Possible involvement of Rho kinase in Ca2+ sensitization and mobilization by MCh in tracheal smooth muscle

We examined the effects of Rho kinase on contraction and intracellular Ca2+ concentration ([Ca2+](i)) in guinea pig trachealis by measuring isometric force and the fura 2 signal [340- to 380-nm fluorescence ratio (F340/F380)]. A Rho kinase inhibitor, Y-27632 (1-1,000 muM), inhibited methacholine (MCh)-induced contraction, with a reduction in F340/F380 in a concentration-dependent manner. The values of EC50 for contraction and F340/F380 induced by 1 muM MCh with Y-27632 were 27.3 +/- 5.1 and 524.1 +/- 31.0 muM, respectively. With 0.1 muM MCh, the values for these parameters were decreased to 1.0 +/- 0.1 and 98.2 +/- 6.2 muM, respectively. Tension-F340/F380 curves for MCh indicated that Y-27632 caused an similar to 50% inhibition of MCh-induced contraction, without a reduction in F340/F380. These effects of Y-27632 were not inhibited by a protein kinase C inhibitor, GF-109203X. Our results indicate that inhibition of Rho kinase attenuates both Ca2+ sensitization and [Ca2+](i).