Metabolic consequences of a species difference in Gibbs free energy of Na/Ca exchange: rat versus guinea pig
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چکیده
Cooper, P. J., M.-L. Ward, P. J. Hanley, G. R. Denyer, and D. S. Loiselle. Metabolic consequences of a species difference in Gibbs free energy of Na/Ca exchange: rat versus guinea pig. Am J Physiol Regulatory Integrative Comp Physiol 280: R1221–R1229, 2001.—The Gibbs free energy of the sarcolemmal Na/Ca exchanger (DGNa/Ca) determines its net Ca flux. We tested the hypothesis that a difference of diastolic DGNa/Ca exists between rat and guinea pig myocardium. We measured the suprabasal rate of oxygen consumption (VO2) of arrested Langendorff-perfused hearts of both species, manipulating DGNa/Ca by reduction of extracellular Na concentration, [Na]o. Hill equations fitted to the resulting VO2-[Na ]o relationships yielded Michaelis constant (Km) values of 67 and 25 mM for rat and guinea pig, respectively. We developed and tested a simple thermodynamic model that attributes this difference of Km values to a 7.84 kJ/mol difference of DGNa/Ca. The model predicts that reversal of Na/Ca exchange, leading to diastolic Ca influx, should occur at a value of [Na]o about three times higher in rat myocardium. We verified this quantitative prediction using fura 2 fluorescence to index intracellular Ca concentration in isolated ventricular trabeculae at 37°C. The postulated difference in free energy of Na/Ca exchange explains a number of reported disparities of Ca handling at rest between rat and guinea pig myocardia.
منابع مشابه
Metabolic consequences of a species difference in Gibbs free energy of Na+/Ca2+ exchange: rat versus guinea pig.
The Gibbs free energy of the sarcolemmal Na+/Ca2+ exchanger (DeltaG(Na/Ca)) determines its net Ca2+ flux. We tested the hypothesis that a difference of diastolic DeltaG(Na/Ca) exists between rat and guinea pig myocardium. We measured the suprabasal rate of oxygen consumption (VO2) of arrested Langendorff-perfused hearts of both species, manipulating DeltaG(Na/Ca) by reduction of extracellular N...
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