Figure 2. The effect of sodium pump inhibition.

The model was initiated with variables derived from the final results shown in Fig. 1, and therefore all variables were initially stable. For clarity, [X⁻]_i is not shown, as it is membrane impermeant, and thus its concentration is straightforwardly related to V_c. At the point marked *, sodium pump density was reduced to zero, to simulate total sodium pump inhibition. Note the rapid small upward step in E_m that resulted from the loss of the electrogenic pump activity. Following this there was a gradual slower depolarization as [K⁺]_i and [Na⁺]_i began to equilibrate with the extracellular fluid. This depolarization allowed [Cl⁻] influx and thus volume increase. At the point marked †, sodium pump density was returned to its original value. Note that V_c, E_m and all intracellular ion concentrations returned to their starting values.