title: The role of Ca2+ in cross-bridge kinetics in chemically skinned rabbit psoas fibers.
abstract: The sinusoidal analysis method is applied to chemically skinned rabbit psoas preparations, and the effect of Ca ions on exponential processes is determined. The results are compared to the predictions of two classes of models, those in which the binding of Ca2+ to the thin filaments acts as a switch to fully activate a segment of the filament (switch hypothesis), and those in which the binding of Ca2+ results in a graded increase in activity in proportion to the fraction of sites occupied (graded hypothesis). Although qualitative features of our results are in accord with the switch hypothesis, quantitative examination of the results shows that there is an extra process (B'), which produces a W-shaped phase-frequency plot during partial activation. This result is consistent with the assumption that there are two activated states available to the thin filaments of structured muscle.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003285:Contractile Proteins / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*
chemical_list: D003285:Contractile Proteins; D000251:Adenosine Triphosphatases; D002118:Calcium