Characterization of the semi-intact mouse utricle preparation. (A) Illustration of utricle sensory epithelium showing the method of regional differentiation. Dimorphic terminals in the dark gray area were classified as central while dimorphic terminals in the light gray area were classified as peripheral. Arrows indicate bundle orientation around the line of polarity reversal. (B) Morphological characteristics were assayed through fluorescent imaging of Lucifer yellow–filled terminals. Bar, 10 µm. (C and D) We found no systematic differences in the number of calyces per terminal field (central: 2.6 ± 0.2, n = 13; peripheral: 2.8 ± 0.2; n = 14; C) or calyx width, measured from the external to the internal face juxtaposed the hair cell membrane (D) as a function of region. The number of samples is shown inside the bars for each condition. (E and F) Voltage steps between −124 mV and 96 mV in 10-mV increments elicited both inward Na⁺ and outward K⁺ currents. (G and H) I-V curves showed no differences in either steady-state K⁺ or peak Na⁺ currents as a function of location within the sensory epithelium. Space-clamp issues prevented further characterization of the large, fast K⁺ and Na⁺ currents but did not compromise characterization of the slower, smaller I_h in subsequent figures. Error bars indicate mean ± SEM.