Regulation of intracellular pH in eukaryotic cells.

The fact that cytoplasmic pH is strictly regulated has only been appreciated during the last 10 years. Eukaryotic cells clamp cytoplasmic pH at 7.0-7.4 by ion transport mechanisms and a high buffering capacity of the cytosol. The values of internal pH observed (pH 7.0-7.4) are higher than expected if the protons had been passively distributed across the cell membrane according to electrochemical gradients. Thus, when the membrane potential is -59 mV, pHi should be 1 unit less than pHo. The equilibrium relation between membrane potential, Vm, and internal and external H+ concentrations is given by the Nernst expression: