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

Objective: 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 Ca ([K], [Na], pH, [Ca]) in Cldn14, in which hair cells were selectively damaged, and compared with measurements in wild type mice (Wt).

Methods: 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], [Na], pH, and [Ca] in both Wt and Cldn14 at 8-10 weeks of age.

Results: (1) In Wt, the EP was +92mV. [K], [Na], pH, and [Ca] were 169mM, ∼1.0mM, 7.50, and 395nM, respectively. In the Cldn14, the EP was +96mV. [K], [Na], pH, and [Ca] 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] (R=0.93) was observed for both Wt and Cldn14, but no correlation was observed between EP and K, Na, or H.

Conclusion: These findings suggest that (1) the changes in endolymphatic ion concentrations might not be involved in hair cells degeneration in Cldn14, (2) [Ca] might be regulated by EP in both Wt and Cldn14.