Isometric force redevelopment of skinned muscle fibers from rabbit activated with and without Ca2+. |
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Authors: | P B Chase D A Martyn and J D Hannon |
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Institution: | Department of Radiology, University of Washington, Seattle 98195. |
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Abstract: | Fiber isometric tension redevelopment rate (kTR) was measured during submaximal and maximal activations in glycerinated fibers from rabbit psoas muscle. In fibers either containing endogenous skeletal troponin C (sTnC) or reconstituted with either purified cardiac troponin C (cTnC) or sTnC, graded activation was achieved by varying Ca2+]. Some fibers were first partially, then fully, reconstituted with a modified form of cTnC (aTnC) that enables active force generation and shortening in the absence of Ca2+. kTR was derived from the half-time of tension redevelopment. In control fibers with endogenous sTnC, kTR increased nonlinearly with Ca2+], and maximal kTR was 15.3 +/- 3.6 s-1 (mean +/- SD; n = 26 determinations on 25 fibers) at pCa 4.0. During submaximal activations by Ca2+, kTR in cTnC reconstituted fibers was approximately threefold faster than control, despite the lower (60%) maximum Ca(2+)-activated force after reconstitution. To obtain submaximal force with aTnC, eight fibers were treated to fully extract endogenous sTnC, then reconstituted with a mixture of a TnC and cTnC (aTnC:cTnC molar ratio 1:8.5). A second extraction selectively removed cTnC. In such fibers containing aTnC only, neither force nor kTR was affected by changes in Ca2+]. Force was 22 +/- 7% of maximum control (mean +/- SD; n = 15) at pCa 9.2 vs. 24 +/- 8% (mean +/- SD; n = 8) at pCa 4.0, whereas kTR was 98 +/- 14% of maximum control (mean +/- SD; n = 15) at pCa 9.2 vs. 96 +/- 15% (mean +/- SD; n = 8) at pCa 4.0.(ABSTRACT TRUNCATED AT 250 WORDS) |
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