Effect of ionic strength on skinned rabbit psoas fibers in the presence of magnesium pyrophosphate.
The effect of ionic strength on the kinetics of myosin cross-bridges in the presence of the ATP analogue PP, has been examined. It was found that increasing ionic strength from moderate values (mu approximately 100 mM) to high values (mu approximately 200 mM) has three effects. It causes a big decrease in the half time for the force decay after a small stretch, it causes a significant decrease in the sigmoidicity of the nucleotide analogue concentration dependence of the "apparent rate constant" of force decay after a small stretch, and it causes a big decrease in the range of rate constants necessary to describe the multiexponential force decay. It causes the last of these by causing a much larger increase in the slowest rate constants of the decay than in the fastest rate constants. The results suggest that whereas the behavior of cross-bridges in the presence of ATP is well-described by the simple independent-head equilibrium cross-bridge model of Schoenberg (1985. Biophys. J. 48:467-475), cross-bridges in the presence of the ATP analogue PPi require the more complicated double-headed equilibrium cross-bridge model of Anderson and Schoenberg (1987. Biophys. J. 52: 1077-1082) to describe their behavior.
Schoenberg
M
M
Laboratory of Physical Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland 20892.
D000818:Animals; D011756:Diphosphates / Q000494:pharmacology*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D017616:Magnesium Compounds; D008954:Models, Biological; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D009994:Osmolar Concentration; D011817:Rabbits
D011756:Diphosphates; D017616:Magnesium Compounds; C034732:magnesium pyrophosphate; D008274:Magnesium