Ammonium prepulse: effects on intracellular pH and bioelectric activity of CA3-neurones in guinea pig hippocampal slices.
The ammonium prepulse technique was used to study influences of intracellular pH (pH(i)) on bioelectric activity of CA3-neurones in hippocampal slices. 60, 180 or 600 s lasting NH(4)Cl (10 mM) pulses led to a transient intracellular alkalosis (DeltapH(i): up to 0.2 pH-units) in about one-half of the neurones loaded with 2', 7-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-acetoxymethylester (BCECF-AM). No alkalosis was seen in the remainder cells. The amount of alkalosis depended on the actual pH(i) of each neurone and increased when the pH(i) decreased. Washout of NH(4)Cl induced a fall in pH(i) (DeltapH(i): 0.12-0.54 pH-units) which recovered within <20 min. Frequency of spontaneous action potentials remained unchanged during washin of ammonium (60 or 180 s). However, pre-treatment with low concentrations of bicuculline-methiodide (0. 01 microM) or caffeine (0.1 mM), both of which did not change bioelectric activity per se, permitted a burst-activity to occur during ammonium-washin in about one-half of the neurones. In all neurones, washout of ammonium inhibited spontaneous and epileptiform activity (elicited by 1 mM caffeine, 20-50 microM bicuculline-methiodide, or 50-75 microM 4-aminopyridine) for </=20 min. This inhibition was accompanied by an increased membrane conductance (up to 20%) and a hyperpolarisation of up to 10 mV. We conclude that intracellular alkalosis augments, whereas intracellular acidosis depresses bioelectric activity of CA3-neurones.
Bonnet
U
U
Rheinische Kliniken, Universitätsklinik für Psychiatrie und Psychotherapie, POB 10 30 43, D-45030, Essen, Germany.
Wiemann
M
M
D000471:Alkalosis / Q000139:chemically induced / Q000503:physiopathology; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D004594:Electrophysiology; D004827:Epilepsy / Q000503:physiopathology; D006168:Guinea Pigs; D006624:Hippocampus / Q000473:pathology / Q000503:physiopathology*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D009474:Neurons / Q000502:physiology*
D000643:Ammonium Chloride; D006859:Hydrogen