Rho-kinase, but not protein kinase C, is involved in generation of the spontaneous tone in the resting phase of the isolated pig iris sphincter muscle.
OBJECTIVE
The purpose of the present study was to clarify the role of Rho-kinase and/or protein kinase C in the resting tension of the isolated pig iris sphincter muscle.


METHODS
The motor activity of the isolated pig iris sphincter muscle was measured isometrically.


RESULTS
EGTA, a chelator of extracellular Ca(2+), significantly reduced the resting tension. Y27632, a Rho-kinase inhibitor, significantly reduced the resting tension in a concentration-dependent manner. The resting tension diminished by Y27632 was significantly recovered by the addition of calyculin A, a myosin light chain phosphatase (MLCP) inhibitor, in a concentration-dependent manner. GF109203X, a protein kinase C inhibitor, had no effect on the resting tension.


CONCLUSIONS
These results suggest that, in the isolated pig iris sphincter muscle, Rho-kinase plays an important role in the generation of spontaneous tone in the resting phase via the inhibition of MLCP activity.
Okano
Mayumi
M
Department of Orthoptics and Visual Sciences, School of Health Sciences, Kyushu University of Health and Welfare, Nobeoka, Miyazaki, Japan.
Uchikawa
Yoshikazu
Y
Tanaka
Naoko
N
Mutoh
Junpei
J
Ohkura
Masamichi
M
Hisa
Hiroaki
H
Yamamoto
Ryuichi
R
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007498:Iris / Q000201:enzymology*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology*; D043263:Myosin-Light-Chain Phosphatase / Q000037:antagonists & inhibitors / Q000502:physiology; D010275:Parasympathetic Nervous System / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D011680:Pupil / Q000502:physiology; D013552:Swine; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*
D004791:Enzyme Inhibitors; D054460:rho-Associated Kinases; D011493:Protein Kinase C; D043263:Myosin-Light-Chain Phosphatase