Alteration of intracellular pH and activity of CA3-pyramidal cells in guinea pig hippocampal slices by inhibition of transmembrane acid extrusion

Transmembrane acid extruders, such as electroneutral operating Na+/H+-excha ngers (NHE) and Na+-dependent Cl-/HCO3- exchangers (NCHE) are essential for the maintenance and regulation of cell volume and intracellular pH (pH(i)) . Both of them are hypothesised to be closely linked to the control of exci tability. To get further information about the relation of neuronal pH(i) a nd activity of cortical neurones we investigated the effect of NHE- and/or NCHE-inhibition on (i) spontaneous action potentials and epileptiform burst -activity (induced by bicuculline-methiodide, caffeine or 4-aminopyridine) and (ii) on pH(i) of CA3-neurones. NHE-inhibition by amiloride (0.25-0.5 mM ) or its mon potent derivative dimethylamiloride (50 mu M) and NCHE-inhibit ion by 4,4'-diisothiocyanostilbene-,2,2'-disulfonic acid (DIDS, 0.25-0.5 mM ) induced a biphasic alteration of neuronal activity: an initial, up to 30 min lasting, increase in frequency of action potentials and bursts preceded a growing and partially reversible suppression of neuronal activity. In BC ECF-loaded neurones the pH(i), however, continuously decreased during eithe r amiloride- or DIDS-treatment and reached its steady-state (Delta pH(i) up to 0.3 pH-units) when the neuronal activity was markedly suppressed. Combi ned treatment with amiloride (0.5 mM) and DIDS (0.5 mM) or treatment with h armaline alone (0.25-0.5 mM), which also continuously acidified neurones vi a inhibition of an amiloride-insensitive NHE-subtype, induced a monophasic and partially reversible suppression of neuronal activity. As an initial ex citatory period failed to occur during combined NHE/NCHE-inhibition we spec ulate that its occurrence during amiloride- or DIDS-treatment resulted rath er from disturbances in volume- than in pH(i)-regulation. The powerful inhi bitory and anticonvulsive properties of NHE- and NCHE-inhibitors, however, very likely based upon intracellular acidification - as derived from our pr evious findings that a moderate increase in intracellular free protons is s ufficient to reduce membrane excitability of CA3-neurones. (C) 2000 Elsevie r Science B.V. All rights reserved.