Figure 4: Electrophysiological properties of organoid hair cells.

(a) Families of outward K⁺ currents evoked by the voltage protocol shown below. (b) Mean±s.e.m. peak current–voltage relations for 27 organoid hair cells (D22–28) and eight Type II utricle hair cells (P4). (c) Mean±s.e.m. time constants of single exponential fits to K⁺ current activation as function of membrane potential for D22–25 (n=12), D26–28 (n=6) organoid hair cells and P4 utricle hair cells (n=7). (d) Families of K⁺ current evoked by a voltage protocol (below) with a prepulse to −125 mV. (e) A family of fast inward rectifier currents recorded from a D23 organoid hair cell evoked by the protocol shown below. (f) Mean±s.e.m. peak inward rectifier current–voltage relations for 27 organoid hair cells and eight utricle hair cells. (g) Families of Na⁺ current activation (left) and inactivation (right). (h) The voltage dependence of Na⁺ current inactivation extracted from the peak inward currents (panel g, right) plotted as a function of prepulse potential and fit by a Boltzmann curve with V_1/2inact=−78.3 mV and s=5.9 mV. (i) Prevalence of Na⁺ current in organoid hair cells as a function of days in culture. Total number of cells for each age is indicated above the bars. (j) A family of slow hyperpolarization-activated currents (I_h) evoked by the protocol below. (k) Prevalence of I_h in organoid hair cells as function of days in culture. Number of cells is indicated above each bar. (l) Representative membrane responses of utricle and organoid hair cells to step current injections (below). (m) A family of voltage responses evoked by incremental current steps. (n) Representative utricle and organoid hair cell membrane responses to sinusoidal current injections.