Objective To investigate the localization of Ca 2+ -ATPase (Ca 2+ pump) in the cochlear and its change after endolymphatic hydrops, and to study the relationship between compound action potential (CAP) threshold and the Ca 2+ -ATPase activety.Methods The left endolymphatic sac was ablated to induce endolymphatic hydrops in fourteen healthy guinea pigs with normal action potential thresholds measured after a sliver ball electrode placed on the round window. Ca 2+ -ATPase activity was studied cytochemically using a lead citrate reaction in control and hydropic ears. The reaction product was lead phosphate particles as an expression of Ca 2+ -ATPase activity, observed with an eletron microscope. Results Ca 2+ -ATPase activity is mainly found on the endolymphatic surface of Reissner’s membrane, the stereocilia and cuticular plate of inner and outer hair cells, and along the infolded plasma membrane of strial marginal cells. CAP thresholds of filtered click are increased and Ca 2+ -ATPase activity significantly decreased after endolymphatic hydrops in the mentioned locations. Conclusions CAP thresholds are increased and Ca 2+ -ATPase activity are significantly decreased in the cochlea after endolymphatic hydrops. These results suggest that there is a negative correlation between them.
