16 – Intracellular pH Regulation

Publisher Summary This chapter discusses that virtually all the H ions within a cell are buffered by reversible binding to weak acids and bases, resulting in a low free H ion concentration. Therefore, the concentration of free H ions within the cytoplasm is expressed as cytoplasmic pH (pHi), which is a more convenient scale for molecules at low concentrations. Cytoplasmic pH is an important aspect of the intracellular milieu and can affect nearly all aspects of cell function. In most cells, pHi is maintained at a value of about 7.0, well alkaline to the equilibrium pHi, calculated on the assumption that H ions are at equilibrium across the membrane. The fact that pHi is alkaline to its equilibrium value creates a passive acidifying influx of H ions. Most cells face a continuous acid load not only because of this acidifying influx but also because of metabolic acid production and leakage from internal acidic compartments. The chapter also explains that changes in pHi affects many cellular functions. Cell metabolism is affected by changes in pH, predominantly because of pH-sensitive metabolic enzymes, like phosphofructokinase. Changes of pHi also affect the cross linking and polymerization of cytoskeletal elements, such as actin and tubulin. The chapter discusses that the pH of certain organellar compartments differ from the value of pHi and these differences in pH are important for organellar function.