XB-IMG-120250
Xenbase Image ID: 120250
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Figure 2. . Voltage clamp protocols and data analysis for the characterization of channel function using wild-type (WT) HERG as an example. (A) Voltage dependence of activation. Top inset: voltage clamp protocol. Bottom inset: representative original current traces elicited by the protocol. The gray shade highlights the peak of tail currents that is used to estimate the degree of channel activation. The main graph depicts summary activation curve calculated from Eq. 1, V0.5 = −13.6 ± 1.3 mV and zg = 2.70 ± 0.07. (B) Time constant of activation (τo) and its voltage dependence. Top inset: “envelope test” protocol. Bottom inset: representative original current traces elicited by the envelope test protocol at a Vt of +20 mV. The solid curve superimposed on the current traces is calculated from Eq. 3, with tdelay = 1.7 ms and τo = 97 ms. The main graph depicts summary data plotted on a semilogarithmic scale, superimposed on a line calculated from Eq. 4. The value of zo is obtained by a linear regression analysis of relationship between ln(Ko(V)) and Vt in the Vt range of −40 to +40 mV (0.83). (C) Fully-activated current-voltage (If-a-V) relationship. Top inset: voltage clamp protocol. Bottom inset: original current traces elicited by the protocol. The gray shade highlights the peak tail current amplitudes used to construct the If-a-V curve. The main graph depicts the average If-a-V relationship. (D) Time constant of the fast component of deactivation. The protocol is the same as that in C. Inset: original data (open circles, showing only every twentieth data points) and fitting result (superimposed solid curves) at Vr −80 and −120 mV. The main graph reports τc values plotted on a semilogarithmic scale. (E) Voltage clamp protocol and curve fitting to estimate the time constant of inactivation (τI). The main graph depicts current traces (plotted every twentieth data points) recorded during the second and third pulses (shaded portion of the protocol), superimposed with one-exponential fit to the decay phase during the third pulse. (F) Summary data of τI values from −20 to +40 mV. Data shown in the main graphs are summarized from 3–11 cells each. These WT data are shown again as open triangles in Figs. 3–6 and 8, as a comparison with data from mutant channels. Calibration bars correspond to 1 μA and 0.2 s, except those in E (5 μA and 10 ms). Image published in: Liu J et al. (2003) Copyright © 2003, The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View |