Xenbase Image ID: 121547

Figure 2. Na+ ions gate GIRK channels after activation by G protein βγ subunits. (A) Single-channel activity (NPo, bin = 5 s) plotted as a function of time. The data were obtained from an inside-out patch excised from an oocyte expressing the recombinant channel GIRK1/GIRK4. 20 mM Na+ and 10 μM GTPγS were applied as indicated by the bars. The membrane was clamped at −80 mV and 5 μM acetylcholine was in the pipette solution. (B) The mean NPo for seven patches is plotted for different conditions. Steady state channel activity after activation by GTPγS was taken as reference (GTPγS) and NPo were normalized to it. Na+ concentration was 20 mM and GTPγS was 10 μM. GTPγS+Na+ corresponds to the application of 20 mM Na+ after the washout of the GTP analogue. SEM are indicated by the vertical bars. The normalized mean NPo was 0.057 ± 0.018 (mean ± SEM) in control solution, 0.277 ± 0.095 in the presence of 20 mM Na+ ions, 1 after the application of 10 μM GTPγS, and 4.21 ± 0.59 in the presence of 20 mM Na+ ions after channel activation by GTPγS. (C) NPo vs. time plot for the channel activity recorded in an inside-out patch from an oocyte expressing GIRK1/GIRK4. 20 mM Na+ and 20 nM β1γ7 purified subunits were applied via the bath as indicated by the bars. Vm = −80 mV. 5 μM acetylcholine was present in the pipette. (D) The mean NPo for nine patches are plotted for different conditions. Steady state channel activity after β1γ7 activation (after β1γ7 washout) was taken as reference and NPo was normalized to it. Na+ concentration was 20 mM and β1γ7 was 20 nM. βγ+Na+ refers to the application of 20 mM Na+ after the washout of βγ. The vertical bars represent SEM. The normalized mean NPo was 0.084 ± 0.039 (mean ± SEM) in control solution, 0.206 ± 0.12 in the presence of 20 mM Na+ ions, 1 after the application of 20 nM β1γ7, and 3.1 ± 0.84 in the presence of 20 mM Na+ ions after activation of the channel by the G protein subunits. Image published in: Petit-Jacques J et al. (1999) © 1999 The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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