Augmented sphingosylphosphorylcholine-induced Ca²⁺-sensitization of mesenteric artery contraction in spontaneously hypertensive rat

Sphingosylphosphorylcholine (SPC) is a vasoconstricting lysosphingolipid, and the RhoA/Rho-kinase pathway plays an important role in SPC-induced contraction. Since RhoA/Rho-kinase-mediated signaling is involved in the generation and/or maintenance of hypertension, we compared the effect of SPC on the contractility of endothelium-denuded small mesenteric arteries in spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Fura-2 Ca²⁺ signals, contractile responses, and phosphorylation of 20-kDa myosin light chains (MLC₂₀) were measured. Ten μM SPC induced a gradual and sustained vasoconstriction, which was greater in arteries of the SHR (82.5±4.3%, n=9) than in those of the WKY (26.7±4.5%, n=10). In Ca²⁺-free media, SPC gradually increased vascular tone in the SHR, but caused little vasoconstriction in the WKY. In the SHR and WKY, SPC evoked a greater vasoconstriction than did high K⁺ depolarization at a given Ca²⁺ ratio, and the Ca²⁺ ratio - tension curve induced by SPC was significantly shifted to the left compared with that induced by high K⁺ depolarization. However, the magnitude of shift to the left was greater in the SHR than in the WKY. The Rho-kinase inhibitor Y-27632 significantly inhibited SPC-induced contractions, but neither the protein kinase C inhibitor calphostin-C nor PD98059, which inhibits activation of some mitogen-activated protein kinases, had any effect on the SHR or the WKY. SPC significantly increased the phosphorylation of MLC₂₀ in both the SHR and the WKY, and Y-27632 inhibited the SPC-induced increase in MLC₂₀ phosphorylation in the SHR. Our results suggest that SPC induces greater vascular tone in the SHR than in the WKY. Furthermore, our results indicate that activation of the Rho-kinase pathway plays an important role in the SPC-induced Ca²⁺ sensitization in the SHR.