Effects of enzyme and anion transport inhibitors on in vitro incorporation of inorganic carbon and calcium into endolymph and otoliths in salmon Oncorhynchus masou

Abstract

The transepithelial transport of inorganic carbon to endolymph and its subsequent deposition on otoliths were pharmacologically examined by incubating the sacculus containing an otolith with NaH 14CO 3. Calcium incorporation was also studied. Carbon incorporation into endolymph and otoliths was saturated with increased concentrations of bicarbonate ions in the incubation medium and was followed by the Michaelis–Menten equation with a K m of 26.3 mM and 0.4 mM, respectively. Carbon incorporation decreased with an increase in chloride concentrations in the medium. Calcium incorporation was not affected by chloride and bicarbonate ions up to 10 mM. Higher concentrations of bicarbonate ions reduced calcium incorporation into both fractions. Carbon incorporation into endolymph and otoliths was inhibited by acetazolamide, disulfonate stilbenes (DIDS and SITS), thiocyanate, and ouabain. Calcium incorporation was not affected by these inhibitors. Amiloride inhibited carbon incorporation into otoliths alone. These results suggest that HCO 3 −-ATPase and Cl −/HCO 3 −-exchangers are involved in the transepithelial transport of bicarbonate ions to the endolymph. Carbonic anhydrase was also suggested to play a role in carbonate production for otolith calcification.