Abstract
Sphingosine-1-phosphate (S1P) constricts cerebral arteries through S1P(3) receptor stimulation. Because the activity of the key S1P-synthesizing enzyme, sphingosine kinase (SPK), can be stimulated by agonists of various G protein-coupled receptors, it is likely that S1P also acts as a second messenger for other vasoconstrictors. We investigated the effect of SPK inhibitors and SPK gene deletion on the contractile responses of isolated vessels to vasoactive agonists and KCl-induced depolarization. Basilar and femoral arteries of rat, mounted in a wire myograph, were incubated with dimethylsphingosine (DMS), 2-(p-hydroxyanilino)-4-(p-chlorophenyl) thiazole (Compound 2) or FTY720, and exposed to KCl, 5-hydroxytryptamine (5-HT), S1P or phenylephrine (PE). Vasomotor responses in basilar artery were decreased by DMS, Compound 2 and FTY720, while they were not affected in femoral artery. Basilar arteries from SPK1(-/-) mice exhibited weaker vasoconstriction to both KCl and agonists (S1P and the prostanoid U46619) when compared to either wild type (WT) or SPK2(-/-). In contrast, in mesenteric resistance arteries, neither the contraction to KCl nor the maximum contraction to PE and S1P significantly differed among WT, SPK1(-/-) and SPK2(-/-). Quantitative analysis of SPK mRNA (reverse transcription and real time polymerase chain reaction) in mouse arteries showed 40-80-fold higher SPK1 expression in cerebral arteries than in aorta or mesenteric arteries. SPK1 critically modulates the reactivity of cerebral vasculature to vasoconstrictors. S1P plays a specific role as modulator of cerebral blood flow, potentially acting either directly outside vascular smooth muscle cells on S1P(3) receptors, or indirectly after being generated inside the cell in response to vasoconstrictors.