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

Abstract 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 , 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 +92 mV. [K] e , [Na] e , pH e , and [Ca] e were 169 mM, ∼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, ∼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 −/− .