EFFECTS OF CALCIUM-ANTAGONISTS AND OTHER METABOLIC MODULATORS ON IN-VITRO CALCIUM DEPOSITION ON OTOLITHS IN THE RAINBOW-TROUT ONCORHYNCHUS-MYKISS

Translocation of blood calcium to otoliths across the saccular epithel ium was examined pharmacologically using an isolated preparation of th e otolith-containing sacculus from rainbow trout. Mannitol added to th e incubation medium virtually did not permeate into endolymph, indicat ing that intercellular junctions are tight for calcium to diffuse thro ugh 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 me dium did not change the rate of calcium deposition on otoliths, ouabai n reduced the rate in a concentration-dependent way. Chlorpromazine wa s also effective for the reduction. These results suggest that recepto r-operated calcium channels facilitate calcium influx into saccular ce lls across the basolateral membrane and that cytosolic calcium is extr uded to the otolith across the distal membrane by the Na+-Ca2+ exchang er and ATP-dependent calcium pump.