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

Erasmus University Rotterdam, Rotterdam, South Holland, Netherlands
Circulation (Impact Factor: 14.43). 10/2001; 104(10):1140-6. DOI: 10.1161/hc3501.095485
Source: PubMed


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.

Download full-text


Available from: Lucas J Klein
    • "Force measurements in single-myocyte-sized preparations A permeabilized single cardiomyocyte was mounted between two thin needles with silicone adhesive (DAP Aquarium, Baltimore, USA) while viewed under an inverted microscope (Axiovert 135, Zeiss, Germany).[34] [35] One needle was attached to a force transducer element (SensoNor, Horten, Norway) and the other to an electromagnetic motor (Aurora Scientific Inc., Aurora, Canada). The measurements were performed at 15°C and the average sarcomere length was adjusted to 2.3 mm as described previously [36]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Intracellular free heme predisposes to oxidant-mediated tissue damage. We hypothesized that free heme causes alterations in myocardial contractility via disturbed structure and/or regulation of the contractile proteins. Isometric force production and its Ca(2+)-sensitivity (pCa50) were monitored in permeabilized human ventricular cardiomyocytes. Heme exposure altered cardiomyocyte morphology and evoked robust decreases in Ca(2+)-activated maximal active force (Fo) while increasing Ca(2+)-independent passive force (Fpassive). Heme treatments, either alone or in combination with H2O2, did not affect pCa50. The increase in Fpassive started at 3µM heme exposure and could be partially reversed by the antioxidant dithiothreitol. Protein sulfhydryl (SH) groups of thick myofilament content decreased and sulfenic acid formation increased after treatment with heme. Partial restoration in the SH group content was observed in a protein running at 140kDa after treatment with dithiothreitol, but not in other proteins, such as filamin C, myosin heavy chain, cardiac myosin binding protein C, and α-actinin. Importantly, binding of heme to hemopexin or alpha-1-microglobulin prevented its effects on cardiomyocyte contractility, suggesting an allosteric effect. In line with this, free heme directly bound to myosin light chain 1 in human cardiomyocytes. Our observations suggest that free heme modifies cardiac contractile proteins via posttranslational protein modifications and via binding to myosin light chain 1, leading to severe contractile dysfunction. This may contribute to systolic and diastolic cardiac dysfunctions in hemolytic diseases, heart failure, and myocardial ischemia-reperfusion injury.
    No preview · Article · Sep 2015 · Free Radical Biology and Medicine
  • Source
    • "Force measurements were performed in single, mechanically isolated cardiomyocytes as described previously [18]. Briefly, LV samples (frozen after saline injection) were defrosted in relaxing solution (free Mg 1, KCl 100, EGTA 2, Mg-ATP 4 and imidazole 10 mmol/L; pH 7.0), mechanically disrupted and incubated for 5 minutes in relaxing solution supplemented with 0.5% Triton X-100 to remove all membrane structures. "
    [Show abstract] [Hide abstract]
    ABSTRACT: In vitro data suggest that changes in myocardial substrate metabolism may contribute to impaired myocardial function in diabetic cardiomyopathy (DCM). The purpose of the present study was to study in a rat model of early DCM, in vivo changes in myocardial substrate metabolism and their association with myocardial function. Zucker diabetic fatty (ZDF) and Zucker lean (ZL) rats underwent echocardiography followed by [11C]palmitate positron emission tomography (PET) under fasting, and [18F]-2-fluoro-2-deoxy-D-glucose PET under hyperinsulinaemic euglycaemic clamp conditions. Isolated cardiomyocytes were used to determine isometric force development. PET data showed a 66% decrease in insulin-mediated myocardial glucose utilisation and a 41% increase in fatty acid (FA) oxidation in ZDF vs. ZL rats (both p < 0.05). Echocardiography showed diastolic and systolic dysfunction in ZDF vs. ZL rats, which was paralleled by a significantly decreased maximal force (68%) and maximal rate of force redevelopment (69%) of single cardiomyocytes. Myocardial functional changes were significantly associated with whole-body insulin sensitivity and decreased myocardial glucose utilisation. ZDF hearts showed a 68% decrease in glucose transporter-4 mRNA expression (p < 0.05), a 22% decrease in glucose transporter-4 protein expression (p = 0.10), unchanged levels of pyruvate dehydrogenase kinase-4 protein expression, a 57% decreased phosphorylation of AMP activated protein kinase alpha1/2 (p < 0.05) and a 2.4-fold increased abundance of the FA transporter CD36 to the sarcolemma (p < 0.01) vs. ZL hearts, which are compatible with changes in substrate metabolism. In ZDF vs. ZL hearts a 2.4-fold reduced insulin-mediated phosphorylation of Akt was found (p < 0.05). Using PET and echocardiography, we found increases in myocardial FA oxidation with a concomitant decrease of insulin-mediated myocardial glucose utilisation in early DCM. In addition, the latter was associated with impaired myocardial function. These in vivo data expand previous in vitro findings showing that early alterations in myocardial substrate metabolism contribute to myocardial dysfunction.
    Full-text · Article · Feb 2009 · Cardiovascular Diabetology
  • Source
    • "However, myofilament Ca 2+ sensitivity in cardiomyocytes from patients with less severe forms of cardiomyopathy (NYHA class II/III) was similar to that in donor cardiomyocytes. This supports the notion that the increased Ca 2+ -sensitivity is a hallmark of endstage failing human hearts [36]. Recently, similar observations were obtained in a rat model of right ventricular heart failure resulting from pressure overload [37] [38], in which the increased myofilament Ca 2+ -sensitivity in failing cardiomyocytes was decreased to values observed in healthy rat cardiomyocytes upon PKA treatment [38]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: In human heart failure beta-adrenergic-mediated protein kinase A (PKA) activity is down-regulated, while protein kinase C (PKC) activity is up-regulated. PKC-mediated myofilament protein phosphorylation might be detrimental for contractile function in cardiomyopathy. This study was designed to reveal the effects of PKC on myofilament function in human myocardium under basal conditions and upon modulation of protein phosphorylation by PKA and phosphatases. Isometric force was measured at different [Ca(2+)] in single permeabilized cardiomyocytes from non-failing and failing human left ventricular tissue. Basal phosphorylation of myofilament proteins and the influence of PKC, PKA, and phosphatase treatments were analyzed by one- and two-dimensional gel electrophoresis, Western immunoblotting, and ELISA. Troponin I (TnI) phosphorylation at the PKA sites was decreased in failing compared to non-failing hearts and correlated well with myofilament Ca(2+) sensitivity (pCa(50)). Incubation with the catalytic domain of PKC slightly decreased maximal force under basal conditions, but not following PKA and phosphatase pretreatments. PKC reduced Ca(2+) sensitivity to a larger extent in failing (DeltapCa(50)=0.19+/-0.03) than in non-failing (DeltapCa(50)=0.08+/-0.01) cardiomyocytes. This shift was reduced, though still significant, when PKC was preceded by PKA, while PKA following PKC did not further decrease pCa(50). Protein analysis indicated that PKC phosphorylated PKA sites in human TnI and increased phosphorylation of troponin T, while myosin light chain phosphorylation remained unaltered. In human myocardium PKC-mediated myofilament protein phosphorylation only has a minor effect on maximal force development. The PKC-mediated decrease in Ca(2+) sensitivity may serve to improve diastolic function in failing human myocardium in which PKA-mediated TnI phosphorylation is decreased.
    Full-text · Article · Apr 2006 · Cardiovascular Research
Show more