Development of monovalent ions in the endolymph in mouse cochlea

The present study was designed to clarify the chronological developmental p rocess of monovalent ions (Na+, K+, CI-) in the endolymph of the mouse in r elation to the development of the endocochlear potential (EP). The EP and i onic concentrations were measured simultaneously with the ion-sensitive dou ble-barreled microelectrodes from the scala media of the basal turn, The EP increased abruptly 7 days after birth (DAB) and reached approximately 80 m V 14 DAB, In the earliest postnatal days, the endolymphatic Na+ concentrati on was significantly higher than that in adult mice, however, the K+ and th e CI- concentrations were lower. The concentrations of all the monovalent i ons in endolymph reached adult levels at 7 DAB when the EP was still under 20 mV. These data strongly suggest the presence of a different mechanism be tween the production of monovalent ions, especially of high K+ in the endol ymph and that of EP. Copyright (C) 2000 S. Karger AG, Basel.