ABSTRACT
Attempts to define intracellular regions of different pH have been many, and it has, indeed, been possible to assign a distinct pH to plant or yeast vacuoles and even to mitochondria. The observation that digestive intracellular organelles may be more acid than the cytosol is now considered an established fact, and hydrogen ion pumps are known to operate in their membranes, with the obvious purpose of keeping the intraorganellar pH low, which is helpful to their hydrolytic function. The living cell exhibits heterogeneity in intracellular pH due both to internal compartmentation and to pH differences within the compartments. Recent measurements of extracellular pH values with single- and double-barreled glass microelectrodes showed significant differences between the bulk extracellular value, the value close to the external surface, and the intracellular value of various muscle cells.
