Sphingosylphosphorylcholine (SPC), a sphingolipid, concentration-dependently (1–50 μM) induced contraction and slight elevation of the cytosolic Ca2+ concentration ([Ca2+]i) in smooth muscle of the pig coronary artery, the result being a marked increase in the force/[Ca2+]i ratio. In α-toxin- or β-escin-permeabilized, but not Triton X-100-permeabilized, vascular strips, SPC induced contraction at constant [Ca2+]i (pCa 6.3) in the absence of GTP, whereas a G-protein-coupled receptor agonist, histamine, required the presence of GTP to induce the contraction. The Rho-kinase blocker, Y-27632 (10 μM) abolished the SPC-induced Ca2+-sensitization, without affecting the Ca2+-induced contraction. These results suggest that SPC induces Ca2+-sensitization of force in vascular smooth muscle, presumably through the activation of Rho-kinase (or a related kinase).
