Metzger J M, Parmacek M S, Barr E, Pasyk K, Lin W I, Cochrane K L, Field L J, Leiden J M
Department of Physiology, University of Michigan, School of Medicine, Ann Arbor 48109.
Proc Natl Acad Sci U S A. 1993 Oct 1;90(19):9036-40. doi: 10.1073/pnas.90.19.9036.
Depressed contractile function plays a primary role in the pathophysiology of acute myocardial ischemia. Intracellular acidification is an important factor underlying the inhibition of force production in the ischemic myocardium. The effect of acidosis to depress contractility is markedly greater in cardiac as compared to skeletal muscle; however, the molecular basis of this difference in sensitivity to acidosis is not clearly understood. In this report, we describe transgenic mice that express the fast skeletal isoform of troponin C (sTnC) in cardiac muscle. In permeabilized single cardiac myocytes the shift in the midpoint of the tension-pCa relationship (i.e., pCa50, where pCa is -log[Ca2+]) due to lowering pH from 7.00 to 6.20 was 1.27 +/- 0.03 (n = 7) pCa units in control cardiac TnC (cTnC) expressing myocytes and 0.96 +/- 0.04 (n = 11) pCa unit in transgenic cardiac myocytes (P < 0.001). The effect of pH to alter maximum Ca(2+)-activated tension was unchanged by TnC isoforms in these cardiac myocytes. In a reciprocal experiment, contractile sensitivity to acidosis was increased in fast skeletal muscle fibers following extraction of endogenous sTnC and reconstitution with purified cTnC in vitro. Our findings demonstrate that TnC plays an important role in determining the profound sensitivity of cardiac muscle to acidosis and identify cTnC as a target for therapeutic interventions designed to modify ischemia-induced myocardial contractile dysfunction.
收缩功能降低在急性心肌缺血的病理生理学中起主要作用。细胞内酸化是缺血心肌中抑制力产生的一个重要因素。与骨骼肌相比，酸中毒对心脏收缩力的抑制作用明显更大；然而，这种对酸中毒敏感性差异的分子基础尚不清楚。在本报告中，我们描述了在心肌中表达肌钙蛋白C快速骨骼肌亚型（sTnC）的转基因小鼠。在通透的单个心肌细胞中，由于pH从7.00降至6.20，对照心肌肌钙蛋白C（cTnC）表达的心肌细胞中张力-pCa关系中点（即pCa50，其中pCa为-log[Ca2+]）的变化为1.27±0.03（n = 7）个pCa单位，而转基因心肌细胞中为0.96±0.04（n = 11）个pCa单位（P < 0.001）。在这些心肌细胞中，pH改变最大Ca2+激活张力的作用不受TnC亚型的影响。在一项反向实验中，在体外提取内源性sTnC并用纯化的cTnC重构后，快速骨骼肌纤维对酸中毒的收缩敏感性增加。我们的研究结果表明，TnC在决定心肌对酸中毒的高度敏感性方面起重要作用，并确定cTnC为旨在改善缺血诱导的心肌收缩功能障碍的治疗干预靶点。
