Role of Ca2+-dependent and Ca2+-sensitive mechanisms in sphingosine 1-phosphate-induced constriction of isolated porcine retinal arterioles in vitro

- We examined the effect of Sphingosine 1-phosphate (S1P) on retinal arterioles.
- S1P elicits vasoconstriction of the retinal arterioles via S1P Receptor 2.
- Ca2+-sensitization pathway plays a role in the S1P-induced vasoconstriction.
- Ca2+-dependent pathway also plays a role in the S1P-induced vasoconstriction.

Although sphingosine 1-phosphate (S1P), a bioactive lipid derived from activated platelets, has a variety of physiologic effects on vessels, no reports have described the effect of S1P on the retinal circulation. We examined the effect and underlying mechanism of the vasomotor action of S1P on porcine retinal arterioles. The porcine retinal arterioles were isolated, cannulated, and pressurized without flow for in vitro study. S1P-induced diameter changes were recorded using videomicroscopic techniques. S1P elicited concentration-dependent (1 nM-10 μM) vasoconstriction of the retinal arterioles that was abolished by the S1P receptor 2 (S1PR2) antagonist JTE-013. S1P-induced vasoconstriction was abolished by the Rho kinase (ROCK) inhibitor H-1152 and was inhibited partly by the protein kinase C (PKC) inhibitor Gö-6983. The inhibition of phospholipase C by U73122 and L-type voltage-operated calcium channels (L-VOCCs) by nifedipine inhibited S1P-induced vasoconstriction; a combination of both inhibitors abolished S1P-induced vasoconstriction. Furthermore, inhibition of myosin light chain kinase (MLCK) by ML-9 significantly blocked S1P-induced vasoconstriction; further coadministration of ML-9 with H-1152 or Gö-6983 abolished S1P-induced vasoconstriction. The current data suggest that S1P elicits vasoconstriction of the retinal arterioles via S1PR2 in vascular smooth muscle cells and this vasoconstriction may be mediated by the Ca2+-sensitive pathway via activation of PKC leading to activation of ROCK and the Ca2+-dependent pathway via activation of L-VOCCs resulting in activation of MLCK.