Cholesterol Primes Vascular Smooth Muscle to Induce Ca: Possible Role for Membrane Raft2+: Possible Role for Membrane Raft Sensitization Mediated by a Sphingosylphosphorylcholine–Rho-Kinase Pathway: Possible Role for Membrane Raft

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Hypercholesterolemia is a major risk factor involved in abnormal cardiovascular events. Rho-kinase–mediated Ca2+ sensitization of vascular smooth muscle (VSM) plays a critical role in vasospasm and hypertension. We recently identified sphingosylphosphorylcholine (SPC) and Src family tyrosine kinase (Src-TK) as upstream mediators for the Rho-kinase–mediated Ca2+ sensitization. Here we report the strong linkage between cholesterol and the Ca2+ sensitization of VSM mediated by a novel SPC/Src-TK/Rho-kinase pathway in both humans and rabbits. The extent of the sensitization correlated well with the total cholesterol or low-density lipoprotein cholesterol levels in serum. However, an inverse correlation with the serum level of high-density lipoprotein cholesterol was observed, and a correlation with other cardiovascular risk factors was nil. When cholesterol-lowering therapy was given to patients and rabbits with hypercholesterolemia, the SPC-induced contractions diminished. Depletion of VSM cholesterol by β-cyclodextrin resulted in a loss of membrane caveolin-1, a marker of cholesterol-enriched lipid raft, and inhibited the SPC-induced Ca2+ sensitization and translocation of Rho-kinase from cytosol to the cell membrane. Vasocontractions induced by membrane depolarization and by an adrenergic agonist were cholesterol-independent. Our data support the previously unreported concept that cholesterol potentiates the Ca2+ sensitization of VSM mediated by a SPC/Src-TK/Rho-kinase pathway, and are also compatible with a role for cholesterol-enriched membrane microdomain, a lipid raft. This process may play an important role in the development of abnormal vascular contractions in patients with hypercholesterolemia.

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