Figure 4.
Acquisition of the low-voltage-activated conductance, GK,L, at approximately E18. A, A representative family of currents recorded from a putative type I hair cell. The voltage protocol (below) was identical to that used to evoke the currents in Figure 3. The dashed line shows the zero-current level. B, A hyperpolarizing prepulse to -124 mV deactivated the currents that were active at rest. A subsequent family of depolarizations (bottom traces) was used to reactivate the currents. Same cell as in A. Fits of Equation 1 are superimposed on the three middle traces (gray lines). The dashed line indicates the zero-current level. C, Activation curves derived from the data shown in B (open circles) and, for comparison, from the delayed rectifier conductance of a typical E18 hair cell (filled circles). Both datasets were fit with Boltzmann equations with a V1/2 of -66 and -28 mV, an s of 6.8 and 5.6 mV, and a GMax of 34 and 16 nS, respectively. D, Bar graph of mean maximum chord conductance for GK,L at each developmental stage. Only cells with GK,L were included in the mean. Error bars show SD. The fraction indicates the number of cells with GK,L over the number of cells studied at each stage. Note that the study was not done blind and that we sometimes targeted cells with type I morphological features. Therefore, the ratios do not represent the proportion of type I cells in the developing utricular epithelium.