ABSTRACT
The measurement of intracellular pH is based on monitoring the equilibrium distribution of a membrane-permeant weak electrolyte between the intracellular and extracellular spaces. The calculation of intracellular pH by distribution techniques is based on the estimate of the intracellular or intraorganellar concentration of the pH-indicating substance, but the usual techniques yield a value of the total amount of the indicator present, e.g., in the supernatant, pellet, filtrate, or filter. The temporal resolution of distribution techniques is principally limited by the time needed for the equilibration of the distributive indicator between the intracellular and extracellular space. If a slowly responding technique for monitoring the indicator concentration is used, the overall time resolution is further decreased. To obtain the intracellular concentration the total intracellular indicator value and the intracellular water volume must be calculated. The distribution method, therefore, involves the determination of intra- and extracellular water.
