Effects of Calcium Antagonists and Other Metabolic Modulators on in Vitro Calcium Deposition on Otoliths in the Rainbow Trout Oncorhynchus mykiss

Abstract

Translocation of blood calcium to otoliths across the saccular epithelium was examined pharmacologically using an isolated preparation of the otolith-containing sacculus from rainbow trout. Mannitol added to the incubation medium virtually did not permeate into endolymph, indicating that intercellular junctions are tight for calcium to diffuse through a paracellular pathway. The addition of lanthanum or gadolinium to the incubation medium led to a marked decrease in the rate of calcium deposition on otoliths. Verapamil and diltiazem had no effect on the deposition, while Reactive blue reduced the rate to 60% of the control. Although the replacement of sodium with choline in the incubation medium did not change the rate of calcium deposition on otoliths, ouabain reduced the rate in a concentration-dependent way. Chlorpromazine was also effective for the reduction. These results suggest that receptor-operated calcium channels facilitate calcium influx into saccular cells across the basolateral membrane and that cytosolic calcium is extruded to the otolith across the distal membrane by the Na+-Ca2+ exchanger and ATP-dependent calcium pump. © 1995, The Japanese Society of Fisheries Science. All rights reserved.