Gollapudi Sampath K, Chandra Murali
Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology (VCAPP), Washington State University, Pullman, WA 99164-6520, USA.
Biochem Res Int. 2012;2012:824068. doi: 10.1155/2012/824068. Epub 2012 Sep 12.
Previous studies of cardiomyopathy-related mutations in cardiac troponin C (cTnC)-L29Q and G159D-have shown diverse findings. The link between such mutant effects and their divergent impact on cardiac phenotypes has remained elusive due to lack of studies on contractile dynamics. We hypothesized that a cTnC mutant-induced change in the thin filament will affect global myofilament mechanodynamics because of the interactions of thin filament kinetics with both Ca(2+) binding and crossbridge (XB) cycling kinetics. We measured pCa-tension relationship and contractile dynamics in detergent-skinned rat cardiac papillary muscle fibers reconstituted with the recombinant wild-type rat cTnC (cTnC(WT)), cTnC(L29Q), and cTnC(G159D) mutants. cTnC(L29Q) fibers demonstrated a significant decrease in Ca(2+) sensitivity, but cTnC(G159D) fibers did not. Both mutants had no effect on Ca(2+)-activated maximal tension. The rate of XB recruitment dynamics increased in cTnC(L29Q) (26%) and cTnC(G159D) (25%) fibers. The rate of XB distortion dynamics increased in cTnC(G159D) fibers (15%). Thus, the cTnC(L29Q) mutant modulates the equilibrium between the non-cycling and cycling pool of XB by affecting the on/off kinetics of the regulatory units (Tropomyosin-Troponin); whereas, the cTnC(G159D) mutant increases XB cycling rate. Different effects on contractile dynamics may offer clue regarding how cTnC(L29Q) and cTnC(G159D) cause divergent effects on cardiac phenotypes.
先前关于心肌肌钙蛋白C（cTnC）-L29Q和G159D心肌病相关突变的研究结果不一。由于缺乏对收缩动力学的研究，此类突变效应与其对心脏表型的不同影响之间的联系仍不明确。我们推测，cTnC突变引起的细肌丝变化会影响整体肌丝力学动力学，因为细肌丝动力学与Ca(2+)结合及横桥（XB）循环动力学相互作用。我们测量了用重组野生型大鼠cTnC（cTnC(WT)）、cTnC(L29Q)和cTnC(G159D)突变体重构的去垢剂处理的大鼠心脏乳头肌纤维中的pCa-张力关系和收缩动力学。cTnC(L29Q)纤维的Ca(2+)敏感性显著降低，但cTnC(G159D)纤维没有。两种突变体对Ca(2+)激活的最大张力均无影响。cTnC(L29Q)（26%）和cTnC(G159D)（25%）纤维中XB募集动力学速率增加。cTnC(G159D)纤维中XB变形动力学速率增加（15%）。因此，cTnC(L29Q)突变体通过影响调节单位（原肌球蛋白-肌钙蛋白）的开启/关闭动力学来调节XB非循环池和循环池之间的平衡；而cTnC(G159D)突变体增加XB循环速率。对收缩动力学的不同影响可能为cTnC(L29Q)和cTnC(G159D)如何对心脏表型产生不同影响提供线索。
