Desensitization and muscarinic re-sensitization of force and myosin light chain phosphorylation to cytoplasmic Ca2+ in smooth muscle.
In alpha-toxin-permeabilized guinea-pig ileum smooth muscle, a step increase in Ca2+ caused a rapid rise in force and myosin light chain (LC20) phosphorylation, followed by their spontaneous decline to a low steady level even though Ca2+ remained constant. Carbachol resensitized the muscles to Ca2+, causing an increase in both the steady state force and LC20 phosphorylation at constant Ca2+. In beta-escin permeabilized preparations, calmodulin and okadaic acid converted the phasic responses to Ca2+ to more tonic ones. We conclude that Ca2(+)-sensitivity of force is modulated through changes in LC20 kinase/phosphatase activity ratio by Ca2+ itself (desensitization) and by agonists (sensitization).
Kitazawa
T
T
Department of Physiology, University of Virginia School of Medicine, Charlottesville 22908.
Somlyo
A P
AP
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003593:Cytoplasm / Q000187:drug effects; D004928:Escin / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D019319:Okadaic Acid; D010277:Parasympathomimetics / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011817:Rabbits
D002147:Calmodulin; D004988:Ethers, Cyclic; D010277:Parasympathomimetics; D019319:Okadaic Acid; D004928:Escin; D006632:Histamine; D002217:Carbachol; D009218:Myosins; D002118:Calcium