The relationships between monovalent ion fluxes via major cell membrane pathways (Na/K pump, NaK2Cl symporter, electroconductive sodium, potassium and chloride channels) and steady state transmembrane ion distribution, membrane potential and cell water content were calculated for the high potassium animal cells with high and low membrane potential. It is found that variation in NaK2Cl symport or chloride electroconductive permeability causing changes in cell water content of high magnitude do not lead to significant changes in the intracellular Na/K ratio or membrane potential, in contrast to the effects caused by variation in the Na/K pump fluxes or permeability of the Na and K channels. It is shown that water content in cells with a high membrane potential, e.g. of about 70 mV, cannot be increased due to an increase in NaK2Cl symport by more than 1.6 times. In cells with a low membrane potential an increase in symport leads to a decrease in water content, which is also limited. In cells with membrane potential of about 10 mV the water content cannot be decreased more than by 1.8 times. When NaK2Cl symporter is operating, the effect of chloride channel permeability on the ion and water balance is quite opposite to the symport and is limited by the same boundaries. It is shown that effects caused by changes in symport and in chloride permeability can be differentiated only by the analysis of kinetic (fluxes, transport rate constants etc.) but not "static" characteristics of ion distribution. It is shown that under some circumstances the influence of NaK2Cl symport and chloride channel permeability on ion and water balance can be strong even at a very small symport share in the overall flux.
Animals Biological Transport, Active