Carbonic anhydrase inhibitor sulthiame reduces intracellular pH and epileptiform activity of hippocampal CA3 neurons.
OBJECTIVE
Sulthiame is a carbonic anhydrase (CA) inhibitor with an anticonvulsant effect in the treatment of benign and symptomatic focal epilepsy in children. The aim of the study was to elucidate the mode of action of sulthiame with respect to possible changes of intracellular pH (pHi) that might develop along with sulthiame's anticonvulsant properties.


METHODS
The effects of sulthiame (a) on pHi of 2',7-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-acetoxymetyl ester (BCECF-AM) loaded CA3 neurones as well as (b) on epileptiform activity (induced by 50 microM 4-aminopyridine) were compared with those of the CA inhibitors acetazolamide and benzolamide.


RESULTS
In the majority of neurons, sulthiame (1.0-1.5 mM; n = 8) as well as the membrane permeant acetazolamide (0.5-1.0 mM; n = 6) reversibly decreased pHi by 0.18 +/- 0.05 (SD) and 0.17 +/- 0.10 (SD) pH units, respectively, within 10 min. The poor membrane permeant benzolamide (1.0-2.0 mM) had no influence on pHi (n = 8). Sulthiame (1.0-2.5 mM) and acetazolamide (1.0-2.0 mM) reversibly reduced the frequency of action potentials and epileptiform bursts after 10-15 min (n = 9, n = 7), whereas benzolamide (1.0-2.0 mM) had no effect (n = 6).


CONCLUSIONS
The results suggest that sulthiame acts as a membrane-permeant CA inhibitor whose beneficial effect on epileptiform activity results at least in part from a modest intracellular acidosis of central neurons.
Leniger
Tobias
T
Department of Neurology, University of Essen, Essen, Germany. tobias.lenger@uni-essen.de
Wiemann
Martin
M
Bingmann
Dieter
D
Widman
Guido
G
Hufnagel
Andreas
A
Bonnet
Udo
U
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology; D001574:Benzolamide / Q000494:pharmacology; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology*; D004827:Epilepsy / Q000378:metabolism / Q000517:prevention & control*; D006168:Guinea Pigs; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D013843:Thiazines / Q000494:pharmacology*; D000096926:Benzenesulfonamides
D000086:Acetazolamide; D000927:Anticonvulsants; D001574:Benzolamide; D002257:Carbonic Anhydrase Inhibitors; D013843:Thiazines; C084593:sulthiame; D000096926:Benzenesulfonamides