Rho-kinase inhibition and electromechanical coupling in rat and guinea-pig ureter smooth muscle: Ca2+-dependent and -independent mechanisms.
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.
Shabir
S
S
Department of Physiology, The University of Liverpool, Liverpool L69 3BX, UK.
Borisova
L
L
Wray
Susan
S
Burdyga
T
T
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051381:Rats; D014513:Ureter / Q000187:drug effects / Q000502:physiology*; D054460:rho-Associated Kinases
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases