Fig. 3.

A: 1H⁺(1Na⁺)-1K⁺(1NH₄⁺)-ATPase ion net flux as a function of luminal ion concentration, assuming that the total density of protein E_T is 1 pmol/mm tubule. When not varied, lumen and cytosol [Na⁺], [K⁺], [NH₄⁺], and pH were set as in Table 1 (Net flux simulation). Positive fluxes are into the cell, and negative fluxes are out of the cell. H⁺ flux reverses at a luminal pH (pH_l) of ∼5.6 (solid circle). B: 1H⁺(1Na⁺)-1K⁺(1NH₄⁺)-ATPase ion net flux as a function of cytosolic ion concentration, assuming that the total density of protein E_T is 1 pmol/mm tubule. When not varied, lumen and cytosol [Na⁺], [K⁺], [NH₄⁺], and pH were set as in Table 1 (Net flux simulation). Graphs in a and c were zoomed to appreciate small-scale ion net fluxes (left). Positive fluxes are into the cell, and negative fluxes are out of the cell. Na⁺ flux reverses at a cytosolic pH (pH_c) of ∼3.7 (solid circle).