Permeability to chloride ions of the cochlear partition in normal guinea pigs

The endocochlear potential and Cl- activities in the endolymph and perilymph of guinea pigs were simultaneously measured with a pair of double-barreled Cl--sensitive liquid-membrane electrodes. Under normal conditions the mean Cl- activity was 96.6 mEg/l in the endolymph and 93.5 mEq/l in the perilymph. The mean Cl- concentration determined by potentiometric titration was 132.3 mM in the endolymph and 121.8 mM in the perilymph. The permeability to Cl- of the cochlear partition was determined after active transport was abolished by permanent anoxia. The modified permeability coefficient and conductance for Cl- of the cochlear partition were computed from the rate of decrease in the Cl- concentration of the endolymph and its electrochemical potential difference between the endolymph and perilymph. The mean modified Cl- conductance and permeability coefficient of the cochlear partition were (10.7 +/- 4.25) X 10(-3) omega -1 . cm-3 and (22.58 +/- 8.95) X 10(-6) s-1 respectively, when averaged from 10 to 30 min after onset of anoxia. Our results indicate that the cochlear partition is relatively permeable to Cl-, when compared to its permeability to K+. Possible coupling between Cl- and water movement across the cochlear partition is discussed.