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-2+ ([K](e), [Na](e), [Cab) 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 +92 mV. [K](e), [Na](e), pH(e), and [Ca](e) were 169 mM, similar to 1.0 mM, 7.50, and 395 nM, respectively. In the Cldn14(-/-), the EP was +96 mV. [K](e), [Na](e), pH(e), and [Ca](e) were 167 mM, similar to 1.0 mM, 7.73, and 179 nM, 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(-/-). (C) 2017 Elsevier B.V. All rights reserved.