Fengling Guo

Cholesterol Primes Vascular Smooth Muscle to Induce Ca2 Sensitization Mediated by a Sphingosylphosphorylcholine–Rho-Kinase Pathway Possible Role for Membrane Raft

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 &bgr;-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.

Sivelestat Relaxes Porcine Coronary Artery via Inhibition of Ca2+ Sensitization Induced by a Receptor Agonist

Sivelestat sodium hydrate (sivelestat) is a novel synthetic drug and specific inhibitor of neutrophil elastase that has been approved in Japan as a treatment for acute lung injury associated with systemic inflammatory response syndrome. There are no reports on the effects of sivelestat on the contractile regulation of vascular smooth muscle. The purpose of the present study was to assess the effects of sivelestat on porcine coronary artery. Sivelestat induced concentration-dependent (3 × 10−5 to 3 × 10−4 M) vasorelaxation in U46619 (100 nM)-precontracted porcine coronary artery with or without endothelium. Simultaneous measurements of tension and the cytosolic Ca2+ concentration ([Ca2+]i) revealed that sivelestat shifted the [Ca2+]i-tension curve to the right and downward during stimulation with 118 mM K+ and 100 nM U46619. In β-escin-permeabilized arterial strips, sivelestat abolished GTP plus U46619-induced contractions at constant [Ca2+]i, whereas it had no effect on Ca2+-induced contractions. Thus, sivelestat relaxes porcine coronary artery smooth muscle via the selective inhibition of Ca2+ sensitization induced by a receptor agonist, without affecting Ca2+-induced contraction.