Abstract 5830: Sphingosylphosphorylcholine is a Novel Trigger for Cholesterol-dependent Smooth Muscle Contraction Mediated by Rho-kinase in the Rat Basilar Artery
Hypercholesterolemia is a major risk factor in abnormal cerebrovascular events. Rho-kinase (ROK)-mediated Ca2+ sensitization of vascular smooth muscle (VSM) plays a pivotal role in cerebral vasospasm (CV). We previously showed that sphingosylphosphorylcholine (SPC), a sphingolipid, induces ROK-mediated Ca2+ sensitization in the bovine cerebral artery in vitro. Here, we show SPC-ROK-mediated VSM contraction in vivo and link this effect to cholesterol. Adult male Sprague-Dawley rats (400 –500g, n=45) received a control diet; a 1% cholesterol diet; or a 1% cholesterol diet + 5% β-cyclodextrin (β-CD), which depletes VSM cholesterol, for 8 weeks. Changes in the rat basilar artery (BA) diameter induced by KCl (118 mmol/L) or SPC (100 μmol/L) were measured using a cranial window preparation. Relaxation of the SPC-constricted BA with Y27632 (10 μmol/L), a ROK inhibitor, was also measured. The diameter of BA was used to calculate percentage reduction in diameter from the pretreatment artery. Serum total cholesterol (T-Cho) was measured using an L-type Wako CHO H kit. Statistical analysis was performed by Mann-Whitney U-test. Values are given as means±SD. SPC-induced VSM contraction was markedly reversed by Y27632 in rats fed a control diet (18.3±7.8%, n=24 vs. 1.94±9.3%, n=9, p<0.001). Serum T-Cho in rats fed a 1% cholesterol diet was significantly higher than in rats fed a control diet (131.8±20.0 mg/dl, n=16 vs. 53.6±10.7 mg/dl, n=24, p<0.001). SPC-induced contraction increased with the 1% cholesterol diet (36.4±7.9%, n=16, p<0.001 vs. control) and the extent of contraction correlated (r2=0.75, n=40) with serum T-Cho levels. SPC-induced contraction was reduced in rats fed a 1% cholesterol diet + 5% β-CD (8.3±4.8%, n=5, p<0.001 vs. 1% cholesterol diet group). KCL-induced vasocontraction did not differ significantly among the three diets. Vital signs were unchanged throughout the experiments. SPC may be a trigger for cholesterol-dependent VSM contractions mediated by ROK. However, the cholesterol-dependent pathway did not affect “normal and physiological” vascular contractions induced by membrane depolarization. Thus, the SPC-ROK pathway may initiate hypercholesterolemia-associated abnormal vascular contractions that are of importance in CV.