title: Electrophysiological Determination of Submembrane Na(+) Concentration in Cardiac Myocytes.
abstract: In the heart, Na(+) is a key modulator of the action potential, Ca(2+) homeostasis, energetics, and contractility. Because Na(+) currents and cotransport fluxes depend on the Na(+) concentration in the submembrane region, it is necessary to accurately estimate the submembrane Na(+) concentration ([Na(+)]sm). Current methods using Na(+)-sensitive fluorescent indicators or Na(+) -sensitive electrodes cannot measure [Na(+)]sm. However, electrophysiology methods are ideal for measuring [Na(+)]sm. In this article, we develop patch-clamp protocols and experimental conditions to determine the upper bound of [Na(+)]sm at the peak of action potential and its lower bound at the resting state. During the cardiac cycle, the value of [Na(+)]sm is constrained within these bounds. We conducted experiments in rabbit ventricular myocytes at body temperature and found that 1) at a low pacing frequency of 0.5 Hz, the upper and lower bounds converge at 9 mM, constraining the [Na(+)]sm value to ∼9 mM; 2) at 2 Hz pacing frequency, [Na(+)]sm is bounded between 9 mM at resting state and 11.5 mM; and 3) the cells can maintain [Na(+)]sm to the above values, despite changes in the pipette Na(+) concentration, showing autoregulation of Na(+) in beating cardiomyocytes.
authors.affiliation: Department of Pharmacology, University of California, Davis, Davis, California.
authors.forename: Bence
authors.initials: B
authors.lastname: Hegyi
authors.affiliation: Department of Pharmacology, University of California, Davis, Davis, California; Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
authors.forename: Tamás
authors.initials: T
authors.lastname: Bányász
authors.affiliation: Department of Molecular Physiology and Biophysics, Rush University School of Medicine, Chicago, Illinois.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Shannon
authors.affiliation: Department of Pharmacology, University of California, Davis, Davis, California; Department of Biomedical Engineering, University of California, Davis, Davis, California; Department of Internal Medicine, Division of Cardiology, University of California, Davis, Davis, California.
authors.forename: Ye
authors.initials: Y
authors.lastname: Chen-Izu
authors.affiliation: Department of Pharmacology, University of California, Davis, Davis, California. Electronic address: ltizu@ucdavis.edu.
authors.forename: Leighton T
authors.initials: LT
authors.lastname: Izu
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000465:Algorithms; D000818:Animals; D002414:Cations, Monovalent / Q000378:metabolism; D002478:Cells, Cultured; D006352:Heart Ventricles / Q000378:metabolism; D042541:Intracellular Space / Q000378:metabolism; D008297:Male; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D002414:Cations, Monovalent; D012964:Sodium