Macroscopic currents from cell-attached patch recordings of the various channel types. (*A*) Activation currents were induced by depolarizing pulses from a −100-mV holding potential to potentials of: −50 to 100 mV (SN); −80 to 100 mV (SNS); −80 to 30 mV (SNG); and −80 to 60 mV (SS); all in steps of 10 mV except 20 mV for SNS. The post pulse was −140 mV. (*B*) Tail currents were recorded at voltages of −70 to −150 mV (SN) and −110 to −170 mV (SNS, SNG, and SS) after prepulses to 40 mV (SN) or 0 mV (SNS, SNG, and SS). Potassium ion concentration was 140 mM on each side of the patch. Currents were filtered at 1 kHz. Note the different time scale for SN currents. (*C*) Representative *G*-*V* curves for each channel type, calculated from the macroscopic currents assuming a linear *I* -*V* relationship. Superimposed on each curve is a fit of a Boltzmann function. The midpoint voltage *V*_{1/2} and effective charge *q* for each channel type were −41.7 ± 2.7 mV, 5.1 ± 1.1 e_{0} (SN, *n* = 3); −66.3 ± 3.4 mV, 7.5 ± 1.2 e_{0} (SNS, *n* = 6); −87.9 ± 1.9 mV, 9.2 ± 0.8 e_{0} (SNG, *n* = 3); −66.8 ± 2.8 mV, 10.7 ± 1.6 e_{0} (SS, *n* = 4). (*D*) Voltage dependence of the activation time constant τ_{a}, estimated by fits of an exponential function to the activation time course, starting from the time when the amplitude is 50% of the final value. (*E*) Voltage dependence of the activation delay time δ_{a} obtained in the same fits as the time at which the extrapolated exponential crosses the current baseline. (*F*) Voltage dependence of deactivation time constants τ_{d} estimated by single-exponential fits. The apparent charge *q* was 0.80 e_{0} (SN), 0.96 e_{0} (SNS), 0.84 e_{0} (SNG), and 0.83 e_{0} (SS), as estimated by fitting the last five data points (*lines*) with the exponential function τ(*V*) = τ(0)exp(*qV*/*kT*).

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