Measurement of pH and ionic composition of pericellular sites.

The development of ion selective microelectrodes has made it possible to measure the normal steady state in the pericellular environment together with ion fluxes in response to physiological or pathological disturbances. Combined intracellular and extracellular measurements indicate that there is a considerable range of ability between various types of cells in the efficiency with which they can tolerate changes in pericellular conditions. Macrophages are extremely tolerant while cells of the cerebral cortex require a very finely controlled local environment. Combination of ion selective probes with microelectrodes which measure substrate and oxygen availability extend the information which can be obtained about ionic composition of cellular environment and the factors which are important in its homostasis.