Regulation of Ca(2+)-dependent ATPase activity in detergent-skinned vascular smooth muscle.
We measured force, actin-activated myosin adenosinetriphosphatase (ATPase) activity, and myosin light-chain (MLC) phosphorylation levels in Triton X-100 detergent-skinned media of swine carotid arteries. Pseudo-ATPase activity composed of MLC kinase and phosphatase activities contributed maximally 12% to steady-state tissue ATPase activity. An increase in the Ca2+ concentration ([Ca2+]) induced an increase in force, MLC phosphorylation, and actin-activated myosin ATPase activity; this protocol was defined as the force development phase of contraction. Force maintenance was defined as the state induced by decreasing the [Ca2+] after a maximal contraction. Lowering the [Ca2+] decreased MLC phosphorylation to levels similar to those measured during force development at each [Ca2+]. In contrast, force remained at elevated levels while actin-activated myosin ATPase activity fell to significantly lower levels than those measured during the development phase for each [Ca2+]. We suggest that the significantly lower actin-activated myosin ATPase activity observed during a state of elevated force, compared with the development phase of a contraction, is evidence of slowly cycling latch bridges.
Zhang
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Bockus Research Institute, Graduate Hospital, Philadelphia, Pennsylvania 19146.
Moreland
R S
RS
D000199:Actins / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D006652:Histological Techniques; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*; D009218:Myosins / Q000737:chemistry / Q000378:metabolism; D017830:Octoxynol; D009994:Osmolar Concentration; D010766:Phosphorylation; D013552:Swine; D014661:Vasoconstriction / Q000502:physiology
D000199:Actins; D017830:Octoxynol; D009218:Myosins; D000252:Calcium-Transporting ATPases; D002118:Calcium