Ž . Brain Research 796 1998 161–170 Research report CO rHCO y -withdrawal from the bath medium of hippocampal slices: 2 3 biphasic effect on intracellular pH and bioelectric activity of CA3-neurons Udo Bonnet a, ) , Martin Wiemann b , Dieter Bingmann c a Rheinische Kliniken, UniÕersitatsklinik fur Psychiatrie und Psychotherapie, POB 103043, D-45030 Essen, Germany ¨ ¨ b Institut fur Physiologie, UniÕersitat-GH Essen, Hufelandstr. 55, D-45122 Essen, Germany ¨ ¨ c Institut fur Physiologie, UniÕersitat-GH Essen, Hufelandstr. 55, D-45122 Essen, Germany ¨ ¨ Accepted 24 March 1998 Abstract Many studies analyzing interactions of pH and bioelectric activity focus on changes of the extracellular pH, whereas data concerning Ž . central neuronal excitability and intracellular pH pH are rare. Here, we report on the spontaneous bioelectric activity and epileptiform i activity of CA3-neurons during a procedure which changed pH . As monitored in BCECF-AM loaded cells, the change from a i y Ž y . CO rHCO -buffered to a HEPES-buffered medium CO rHCO -withdrawal, hereafter termed W was associated with a transient 2 3 2 3 Ž . Ž . intracellular alkalosis D pH s0.2 "0.04 which preceded a sustained intracellular acidosis D pH s0.4 "0.04 . Coinciding with this W-induced biphasic shift of pH a biphasic alteration of spontaneous bioelectric activity was recorded: as a rule, an up to 30 min lasting i Ž . Ž . increase excitatory phase preceded a typical sustained suppression inhibitory phase . This biphasic action was also observed using Ž . various in vitro-epilepsy-models bicuculline, penicillin, caffeine : epileptiform discharges were completely suppressed after an initial increase in frequency. This modulation of bioelectric activity was unlikely due to alterations of the postsynaptic GABA-system as hyperpolarizing GABA - and GABA -responses of CA3-neurons were hardly affected. In the majority of the neurons, the initial increase A B Ž . of spontaneous bioelectric activity excitatory phase culminated in transient burst periods lasting 5–30 min. These transient burst periods Ž . were blocked by NMDA- or AMPA-antagonists: DL-2-amino-5-phosphonovalerate APV, 50 mM or 6-cyano-7-nitroquinoxaline-2,3-di- Ž . Ž . one CNQX, 50 mM . The calcium-antagonist verapamil 50 mM reduced amplitudes of depolarizations and duration of the transient burst periods. The results suggest that the biphasic alteration of pH modulates the susceptibility of glutamate receptors and voltage-gated i calcium-channels, which leads to respective changes of bioelectric activity. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Neuronal excitability; Epilepsy; Intracellular pH; Glutamate; GABA; HEPES; Hippocampal slice 1. Introduction Many central diseases such as stroke, epilepsy and also panic attacks are associated with alterations of the extracel- Ž . w x lular pH pH of brain tissue 17,40,51,55,56 . It appears e that elevation and fall of pH induce an increase and e decrease of excitability of central neurons, respectively w x 3,4,6,15,17,18,20,57 . This effect is possibly due to pH dependent modulations of transmembrane channels andror w x receptors 18,62,63,65,67 . In a couple of in vitro-studies, alterations of the pH-milieu were achieved by varying y w x CO rHCO -buffers in the media 3,6,20,38,57 . Hyper- 2 3 capnia or reduction of HCO y in artificial cerebrospinal 3 fluid were followed by a decrease of excitability and spontaneous bioelectric activity of central neurons ) Corresponding author. Fax: q49-201-7227-444. w x y 6,38,57 . In contrast, raised extracellular HCO generated 3 epileptiform activity in hippocampal and neocortical pyra- w x midal neurons 3,21,20 . These changes in bioelectric ac- tivity could also be due to alterations of the intracellular Ž . w x pH pH 9,35,36,38,61 resulting from, e.g., transmem- i brane diffusion of CO , permeation of protons and HCO y 2 3 through membrane channels andror altered acid-extrusion w x 11,16–18,32,49,52,54 . Moreover, ethacrynic acid, a loop diuretic supposed to decrease pH , led to a sustained i w x suppression of neuronal excitability 12 . To get more information about the interactions of cen- tral excitability and pH , we studied the spontaneous bio- i electric activity and epileptiform activity of CA3-neurons y Ž during the withdrawal of CO rHCO hereafter termed 2 3 . W from the bath medium of hippocampal slices. This technique was used because it should primarily change pH i w x 22 . Thus, W was demonstrated to induce a biphasic shift 0006-8993r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.