Intracellular pH transients induced by Co2 or NH3

Experiments are reviewed in which intracellular pH (pHi), during exposure of a cell to CO2- or NH3-containing solutions, not only undergoes an acidification of alkalinization, respectively, but tends to return toward its original value and, upon removal of the test solution, rebounds to a value more alkaline or acid, respectively, than the initial one. A simple physiochemical model is discussed which interprets these observations both qualitatively and quantitatively. In the case of NH3-induced transients, only passive movements seem to take place; in the CO2-induced transients one must postulate an active 'proton pump'. Experimentally verifiable predictions can be made from these models. It is suggested that many physiological effects follow exposure to CO2 or NH3 may be subject to similar transients and rebounds.