[Rapid pH changes associated with synaptic transmission in isolated slices of the mammalian hippocampus]

To perform rapid optical detection of possible pH changes accompanying electrical activity hippocampal slices were stained with pH indicator--phenol red (0.2 mM). Electrical response of granular and pyramidal cells was evoked by stimulation of perforant path, Schaffer collateral and commissural afferents in the stratum radiatum. Biphasic pH changes occurred both in pyramidal and granular cells: rapid acid changes, with the maximum reached in several msec, were followed by alkaline changes lasting up to one sec. pH changes disappeared with the blocking of synaptic transmission by Mg2+ (10 mM) and were absent in antidromic stimulation of granular cells. pH changes are believed to be related to the processes accompanying synaptic transmission.