In situ electrophysiology
Animals were anesthetized with inactin (thiobutabarbital sodium salt, 140 mg/kg ip). The endocochlear potential and the endolymphatic [K+] were measured with double-barreled microelectrodes [17]. Measurements were made in the basal turn by a round-window approach through the basilar membrane and in the apical turn after thinning the bone over the stria vascularis and picking a small hole (~30 μm). K+-selective electrodes were calibrated in solutions of constant cation (K+ and Na+) concentration of 150 mM. The minor selectivity of the K+ electrodes for Na+ produced a nonlinearity in the calibration curve, which was closely fitted by the Nicolski equation using nonlinear curve-fitting software (OriginLab, Northampton, MA): V = Vi + S × log ([K+] + A × [Na+]), where Vi is an offset term, S is slope, A is selectivity, and [Na+] is Na+ concentration. Calibrations were made immediately after withdrawal of the electrodes from the cochlea. Plasma K+ concentrations were obtained using a blood analyzer (Stat Profile M, Nova Biomedical, Waltham, MA).
Data are presented as mean ± sem; n denotes the number of experiments. Differences were considered significant when p < 0.05.