Thin-filament regulation of force redevelopment kinetics in rabbit skeletal muscle fibres
Thin-filament regulation of force redevelopment kinetics in rabbit skeletal muscle fibres
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DOI：
10.1113/jphysiol.2006.124164
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发表时间：
2007-03-01
影响因子：
5.5
通讯作者：
Regnier, Michael
中科院分区：
文献类型：
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作者：
Moreno-Gonzalez, Alicia;Gillis, Todd E.;Regnier, Michael
用心肌肌钙蛋白C（cTnC）、I位点失活的骨骼肌肌钙蛋白C突变体（xsTnC）或纯化的骨骼肌肌钙蛋白C（sTnC）和I、II位点失活的骨骼肌肌钙蛋白C突变体（xxsTnC）的混合物替代天然肌钙蛋白C，在兔腰肌纤维中研究了等长收缩力重建（k（tr））的细丝调节。随着sTnC：xxsTnC混合物中sTnC分数的降低，重构的最大Ca 2+激活力（rF（max））降低，但最大k（tr）不受影响，直到rF（max）<提取前F-max的0.2。相比之下，用cTnC或xsTnC重建使最大k（tr）分别降低至对照的0.48和0.44（P < 0.01），相应的rF（max）为0.68 +/- 0.03和0.25 +/- 0.02 F-max。含有sTnC：xxsTnC混合物（rF（max）> 0. 2F-max）的纤维的k（tr）-pCa关系几乎不受影响，尽管在低Ca ~（2+）活化下k（tr）略有升高。cTnC或xsTnC重建后，k（tr）的Ca 2+依赖性增加幅度大大降低，因为低水平Ca 2+时k（tr）升高，最大k（tr）降低。含有sTnC（26 +/- 0.1 s（-1））、cTnC（38 +/- 0.9 s（-1））和xsTnC（50 +/- 1.2 s（-1））的完整Tn复合物的溶液Ca 2+解离速率（k（off））与低Ca 2+水平下的k（tr）相关，与rF（max）呈负相关。在低Ca 2+激活，k（tr）类似地升高cTnC重建的纤维与ATP或当跨桥循环速率增加与2-脱氧-ATP。我们的研究结果和模型模拟表明，很少或没有要求之间的合作相互作用的细丝调节单位在任何[Ca 2 +]调节k（tr），并建议Ca 2+激活个别肌钙蛋白复合物的性质可能会影响跨桥分离的表观速率常数。
Thin-filament regulation of isometric force redevelopment (k(tr)) was examined in rabbit psoas fibres by substituting native TnC with either cardiac TnC (cTnC), a site I-inactive skeletal TnC mutant (xsTnC), or mixtures of native purified skeletal TnC (sTnC) and a site I- and II-inactive skeletal TnC mutant (xxsTnC). Reconstituted maximal Ca2+-activated force (rF(max)) decreased as the fraction of sTnC in sTnC: xxsTnC mixtures was reduced, but maximal k(tr) was unaffected until rF(max) was < 0.2 of pre-extracted F-max. In contrast, reconstitution with cTnC or xsTnC reduced maximal k(tr) to 0.48 and 0.44 of control (P < 0.01), respectively, with corresponding rF(max) of 0.68 +/- 0.03 and 0.25 +/- 0.02 F-max. The k(tr)-pCa relation of fibres containing sTnC: xxsTnC mixtures (rF(max) > 0.2 F-max) was little effected, though k(tr) was slightly elevated at low Ca2+ activation. The magnitude of the Ca2+-dependent increase in k(tr) was greatly reduced following cTnC or xsTnC reconstitution because k(tr) at low levels of Ca2+ was elevated and maximal k(tr) was reduced. Solution Ca2+ dissociation rates (k(off)) from whole Tn complexes containing sTnC (26 +/- 0.1 s(-1)), cTnC (38 +/- 0.9 s(-1)) and xsTnC (50 +/- 1.2 s(-1)) correlated with k(tr) at low Ca2+ levels and were inversely related to rF(max). At low Ca2+ activation, k(tr) was similarly elevated in cTnC-reconstituted fibres with ATP or when cross-bridge cycling rate was increased with 2-deoxy-ATP. Our results and model simulations indicate little or no requirement for cooperative interactions between thin-filament regulatory units in modulating k(tr) at any [Ca2+] and suggest Ca2+ activation properties of individual troponin complexes may influence the apparent rate constant of cross-bridge detachment.