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Figure 4. Steady-state slow and fast inactivation in high and low [Na+]o. Steady-state slow inactivation (SΘ) curves for F1485Q (A) and WT hH1a (B). Transfected cells were held at holding potentials ranging from −160 to −30 mV in 10- or 20-mV increments. After 2 min at each holding potential, a 20-ms recovery pulse to −140 mV and a 9-ms test pulse to +60 mV were given (insets). The peak current measured at +60 mV is plotted as a fraction of the maximal current. (A) F1485Q SΘ curves. The data points are fit to the Boltzmann equation (solid lines) with midpoints at −79.0 ± 1.1 and −85.9 ± 1.7 mV and slope factors of 6.9 ± 0.4 and 6.0 ± 0.6 mV for 150 and 10 mM external Na+, respectively (n = 4 cells for 150 mM Na+ and n = 5 cells for 10 mM Na+). (B) WT SΘ curves. Best-fits to the Boltzmann equation have midpoints at −82.2 ± 2.8 and −102.0 ± 0.5 mV and slope factors of 25.4 ± 2.5 and 15.3 ± 0.6 for 150 and 0 mM Na+o, respectively (n = 3 cells for each [Na+]o). (C and D) Steady-state fast inactivation (hΘ) induced by a 50-ms prepulse to the indicated voltage from a holding potential of −160 mV (see insets). Test pulse, +60 mV. The peak current at +60 mV is plotted as a fraction of the maximal current. (C) F1485Q hΘ curves. Data shown are from 3 cells sequentially bathed in 150, 10, and 150 mM Na+. The best-fit Boltzmann curves have midpoints at −73.8 ± 2.4, −78.0 ± 2.6, and −75.6 ± 3.0 mV and slope factors of 3.27 ± 0.16, 3.47 ± 0.35, and 3.53 ± 0.36 mV for 150, 10, and 150 mM Na+o, respectively. (D) WT hΘ curves. Data from 3 cells transfected with WT hH1a and successively bathed in 150, 0, and 150 mM Na+. Inactivation curves are fitted to the Boltzmann equation with midpoints at −100.3 ± 0.9, −103.4 ± 0.6, and −103.5 ± 0.4 mV and slope factors of 8.0 ± 0.2, 8.8 ± 0.3, and 7.8 ± 0.2 for 150, 0, and 150 mM Na+o, respectively. In each panel, the dashed lines are the Boltzmann curves for 10 (F1485Q) or 0 mM Na+o (WT) multiplied by 0.67 (F1485Q) or 0.84 (WT), giving the expected reduction in Popen for the decrease in [Na+]o (Townsend et al., 1997). Image published in: Townsend C and Horn R (1997) Image reproduced on Xenbase with permission of the publisher and the copyright holder. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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