XB-IMG-121906
Xenbase Image ID: 121906
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Figure 1. Gating currents from oocytes expressing the truncated and full-length forms of the rabbit skeletal muscle L-type Ca2+ channel α1 subunit (α1SÎC and α1S). (A) Voltage-clamp traces recorded in six oocytes during 20-ms depolarizing steps to the values shown on the left from a holding potential of â90 mV. The combination of cRNAs injected is shown above each set of traces. Each trace is the average of four responses filtered at 1 kHz and sampled at 20 kHz. The dotted lines represent zero current. (B) Qon vs. âQoff plot for the α1SÎC, β1b-injected oocyte from A, middle right, shows charge conservation. A straight line with a slope of 1 is shown as a reference. Values of Qon and Qoff were obtained by integrating the gating currents during and after the pulse. 10 datum points (0.5 ms) near the end of the pulse were used to define the baseline for Qon, while 10 datum points near the end of the trace (3â5 ms after the end of the pulse) were used to define the baseline for Qoff. Qon was integrated throughout the pulse to allow slow components of charge movement to be included. Qoff did not have prominent slow components and was integrated over the first â¼3 ms after the pulse. A number of cells showed small, slow tail currents at depolarized potentials (see +20 mV traces in A, top right and middle left) that were excluded from Qoff by baseline subtraction. (C) Qon (â¢) and Qoff (â¾) versus voltage for the same oocyte were fitted by Boltzmann distributions of the form: Q-V = Qmax/{1 + exp[â(V â V1/2Q)/kQ]}, where Qmax is the maximal charge moved at depolarized voltages, V1/2Q is the voltage at which charge movement is half maximal, and kQ describes the steepness of the distribution. The solid line shows the average of the Qon and Qoff fits: Qmax = 175 pC, V1/2Q = â25.9 mV, and kQ = 15.6 mV. Image published in: Morrill JA and Cannon SC (2000) © 2000 The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View |