Article

Effects of calcium, inorganic phosphate, and pH on isometric force in single skinned cardiomyocytes from donor and failing human hearts.

Laboratory for Physiology, Department of Cardiology, Institute for Cardiovascular Research, Free University, Amsterdam, the Netherlands.
Circulation (Impact Factor: 15.2). 10/2001; 104(10):1140-6.
Source: PubMed

ABSTRACT 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.

0 Bookmarks
 · 
53 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Despite major improvements in the treatment of virtually all cardiac disorders, heart failure (HF) is an exception, in that its prevalence is rising, and only small prolongations in survival are occurring. An increasing fraction, especially older women with diabetes, obesity, and atrial fibrillation exhibit HF with preserved systolic function. Several pathogenetic mechanisms appear to be operative in HF. These include increased hemodynamic overload, ischemia-related dysfunction, ventricular remodeling, excessive neurohumoral stimulation, abnormal myocyte calcium cycling, excessive or inadequate proliferation of the extracellular matrix, accelerated apoptosis, and genetic mutations. Biomarkers released as a consequence of myocardial stretch, imbalance between formation and breakdown of extracellular matrix, inflammation, and renal failure are useful in the identification of the pathogenetic mechanism and, when used in combination, may become helpful in estimating prognosis and selecting appropriate therapy. Promising new therapies that are now undergoing intensive investigation include an angiotensin receptor neprilysin inhibitor, a naturally-occurring vasodilator peptide, a myofilament sensitizer and several drugs that enhance Ca(++) uptake by the sarcoplasmic reticulum. Cell therapy, using autologous bone marrow and cardiac progenitor cells, appears to be promising, as does gene therapy. Chronic left ventricular assistance with continuous flow pumps is being applied more frequently and successfully as destination therapy, as a bridge to transplantation, and even as a bridge to recovery and explantation. While many of these therapies will improve the care of patients with HF, significant reductions in prevalence will require vigorous, multifaceted, preventive approaches.
    JACC. Heart failure. 02/2013; 1(1):1-20.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Heart failure is associated with pump dysfunction and remodeling but it is not yet known if the condition affects different transmural regions of the heart in the same way. We tested the hypotheses that the left ventricles of non-failing human hearts exhibit transmural heterogeneity of cellular level contractile properties, and that heart failure produces transmural region-specific changes in contractile function. Permeabilized samples were prepared from the sub-epicardial, mid-myocardial, and sub-endocardial regions of the left ventricular free wall of non-failing (n = 6) and failing (n = 10) human hearts. Power, an in vitro index of systolic function, was higher in non-failing mid-myocardial samples (0.59±0.06 μW mg- 1) than in samples from the sub-epicardium (p = 0.021) and the sub-endocardium (p = 0.015). Non-failing mid-myocardial samples also produced more isometric force (14.3±1.33 kN m- 2) than samples from the sub-epicardium (p = 0.008) and the sub-endocardium (p = 0.026). Heart failure reduced power (p = 0.009) and force (p = 0.042) but affected the mid-myocardium more than the other transmural regions. Fibrosis increased with heart failure (p = 0.021) and mid-myocardial tissue from failing hearts contained more collagen than matched sub-epicardial (p < 0.001) and sub-endocardial (p = 0.043) samples. Power output was correlated with the relative content of actin and troponin I, and was also statistically linked to the relative content and phosphorylation of desmin and myosin light chain- 1. Non-failing human hearts exhibit transmural heterogeneity of contractile properties. In failing organs, region-specific fibrosis produces the greatest contractile deficits in the mid-myocardium. Targeting fibrosis and sarcomeric proteins in the mid-myocardium may be particularly effective therapies for heart failure.
    Journal of Molecular and Cellular Cardiology 01/2014; · 5.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Understanding how cardiac myosin RLC phosphorylation alters cardiac muscle mechanics is important as it is often altered in cardiac disease. However the effect this protein phosphorylation has on muscle mechanics during physiological shortening has not been addressed. We have expressed and phosphorylated recombinant Rattus Norvegicus left ventricular RLC. In-vitro we have phosphorylated these recombinant species with cardiac myosin light chain kinase (cMLCK) and zipper interacting protein kinase (ZIPK). We compare skinned cardiac trabeculae of the rat, which have undergone exchange with differently phosphorylated RLC species. We were able to enrich trabecular RLC phosphorylation by 40% compared to controls and, in a separate series, lower RLC phosphorylation to 60% of control values. Compared to the trabeculae with a low level RLC phosphorylation, RLC phosphorylation enrichment increased isometric force by more than 3-fold, peak power output by more than seven-fold and approximately doubled both maximum shortening speed and the shortening velocity that generated peak power. We augmented these measurements by observing increased RLC phosphorylation by Phos-TagTM SDS-PAGE analysis of human and rat HF samples from endocardial left ventricular homogenate. These results demonstrate the importance of increased RLC phosphorylation in the upregulation of myocardial performance, and suggest that reduced RLC phosphorylation is a key aspect of impaired contractile function in the diseased myocardium.
    Journal of Biological Chemistry 03/2013; · 4.65 Impact Factor

Full-text (2 Sources)

View
8 Downloads
Available from
May 17, 2014