. 2015 Jun 24;309(5):F434–F446. doi: 10.1152/ajprenal.00539.2014

Table 1.

Experimental settings used to solve the optimization problem in Eqs. 7–9 and to carry out the ion net flux simulations in Figs. 3–5

	Experiment 1 (bath K⁺ concentration varies)		Experiment 2 (bath NH₄⁺ concentration varies)		Experiment 3 (bath Na⁺ concentration varies; bath NH₄⁺ concentration = 0)
Solute	Lumen	Cytosol	Lumen	Cytosol	Lumen	Cytosol
Na⁺	20	20	20	20	(0, 5, 20, 50)
K⁺	(0, 0.15, 0.3, 0.6, 1.2, 2.5, 5, 10, 20)		0	0	5	5
pH	7.2	7.2	7.2	7.2	7.2	7.2
NH₄⁺	0	0	(0, 0.15, 0.3, 0.6, 1.2, 2.5, 5, 10, 20)		0	0
ATP		3		3		3
ADP		0.04^*		0.04^*		0.04^*
P_i		5^*		5^*		5^*

	Experiment 4 (bath Na⁺ concentration varies; bath K⁺ concentration = 0)		H⁺-to-K⁺ Net Flux Ratio		Net Flux Simulations		Fig. 2 in Weinstein's IMCD Model (43)
Solute	Lumen	Cytosol	Lumen	Cytosol	Lumen	Cytosol	Lumen	Cytosol
Na⁺	(0, 5, 20, 50)		147	15†	25	15†	0	0
K⁺	0	0	5	120†	5	120†	20	150
pH	7.2	7.2	7.4	7.2†	7.0	7.2†	(0.3–8)	7.4
NH₄⁺	5	5	0	0‡	2	2	0	0
ATP		3		2^*		2^*		2^*
ADP		0.04^*		0.04^*		0.04^*		0.04^*
P_i		5^*		5^*		5^*		5^*

Ion concentrations are shown in mM, pH is dimensionless. If not otherwise specified, ion concentrations in experiments 1–4 are in accordance with the experimental setting in Ref. 9, where apical membranes extracted from the rat distal colon were bathed in different solutions, independently, to perform the ATPase activity assays. For H⁺-to-K⁺ net flux ratio and Figure 2 in Weinstein's IMCD model (43) (where IMCD is inner medullary collecting duct), ion concentrations are in accordance with the experimental settings in Refs. 16 and 43, respectively.

Assumed as in Ref. 43; †assumed as in Ref. 5 for a typical cell; ‡assumed to be negligible under an in vitro setting.