XB-IMG-122080
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Figure 2. 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 V1/2 and effective charge q for each channel type were −41.7 ± 2.7 mV, 5.1 ± 1.1 e0 (SN, n = 3); −66.3 ± 3.4 mV, 7.5 ± 1.2 e0 (SNS, n = 6); −87.9 ± 1.9 mV, 9.2 ± 0.8 e0 (SNG, n = 3); −66.8 ± 2.8 mV, 10.7 ± 1.6 e0 (SS, n = 4). (D) Voltage dependence of the activation time constant τa, 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 δa obtained in the same fits as the time at which the extrapolated exponential crosses the current baseline. (F) Voltage dependence of deactivation time constants τd estimated by single-exponential fits. The apparent charge q was 0.80 e0 (SN), 0.96 e0 (SNS), 0.84 e0 (SNG), and 0.83 e0 (SS), as estimated by fitting the last five data points (lines) with the exponential function τ(V) = τ(0)exp(qV/kT). Image published in: Zheng J and Sigworth FJ (1997) Image reproduced on Xenbase with permission of the publisher and the copyright holder. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View |