Early effects of acetazolamide on anionic activities of the guinea pig endolymph: evidence for active function of carbonic anhydrase in the cochlea.
The effect of acetazolamide (ACZ) on HCO3- and Cl- activities in inner ear fluid was investigated by ion-selective microelectrode methods. The endocochlear potential, at 81.6 +/- 1.5 mV under normal conditions, was reduced by 4.9 +/- 0.9 mV in 30 min following the ACZ injection. The HCO3- concentrations by 11.5 +/- 1.7 mM in 30 min, while the change of Cl- level was not consistent but showed a tendency toward slight increase in average. The calculated PCO2 in endolymph was 39.6 mmHg. ACZ induced a constant elevation of the endolymph PCO2, with an increase in the venous PCO2 during the initial 20 min and thereafter the endolymph PCO2 attained a plateau despite the continuous increase of the venous PCO2. We postulate that the HCO3- secretion into the endolymph is mediated by carbonic anhydrase (CAH) and is decreased by ACZ due to the inhibition of CAH.
Ikeda
K
K
Department of Otolaryngology, Tohoku University School of Medicine, Sendai, Japan.
Kusakari
J
J
Takasaka
T
T
Saito
Y
Y
D000086:Acetazolamide / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004710:Endolymph / Q000201:enzymology*; D006168:Guinea Pigs; D007761:Labyrinthine Fluids / Q000201:enzymology*; D010498:Perilymph / Q000201:enzymology; D013997:Time Factors
D001639:Bicarbonates; D002712:Chlorides; D002256:Carbonic Anhydrases; D000086:Acetazolamide