title: Exogenous calmodulin increases Ca2+ sensitivity of isometric tension activation and myosin phosphorylation in skinned smooth muscle.
abstract: We have investigated the effect of exogenous calmodulin on chicken gizzard or rabbit ileum smooth muscle functionally skinned by mechanical grinding or exposure to Triton X-100 detergent. We found that specific protein inhibitor, modulator binding protein, caused a loss of Ca2+-activated tension which was restored by subsequent treatment with calmodulin. Calmodulin at 5 microM increased 10-fold the speed of development of isometric tension while it had no significant effect on the rate of relaxation or on maximum tension at high Ca2+ concentrations. The Ca2+ sensitivity of steady state tension and LC20 phosphorylation were also increased by 5 microM calmodulin. These results are consistent with a calmodulin-regulated light chain kinase/phosphatase system being responsible for activation of tension in smooth muscle.
mesh_terms: D000818:Animals; D001711:Biotransformation; D002118:Calcium / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002645:Chickens; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000378:metabolism; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D009218:Myosins / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D009124:Muscle Proteins; D009218:Myosins; D002118:Calcium