Figure 3

Simulation results of ion concentrations, membrane potential and cell volume for healthy and pump inhibited CHO cells in 1.7 S/m medium. The model is initiated with intracellular ion concentrations close to equilibrium with extracellular fluid except the chloride concentration which is lower due to the intracellular organic anions ([Na⁺]_i = 145 mM, [K⁺]_i = 12 mM, [Cl⁻]_i = 60 mM, [X⁻]_i = 83 mM). V_c is initially defined as 9 × 10⁻¹⁰ cm³. The parameters such as ion permeabilities and Na⁺/K⁺ ATPase pump density are as specified in Table 2. Ion concentrations at steady state are [Na⁺]_i = 11 mM, [K⁺]_i = 145 mM, [Cl⁻]_i = 70 mM and [X⁻]_i = 74 mM. At the point marked with dash line, after 150 minutes, the Na⁺/K⁺ ATPase pump density is reduced to zero, to simulate total Na⁺/K⁺ ATPase pump inhibition. At this time, the model is initiated with variables derived from the results of the first 150 minutes, marked with dash line, and therefore all variables are initially stable. After pump inhibition, there is a gradual depolarization as [K⁺]_i and [Na⁺]_i begin to equilibrate with the extracellular fluid. This depolarization allows [Cl⁻]_i influx and thus volume increases.