Myosin light chain kinase and Rho-kinase participate in P2Y receptor-mediated acceleration of permeability through the endothelial cell layer.

We have shown that P2Y receptor stimulation accelerates macromolecular permeation through the endothelial cell layer. To elucidate the mechanism of this acceleration, we examined the effects of ML-9, a myosin light chain kinase inhibitor, and Y-27632, a Rho-kinase inhibitor, on fluorescein isothiocyanate dextran (FD-4) permeation across the human umbilical vein endothelial cell monolayer. FD-4 permeation was analysed by high-performance liquid chromatography fluorescence detection. A P2Y receptor agonist, 2meS-ATP, enhanced the permeability of FD-4, which was inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a P2Y-receptor antagonist. The 2meS-ATP-induced increase in the permeability of FD-4 was significantly inhibited by ML-9. Also, Y-27632 prevented the 2meS-ATP-induced increase in the permeability of FD-4. Neither ML-9 nor Y-27632 influenced the spontaneous permeation of FD-4. These results suggest that phosphorylation of the myosin light chain may play an important role in the purinergic regulation of macromolecular permeation through the vascular endothelium.