Cross-Bridge Cycle in Phasic and Tonic Smooth Muscle

摘要: Comparison of the cross-bridge cycle and its regulation in phasic tonic smooth muscles reveals following: (1) ATP binding detachment cross-bridges by is fast not rate-limiting to overall catalytic cycle. (2) The rate force development faster than under two physiologic conditions: (a) when myosin light chain (MLC20) phosphorylation rate-limiting; (b) thiophosphorylated muscle which actomyosin reactions are rate-limiting. (3) MLC20 kinase phosphatase activities higher muscle. (4) MgADP, at concentrations thought be within range, reduces amplitude rapid component prolongs slow relaxation from rigor, whereas inorganic phosphate (Pi) accelerates relaxation. An interpretation these effects based on a scheme presented. (5) affinity for MgADP much muscles. (6) Creatine (CP) induced flash photolysis Diazo-2 isometrically contracted, permeabilized We suggest that this effect due removal CP creatine endogenous absence slows (7) It suggested cooperative reattachment nonphosphorylated cross-bridges, through action attached bridges maintenance force-bearing AM’.ADP states contribute high force, low phosphorylation, shortening velocity state referred as “latch.” (8) further related presence isoforms containing largely more basic LC17b lacking 7-amino-acid insert head region.