Rho-kinase inhibitors augment the inhibitory effect of propofol on rat bronchial smooth muscle contraction.

Background: Airway smooth muscle contraction is not caused by the increase in intracellular Ca(2+) ([Ca(2+)](i)) alone because agonist stimulation increases tension at the same [Ca(2+)](i) (increase in Ca(2+) sensitivity). The small G protein Rho A and Rho-kinase (ROCK) play important roles in the regulation of Ca(2+) sensitivity. In this study, we investigated the effects of three ROCK inhibitors (fasudil, Y-27632, and H-1152) on rat airway smooth muscle contraction and the effects of ROCK inhibitors on propofol-induced bronchodilatory effects.

Methods: Ring strips from intrapulmonary bronchus of male Wistar rats were placed in 400-microL organ baths containing Krebs-Henseleit solution. After obtaining stable contraction with 30 microM acetylcholine, (1) propofol (1 microM-1 mM) was cumulatively applied; (2) cumulative doses of Y-27632 (0.01-300 microM), fasudil (0.01-100 microM), or H-1152 (0.01-100 microM) were applied; (3) propofol (1 microM-1 mM), with Y-27632, fasudil or H-1152 (0.03 microM or 0.1 microM), was cumulatively applied.

Results: (1) Propofol produced concentration-dependent relaxation of rat bronchial smooth muscle. (2) All ROCK inhibitors produced concentration-dependent relaxation. (3) 0.03 microM Y-27632 and fasudil had no significant effect on the concentration-response curve for propofol, while 0.1 microM of both agents significantly shifted concentration-response curves to the left and decreased EC(50). H-1152 (both 0.03 microM and 0.1 microM) significantly sifted the concentration-response curve for propofol to the left and decreased EC(50).

Conclusions: ROCK inhibitors, especially H-1152, can attenuate the contraction of rat airway smooth muscle. The combined use of ROCK inhibitors and propofol causes greater relaxation.