Interaction between Na+ and H+ ions on Na-H exchange in sheep cardiac Purkinje fibers

Journal of Molecular and Cellular Cardiology
M L Wu, R D Vaughan-Jones

Abstract

The interaction between Na+ and H+ ions upon Na-H exchange (NHE) was examined in sheep cardiac Purkinje fibers. Acid equivalent fluxes through NHE were examined using recordings of intracellular pH and Na+ in isolated preparations measured with ion selective microelectrodes. The extent of acid-extrusion by NHE was estimated from pH(i) recovery-rate, multiplied by beta(i) (intracellular buffering power) in response to an internal acid load induced by 20 mm NH4Cl removal (nominally HCO3- free media). A mixed inhibitory effect was found of extracellular H+ on external Na+-activation of NHE (i.e. an increase, at low pH(o), in the apparent Michaelis constant for external Na+ ions [K(Nao)(0.5)] and a decrease in the maximum transport rate [V(Nao)(max)]). In addition, we confirmed that the stoichiometry of Na(o) binding is unaffected by the pH(o) (between 7.5 and 6.5), showing a Hill coefficient close to one. The interaction between Na+ and H+ ions at the internal face of the cardiac NHE was also studied. Our evidence suggests that an increase in the intracellular Na+ ion concentration ([Na+]i) inhibits acid efflux and that this inhibition can be approximated by the decrease in thermodynamic driving force caused by reducing the transm...Continue Reading

Citations

Aug 29, 2009·Molecules and Cells·Chae Young Cha, Akinori Noma
Feb 5, 2004·The Annals of Thoracic Surgery·Randy M StevensRobert D Lasley
Aug 10, 2000·Journal of the American College of Cardiology·H YokoyamaM Avkiran
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Apr 27, 2002·Journal of Neurophysiology·Claire Sheldon, John Church
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