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

The transepithelial transport of inorganic carbon to endolymph and its subs equent deposition on otoliths were pharmacologically examined by incubating the sacculus containing an otolith with (NaHCO3)-C-14. Calcium incorporati on was also studied. Carbon incorporation into endolymph and otoliths was s aturated with increased concentrations of bicarbonate ions in the incubatio n 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 incr ease in chloride concentrations in the medium. Calcium incorporation was no t affected by chloride and bicarbonate ions up to 10 mM. Higher concentrati ons of bicarbonate ions reduced calcium incorporation into both fractions. Carbon incorporation into endolymph and otoliths was inhibited by acetazola mide, disulfonate stilbenes (DIDS and SITS), thiocyanate, and ouabain. Calc ium incorpora tion was not affected by these inhibitors. Amiloride inhibite d carbon incorporation into otoliths alone. These results suggest that HCO3 --ATPase and Cl-/HCO3--exchangers are involved in the transepithelial trans port of bicarbonate ions to the endolymph. Carbonic anhydrase was also sugg ested to play a role in carbonate production for otolith calcification. (C) 2001 Elsevier Science Inc. All rights reserved.