Modulation of extracellular pH by glutamate and GABA in rat hippocampal slices.
1. Alkaline extracellular pH transients evoked by afferent stimulation, and local pressure ejection of glutamate and gamma-aminobutyric acid (GABA), were studied in the CA1 region of rat hippocampal slices. Amino acid-evoked responses were obtained by use of a dual micromanipulator, with the tip of a double-barreled pH-sensitive microelectrode positioned 50 microns from a pressure ejection pipette. 2. At 31 degrees C, in Ringer solutions buffered with 26 mM HCO3- and 5% CO2, mean extracellular pH in submerged 300-microns slices was 7.15 +/- 0.12 (n = 27 slices), at a tissue depth of approximately 150 microns. In Ringer buffered with 35 mM HCO3- and 5% CO2, extracellular pH was 7.29 +/- 0.10 (n = 19 slices). 3. Repetitive stimulation of the Schaffer collaterals caused an extracellular alkaline shift in stratum oriens, pyramidale, and radiatum, averaging 0.05 +/- 0.03 pH units among all regions (n = 138), with a maximum response of 0.16 pH units. Alkaline transients of similar appearance were obtained by local ejection of glutamate (0.01-0.12 pH units, n = 110) and GABA (0.01-0.18 pH units, n = 137). Control ejection of these amino acids into dilute agar caused only small acid shifts. 4. Superfusion of 100 microM picrotoxin abolished the GABA-evoked alkaline shift but failed to inhibit the Schaffer collateral- and glutamate-evoked alkalinizations. 5. Superfusion of 10(-5)-10(-3) M acetazolamide acidified the baseline by 0.05-0.10 pH units and amplified the Schaffer collateral- and glutamate-evoked alkaline shifts.(ABSTRACT TRUNCATED AT 250 WORDS)
Chen
J C
JC
Department of Physiology and Biophysics, New York University Medical Center, New York 10016.
Chesler
M
M
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001574:Benzolamide / Q000494:pharmacology; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists; D005110:Extracellular Space / Q000378:metabolism* / Q000502:physiology; D005260:Female; D018756:GABA Antagonists; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D000086:Acetazolamide; D001574:Benzolamide; D002257:Carbonic Anhydrase Inhibitors; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D005971:Glutamates; D018698:Glutamic Acid; D010852:Picrotoxin; D005680:gamma-Aminobutyric Acid