Effects of “simplified” and “realistic” conditions and other parameters on the relation between Na⁺/K⁺-pump activity, <i>E</i>_<i>m</i> and the cell volume.

A: Dependence of [Na+]i, [K+]i, (scale on the left), and Em (scale on the right) on activity of the electrogenic Na+/K+-pump with gK:gNa = 9:1 in “simplified” (see Methods for explanations) conditions. B: The same as in part A, but in “realistic” (see text and Methods for explanations) conditions. C: Dependence of [Na+]i, [K+]i, (scale on the left), and Em (scale on the right) on activity of the only Na+ pump (3 Na+ per ATP) in “simplified” conditions. gK = gNa. D: The same as in part C, but in “realistic”. E: Dependence of Em on activity of the Na+/K+-pump activity in both “simplified” (open squares) and “realistic” (closed circles) conditions and under four different settings; the parameters of the settings are described in the text. F: Dependence of the cell volume (in % of original volume, i.e. in passive situation with no pumping) on activity of the Na+/K+-pump in the same conditions and settings as in part E. Initial conditions (A–D): [Na+]o = 145 mM; [K+]o = 5 mM; [Cl-]o = 150 mM; (A, B): gNa = 2*109 ions/(sec*V); gK = 1.8*1010 ions/s*V; 3Na+/2K+ pump; (C, D): gNa = gK = 1010 ions/s*V; 3Na+/0K+ pump; (A, C): [Na+]i = 145 mM; [K+]i, = 5 mM; [Cl-]i = 15 mM; [An-]i = 135 mM; z = -1; (B, D): [neutral osmolyte]o = 6 mM; [Na+]i = 174.0 mM; [K+]i = 6.0 mM; [Cl-]i = 18.0 mM; [An-]i = 108.0 mM; z = -1.5. (A-F) The pump activity is presented as ATP molecules spent per second and displayed in engineering notation with M for millions.