Comparison of sphingosine 1-phosphate-induced intracellular signaling pathways in vascular smooth muscles: differential role in vasoconstriction

Sphingosine 1-phosphate (S1P), a lipid released from activated platelets, influences physiological processes in the cardiovascular system via activation of the endothelial differentiation gene (EDG/S1P) family of 7 transmembrane G protein-coupled receptors. In cultured vascular smooth muscle (VSM) cells, S1P signaling has been shown to stimulate proliferative responses; however, its role in vasoconstriction has not been examined. In the present study, the effects of S1P and EDG/S1P receptor expression were determined in rat VSM from cerebral artery and aorta. S1P induced constriction of cerebral artery, which was partly dependent on activation of p160(ROCK) (Rho-kinase). S1P also induced activation of RhoA in cerebral artery with a similar time course to contraction. In aorta, S1P did not produce a constriction or RhoA activation. In VSM myocytes from cerebral arteries, stimulation with S1P gives rise to a global increase in [Ca2+](i), initially generated via Ca2+ release from the sarcoplasmic reticulum by an inositol 1,4,5-trisphosphate- dependent pathway. In aorta VSM, a small increase in [Ca2+](i) was observed after stimulation at higher concentrations of S1P. S1P induced activation of p42/p44(mapk) in aorta and cerebral artery VSM. Subtype-specific S1P receptor antibodies revealed that the expression Of S1P(3)/EDG-3 and S1P(2)/EDG-5 receptors is 4-fold higher in cerebral artery compared with aorta. S1P(1)/EDG-1 receptor expression was similar in both types of VSM. Therefore, the ability of SIP to act as a vasoactive mediator is dependent on the activation of associated signaling pathways and may vary in different VSM. This differential signaling may be related to the expression of S1P receptor subtypes.