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Depolarization increases the apparent affinity of the Na + ‐K + pump to cytoplasmic Na + in isolated guinea‐pig ventricular myocytes
Author(s) -
Barmashenko Gleb,
Kockskämper Jens,
Glitsch Helfried G.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0691s.x
Subject(s) - depolarization , tetraethylammonium , chemistry , membrane potential , diaphragm pump , biophysics , intracellular , analytical chemistry (journal) , potassium , biochemistry , materials science , chromatography , nanotechnology , biology , organic chemistry , micropump
1 In order to investigate the possible effect of membrane potential on cytoplasmic Na + binding to the Na + ‐K + pump, we studied Na + ‐K + pump current‐voltage relationships in single guinea‐pig ventricular myocytes whole‐cell voltage clamped with pipette solutions containing various concentrations of Na + ([Na + ] pip ) and either tetraethylammonium (TEA + ) or N ‐methyl‐D‐glucamine (NMDG + ) as the main cation. The experiments were conducted at 30 °C under conditions designed to abolish the known voltage dependence of other steps in the pump cycle, i.e. in Na + ‐free external media containing 20 mM Cs + . 2 Na + ‐K + pump current ( I p ) was absent in cells dialysed with Na + ‐free pipette solutions and was almost voltage independent at 50 mM Na + pip (potential range: −100 to +40 mV). By contrast, the activation of I p by 0.5–5 mM Na + pip was clearly voltage sensitive and increased with depolarization, independently of the main intracellular cation species. 3 The apparent affinity of the Na + ‐K + pump for cytoplasmic Na + increased monotonically with depolarization. The [Na + ] pip required for half‐maximal I p activation ( K 0.5 value) amounted to 5.6 mM at −100 mV and to 2.2 mM at +40 mV. 4 The results suggest that cytoplasmic Na + binding and/or a subsequent partial reaction in the pump cycle prior to Na + release is voltage dependent. From the voltage dependence of the K 0.5 values the dielectric coefficient for intracellular Na + binding/translocation was calculated to be ≈0.08. The voltage‐dependent mechanism might add to the activation of the cardiac Na + ‐K + pump during cardiac excitation.