Cells regulate the activity of carbonic anhydrase (CA) in response to inhibition of the enzymes. Acute and chronic treatment with acetazolamide (a specific CA enzyme inhibitor) results in increased enzyme activity and increased amounts of CA in cells. The hypothesis of the present study is that the purpose of regulating carbonic anhydrase is to preserve the activity of the enyzme in subcellular fractions where it is essential for the normal functions performed by the cells. Inhibition or 99%+ of the enzyme activity in whole organs to produce anticonvulsant and other physiological effects obscures the significance of inhibition of the enzyme in subcellular locations where a significantly smaller percent inhibition would produce significant physiological effects. The purpose of the excess enzyme in organs, then, is to protect essential activity by 1) buffering inhibitors by binding them and 2) providing uninhibited enzyme to replace inhibited enzyme. Finally, in the absence of inhibitors excess enzyme is needed to ensure optimal activities in subcellular locations where physiological effects are exerted. This hypothesis will be tested by measuring the relation between anticonvulsant effects, as measured by electroshock seizure threshold (EST), maximal electroshock seizure (MES) and audiogenic seizure (AGS) pattern, and threshold to chemical convulsants, and 1) enzyme activity and 2) the amount of enzyme present in subcellular fractions following acute and chronic inhibition with acetazolamide. This study will be performed in the context of the development of tolerance to the antiepileptic effects of acetazolamide in apparently normal mice (C57BL/J6) and in mice with an inborn error of CA regulation (DBA/2J audiogenic seizure strain). Measurable physiological endpoints (protection from MES, AGE; effects on EST and on chemically- induced) seizures and relevance to a human clinical problem are available with this approach.
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