Cross-bridge cycling regulation

Figure 22.12 Regulation of actin-myosin interaction in smooth muscle via the light-chain kinase and phosphatase and effect on blood pressure. ions bind to calmodulin and the complex stimulates the conversion of inactive myosin light chain kinase (MLCK) to active MLCK which then phosphorylates the light chain. This results in activation of the cross-bridge cycle. The overall effect is vasoconstriction of the arteriole, which increases blood pressure.

By using caged compounds in combination with permeabilized smooth muscle preparations, valuable information regarding the rate-limiting steps between excitation and contraction (see Somlyo and Somlyo, 1990, for review Somlyo et al., 1992), regulation of Ca + release from the SR (Walker et al., 1987 lino and Endo, 1992), and the kinetics of the cross-bridge cycle (Arner et al., 1987 Somlyo et al, 1988 Fuglsang et al,... 

Regulation of Cross-bridge Cycling in Smooth Muscle... 

IV. POTENTIAL SITES OF REGULATION IN THE CROSS-BRIDGE CYCLE... 

Regulation by myosin phosphorylation, which is of particular importance for smooth muscle, is a feature of the less specialized actomyosin contractile systems. In striated muscle it would appear that light chain phosphorylation has been relegated to a modulatory role in the cross-bridge cycle, and response to stimulation has been accelerated by the evolution of the troponin system located in the I filament. The consequence is that the rapid binding of calcium to one molecule of troponin C renders seven actin molecules available to interact with as many heads of myosin molecules as they can accommodate. In smooth muscle, binding of cal-... 

Regulation of cross-bridge cycling by Ca in smooth muscle... 

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