Ca2+ can control vascular smooth-muscle thin filaments without caldesmon phosphorylation.
The Ca2+-dependent regulation of the activation of myosin MgATPase by vascular-smooth-muscle thin filaments involves caldesmon. This effect may be due to the direct interaction of caldesmon with a Ca2+-binding protein such as calmodulin or phosphorylation of caldesmon by a Ca2+-dependent kinase. I have found that Ca2+ switches on aorta thin filaments in less than 10 s, whereas the caldesmon in the thin filaments is phosphorylated only slowly (half-time greater than 10 min) and the maximum phosphorylation is very low (1 molecule per 7 molecules of caldesmon). I conclude that the phosphorylation of caldesmon hypothesis is untenable.
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000199:Actins / Q000494:pharmacology; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D010766:Phosphorylation; D012756:Sheep; D014335:Tropomyosin / Q000494:pharmacology
D000199:Actins; D002148:Calmodulin-Binding Proteins; D014335:Tropomyosin; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D002118:Calcium