Contribution of Rho‐kinase to membrane excitability of murine colonic smooth muscle

BACKGROUND AND PURPOSE The Rho‐kinase pathway regulates agonist‐induced contractions in several smooth muscles, including the intestine, urinary bladder and uterus, via dynamic changes in the Ca 2+ sensitivity of the contractile apparatus. However, there is evidence that Rho‐kinase also modulates other cellular effectors such as ion channels. EXPERIMENTAL APPROACH We examined the regulation of colonic smooth muscle excitability by Rho‐kinase using conventional microelectrode recording, isometric force measurements and patch‐clamp techniques. KEY RESULTS The Rho‐kinase inhibitors, Y‐27632 and H‐1152, decreased nerve‐evoked on‐ and off‐contractions elicited at a range of frequencies and durations. The Rho‐kinase inhibitors decreased the spontaneous contractions and the responses to carbachol and substance P independently of neuronal inputs, suggesting Y‐27632 acts directly on smooth muscle. The Rho‐kinase inhibitors significantly reduced the depolarization in response to carbachol, an effect that cannot be due to regulation of Ca 2+ sensitization. Patch‐clamp experiments showed that Rho‐kinase inhibitors reduce GTPγS‐activated non‐selective cation currents. CONCLUSIONS AND IMPLICATIONS The Rho‐kinase inhibitors decreased contractions evoked by nerve stimulation, carbachol and substance P. These effects were not solely due to inhibition of the Ca 2+ sensitization pathway, as the Rho‐kinase inhibitors also inhibited the non‐selective cation conductances activated by excitatory transmitters. Thus, Rho‐kinase may regulate smooth muscle excitability mechanisms by regulating non‐selective cation channels as well as changing the Ca 2+ sensitivity of the contractile apparatus.