Figure 3.

Coupling of the nAChR current to the activation of SK channels. A, Representative recordings of the currents evoked by ACh in IHCs at P3 and P13, voltage-clamped at the holding potentials indicated under each record. In all cases the intracellular solution contained KCl and EGTA. Notice that currents were inward at -90 mV and outward at -50 mV, indicating that SK potassium currents were present. Illustrated records are representative of those found in three to six different IHCs at each age. B, Representative traces of K⁺-evoked combined nAChR plus SK IPSCs at P9-P11 by 40 mm K⁺ (E_K, -35 mV). C, Representative traces of K⁺-evoked isolated nAChR synaptic currents at P9-P11 by 40 mm K⁺ (E_K, -35 mV). D, Representative records of one combined (nAChR + SK) IPSC (gray trace) and one isolated (nAChR) postsynaptic current (black trace) superimposed to illustrate the much slower kinetics of the combined nAChR plus SK IPSC. E, bar diagrams showing that combined nAChR plus SK IPSCs have a larger amplitude and slower kinetics than those of the isolated nAChR postsynaptic currents (p < 0.0001). In B, recordings were made with a KCl-EGTA intracellular solution; in C, recordings were made with an intracellular solution in which EGTA was replaced by BAPTA to prevent the activation of SK channels. Recordings in B-D were made at a V_hold of -90 mV.