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Abstract. Excretion of total CO2 and uptake of sodium and chloride ions across the branchial epithelium of the posterior gills of the shore crab Carcinus maenas, collected from Kiel Bay (Baltic Sea) in 1989, were measured using isolated perfused gill preparations. Total CO 2 effluxes depended on the HCO~-concentration of the internal perfusate in a saturable mode and were inhibited by internally and externally applied acetazolamide at 10-4 M. Potential differences between hemolymph space and medium did not change significantly during experimental treatments. Neither a bicarbonate gradient (6 mM) directed from the internal perfusate to external bath solution nor symmetrically applied 10-4 M acetazolamide significantly influenced the influxes of Na + and C1-. Results confirmed the role of carbonic anhydrase in CO 2 excretion but called into question the assumed functioning of the enzyme in branchial ion transport processes.

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