Abstract
Electrogenic ion transport by the Na,K-ATPase was investigated in a model system of protein-containing membrane fragments adsorbed to a lipid bilayer. Transient Na+ currents were induced by photorelease of ATP from inactive caged ATP. This process was accompanied by a capacitance change of the membrane system. Two methods were applied to measure capacitances in the frequency range 1 to 6000 Hz. The frequency dependent capacitance increment, ΔC, was of sigmoidal shape and decreased at high frequencies. The midpoint frequency, f 0, depended on the ionic strength of the buffer. At 150 mm NaCl f 0 was about 200 Hz and decreased to 12 Hz at high ionic strength (1 M). At low frequencies (f≪f 0) the capacitance increment became frequency independent. It was, however, dependent on Na+ concentration and on the membrane potential which was generated by the charge transferred. A simple model is presented to analyze the experimental data quantitatively as a function of two parameters, the capacitance of the adsorbed membrane fragments, C P, and the potential of maximum capacitance increment, ψ 0. Below 5 mm Na+ a negative capacitance change was detected which may be assigned to electrogenic Na+ binding to cytoplasmic sites. It could be shown that the results obtained by experiments with the presented alternating current method contain the information which is determined by current-relaxation experiments with cell membranes.
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Received: 3 November 1997 / Revised version: 19 February 1998 / Accepted: 21 February 1998
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Sokolov, V., Stukolov, S., Darmostuk, A. et al. Influence of sodium concentration on changes of membrane capacitance associated with the electrogenic ion transport by the Na,K-ATPase. Eur Biophys J 27, 605–617 (1998). https://doi.org/10.1007/s002490050172
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DOI: https://doi.org/10.1007/s002490050172