Rho-kinase inhibition and electromechanical coupling in rat and guinea-pig ureter smooth muscle: Ca2+-dependent and -independent mechanisms

• Published in: The Journal of physiology 2004-11, Vol.560 (3), p.839-855
• Main Authors: Shabir, S., Borisova, L., Wray, Susan, Burdyga, T.
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Animals; Calcium Channels - physiology; Calcium Signaling - drug effects; Calcium Signaling - physiology; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Guinea Pigs; In Vitro Techniques; Intracellular Signaling Peptides and Proteins; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle Relaxation - drug effects; Muscle Relaxation - physiology; Muscle, Smooth - drug effects; Muscle, Smooth - physiology; Protein-Serine-Threonine Kinases - antagonists & inhibitors; Protein-Serine-Threonine Kinases - metabolism; Rats; Research Papers; rho-Associated Kinases; Ureter - drug effects; Ureter - physiology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2004.070615

Recent data have shown Ca 2+ -dependent activation of Rho-kinase by sustained depolarization of arterial smooth muscle. Visceral smooth muscles, however, contract phasically in response to action potentials and it is unclear whether Ca 2+ -dependent or -independent Rho-kinase activation occurs. We have therefore investigated this, under physiologically relevant conditions, in intact ureter. Action potentials, ionic currents, Ca 2+ transients, myosin light chain (MLC) phosphorylation and phasic contraction evoked by action potentials in guinea-pig and rat ureter were investigated. In rat, but not guinea-pig ureter, three Rho-kinase inhibitors, Y-27632, HA-1077 and H-1152, significantly decreased phasic contractions and Ca 2+ transients. Voltage- and current-clamp data showed that Rho-kinase inhibition reduced the plateau component of the action potential, inhibited Ca 2+ -channels and, indirectly, Ca 2+ -activated Cl − channels. The Ca 2+ channel agonist Bay K8644 could reverse these effects. The K + channel blocker TEA could also reverse the inhibitory effect of Y-27632 on the action potential and Ca 2+ transient. Ca 2+ transients and inward current, activated by carbachol-induced sarcoplasmic reticulum Ca 2+ release, were not affected by Rho-kinase inhibition. Rho-kinase inhibition produced a Ca 2+ -independent increase in the relaxation rate of contraction, associated with acceleration of MLC dephosphorylation, which was sensitive to calyculin A. These data show for the first time that: (1) Rho-kinase has major effects on Ca 2+ signalling associated with the action potential, (2) this effect is species dependent and (3) Rho-kinase controls relaxation of phasic contraction of myogenic origin. Thus Rho-kinase can modulate phasic smooth muscle in the absence of agonist, and the mechanisms are both Ca 2+ -dependent, involving ion channels, and Ca 2+ -independent, involving MLC phosphorylation activity.