mRNA transcripts encoding sphingosine kinase, S1P phosphohydrolase and three S1P receptors (S1P(1-3)) were detected in the SMA. S1P induced dose-dependent vasoconstriction of the SMA (EC50 = 115 nmol/L), and enhanced the apparent Ca2+-sensitivity of the contractile apparatus. Noradrenaline did not elicit vasoconstriction. The Rho kinase inhibitor Y27632 (1 micromol/L) reversed S1P-induced vasoconstriction and the S1P-mediated enhancement of Ca2+-sensitivity