The role of intracellular buffers in acid-base disturbances: mathematical modelling.

Shifts of Na+, K+, Cl- and HCO3- between the cells and extracellular fluid of nephrectomized mammals in acute response to hypercapnia and to HCl or KCl infusion are simulated in steady state models involving just intracellular buffering and a simply defined interdependence of ionic gradients. Such models integrate diverse kinds of data and suggest new interpretations. In respiratory acidosis K+, HCO3- and water leave some cells and move both to where chemical buffering is least (ECF and other cells) and to cells that regulate pH particularly well by active transport. Buffering by erythrocytes is important, but the effects of distinguishing erythrocytes from other cells in a model is mainly just to emphasize Cl- movements. Effects of departures from the mammalian norm of body composition are explored.