinase inhibitor and a dominant-negative Rho-kinase. In primary cultured vascular smooth muscle cells, SPC induced the translocation of cytosolic Rho-kinase to the cell membrane. We propose that SPC is a novel messenger for Rho-kinase–mediated Ca sensitization of cerebral arterial smooth muscle and, therefore, may play a pivotal role in the pathogenesis of abnormal contraction of the cerebral artery such as vasospasm. The SPC/Rho-kinase pathway functions independently of the PKC pathway. (Circ Res. 2002;91:●●●-●●●.)