Na+,K+-ATPase and Ca2+-ATPase activities in the cochlear lateral wall following surgical induction of hydrops

Na+,K+-ATPase and Ca2+-ATPase activities have not been studied quantitative ly in the cochlea affected by endolymphatic hydrops. The present study was designed to measure quantitatively the Na+,K+-ATPase and Ca2+-ATPase activi ties in the cochlear lateral wall and the threshold of auditory brainstem r esponse (ABR) for guinea pigs in the early stages (=2 months) of experiment ally induced endolymphatic hydrops. A significant negative association was demonstrated between Ca2+-ATPase activity and the change in ABR threshold f or hydropic cochleae (P=0.014), but not for control cochleae (P=0.123), alt hough no such significant association was revealed between Na+,K+-ATPase ac tivity and any change in ABR threshold for both hydropic cochleae (P=0.751) and control cochleae (P=0.352). A significant increase in Ca2+-ATPase acti vity in the cochlear lateral wall was observed for the hydropic ear, in whi ch normal ABR thresholds were maintained, as compared to the control ear. O n the contrary, a mild decrease in Ca2+-ATPase activity in the cochlear lat eral wall was observed for the hydropic ear, in which ABR thresholds increa sed significantly. The present findings suggest that alterations of Ca2+-AT Pase activity in the cochlear lateral wall may implicate disturbed calcium- homeostasis in the inner ear, resulting in hearing dysfunction in the early stages of experimentally induced endolymphatic hydrops. (C) 2001 Elsevier Science B.V. All rights reserved.