Effects of Calcium, Inorganic Phosphate, and pH on Isometric Force in Single Skinned Cardiomyocytes From Donor and Failing Human Hearts

Abstract

Background-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 2ϩ , P i , and pH. Methods and Results-Isometric force was studied in mechanically isolated Triton-skinned single myocytes from left ventricular myocardium. Force declined with added P i to 0.33Ϯ0.02 of the control force (pH 7.1, 0 mmol/L P i ) at 30 mmol/L P i and increased with pH from 0.64Ϯ0.03 at pH 6.2 to 1.27Ϯ0.02 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 2ϩ ]. Ca 2ϩ 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 2ϩ responsiveness of force and myosin light chain 2 phosphorylation. Conclusions-Our results indicate that contractile protein alterations in human end-stage heart failure alter Ca

Transmural Heterogeneity of Cellular Level Power Output Is Reduced in Human Heart Failure

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Altered Titin Expression, Myocardial Stiffness, and Left Ventricular Function in Patients With Dilated Cardiomyopathy

“…We have previously shown that this results in excellent tissue preservation (Figure 5B in Freiburg et al), 19 whereas others 3,21 have shown that active and passive mechanical properties are well maintained in freeze-thawed samples. Muscle strips were dissected from LV specimens, skinned overnight at 4°C in relaxing solution containing 1% vol/vol Triton X-100, and then washed thoroughly with relaxing solution.…”

Altered myocardial force generation in end‐stage human heart failure

“…The elimination of the higher Ca 2+ sensitivity of force production by 10 mM P i in the failing myocytes occurred both at pH 7.2 and at pH 6.5, in perfect agreement with the notion that the P i effect is independent from that of protons. 24,27 …”

“…27 During physiological cardiac activity, the thin filaments are far from Ca 2+ saturation. Differences in the mechanical parameters of failing and non-failing hearts at intermediate [Ca 2+ ] therefore bear important functional consequences for the cardiac performance.…”