Measurements of ionic concentrations along with endocochlear potential in wild-type and claudin 14 knockout mice

To examine whether the changes in endolymphatic ion concentrations were involved in hair cells degeneration in claudin-14 knockout (KO) mice (Cldn14−/−), we measured the endocochlear potential (EP) along with concentrations of K+, Na+, H+, or Ca2+ ([K]e, [Na]e, pHe, [Ca]e) in Cldn14−/−, in which hair cells were selectively damaged, and compared with measurements in wild type mice (Wt). We used the Cldn14−/− from 3 weeks of age, in which the auditory brain responses (ABR) was severely diminished. Using double-barreled ion-selective microelectrodes, we measured [K]e, [Na]e, pHe, and [Ca]e in both Wt and Cldn14−/− at 8–10 weeks of age. (1) In Wt, the EP was +92mV. [K]e, [Na]e, pHe, and [Ca]e were 169mM, ∼1.0mM, 7.50, and 395nM, respectively. In the Cldn14−/−, the EP was +96mV. [K]e, [Na]e, pHe, and [Ca]e were 167mM, ∼1.0mM, 7.73, and 179nM, respectively. No significant differences in the above values were observed between Wt and Cldn14−/−. (2) A significant linear correlation between EP and [Ca]e (R=0.93) was observed for both Wt and Cldn14−/−, but no correlation was observed between EP and K+, Na+, or H+. These findings suggest that (1) the changes in endolymphatic ion concentrations might not be involved in hair cells degeneration in Cldn14−/−, (2) [Ca]e might be regulated by EP in both Wt and Cldn14−/−.