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 Ca²⁺ ([K]_e, [Na]_e, pH_e, [Ca]_e) 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]_e, [Na]_e, pH_e, and [Ca]_e in both Wt and Cldn14^-/- at 8-10 weeks of age. RESULTS:(1) In Wt, the EP was +92mV. [K]_e, [Na]_e, pH_e, and [Ca]_e were 169mM, ∼1.0mM, 7.50, and 395nM, respectively. In the Cldn14^-/-, the EP was +96mV. [K]_e, [Na]_e, pH_e, 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⁺. CONCLUSION: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^-/-.

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