Parallel measurements of bound calcium and force in glycerinated rabbit psoas muscle fibers.
A simple double-isotope procedure has been developed for making simultaneous measurements of bound Ca2+ and relative force in glycerinated rabbit psoas bundles containing two fibers. With this preparation it is possible to study Ca2+-troponin interactions coincident with MgATP-induced force development. Over the free [Ca2+] range 6 . 10(-8)--1.2 . 10(-5) M the bound Ca2+ varied from 0.25 to 1.65 mumol/g protein. The free [Ca2+] at half-maximal Ca2+ saturation was 2 . 10(-7) M while that a half-maximal force was 5 . 10(-7) M. Half-maximal Ca2+ saturation was associated with 20% maximal force. The force-[Ca2+] saturation curve showed a steep rise in slope at greater than half saturation. The observed relationship was consistent with a model in which multiple occupancy of troponin Ca2+-binding sites is essential for initiation of cross-bridge cycling.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005990:Glycerol / Q000494:pharmacology; D007700:Kinetics; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D011817:Rabbits; D014336:Troponin / Q000378:metabolism; D019209:Troponin C
D014336:Troponin; D019209:Troponin C; D005990:Glycerol; D002118:Calcium