Basic Principles of pH Regulation
The pH of a cell is an important attribute of its internal environment. 1 – 4 Intracellular pH, pHi (referring only to cytoplasmic pH), affects, among other things, membrane transport systems and conductances, enzyme activities, and communication between cells through gap junctions. Changes in pHi can serve a messenger function for external stimuli, including hormones such as insulin, a variety of growth-promoting factors, and sperm, upon activation of eggs. Internal pH can also interact with other cellular messengers such as Ca and cAMP. Finally, the maintenance of pH differences between cytoplasm and intracellular organelles such as lysosomes and mitochondria is integral to the function of these cellular components. Thus, it is not surprising that cells have developed mechanisms for the regulation of pHi and that the activity of these mechanisms is controlled by external as well as internal factors.