van Der Velden J, Klein L J, Zaremba R, Boontje N M, Huybregts M A, Stooker W, Eijsman L, de Jong J W, Visser C A, Visser F C, Stienen G J
Laboratory for Physiology, Department of Cardiology, Institute for Cardiovascular Research, Free University, Amsterdam, the Netherlands.
Circulation. 2001 Sep 4;104(10):1140-6. doi: 10.1161/hc3501.095485.
During ischemia, the intracellular calcium and inorganic phosphate (P(i)) concentrations rise and pH falls. We investigated the effects of these changes on force development in donor and failing human hearts to determine if altered contractile protein composition during heart failure changes the myocardial response to Ca(2+), P(i), and pH.
Isometric force was studied in mechanically isolated Triton-skinned single myocytes from left ventricular myocardium. Force declined with added P(i) to 0.33+/-0.02 of the control force (pH 7.1, 0 mmol/L P(i)) at 30 mmol/L P(i) and increased with pH from 0.64+/-0.03 at pH 6.2 to 1.27+/-0.02 at pH 7.4. Force dependency on P(i) and pH did not differ between donor and failing hearts. Incubation of myocytes in a P(i)-containing activating solution caused a potentiation of force, which was larger at submaximal than at maximal [Ca(2+)]. Ca(2+) sensitivity of force was similar in donor hearts and hearts with moderate cardiac disease, but in end-stage failing myocardium it was significantly increased. The degree of myosin light chain 2 phosphorylation was significantly decreased in end-stage failing compared with donor myocardium, resulting in an inverse correlation between Ca(2+) responsiveness of force and myosin light chain 2 phosphorylation.
Our results indicate that contractile protein alterations in human end-stage heart failure alter Ca(2+) responsiveness of force but do not affect the force-generating capacity of the cross-bridges or its P(i) and pH dependence. In end-stage failing myocardium, the reduction in force by changes in pH and [P(i)] at submaximal [Ca(2+)] may even be less than in donor hearts because of the increased Ca(2+) responsiveness.
在缺血期间，细胞内钙和无机磷酸盐（P(i)）浓度升高而pH值下降。我们研究了这些变化对供体和衰竭人类心脏中力产生的影响，以确定心力衰竭期间收缩蛋白组成的改变是否会改变心肌对Ca(2+)、P(i)和pH的反应。
在机械分离的来自左心室心肌的经曲拉通处理的单个肌细胞中研究等长力。在30 mmol/L P(i)时，随着P(i)添加，力下降至对照力（pH 7.1，0 mmol/L P(i)）的0.33±0.02，并且随着pH从pH 6.2时的0.64±0.03增加至pH 7.4时的1.27±0.02。供体心脏和衰竭心脏之间力对P(i)和pH的依赖性没有差异。将肌细胞在含P(i)的激活溶液中孵育会导致力增强，在次最大[Ca(2+)]时比最大[Ca(2+)]时更大。供体心脏和中度心脏病心脏中力的Ca(2+)敏感性相似，但在终末期衰竭心肌中显著增加。与供体心肌相比，终末期衰竭心肌中肌球蛋白轻链2磷酸化程度显著降低，导致力的Ca(2+)反应性与肌球蛋白轻链2磷酸化之间呈负相关。
我们的结果表明，人类终末期心力衰竭中收缩蛋白的改变会改变力的Ca(2+)反应性，但不影响横桥的力产生能力或其对P(i)和pH的依赖性。在终末期衰竭心肌中，由于Ca(2+)反应性增加，在次最大[Ca(2+)]时pH和[P(i)]变化导致的力降低甚至可能小于供体心脏。
