XB-IMG-118342
Xenbase Image ID: 118342
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Figure 1. Intracellular Mg2+ blocks both WT and mutant (E321N/E324N) channels in a voltage- and concentration-dependent manner. A and B present ribbon structures of MthK for a side view of two opposed subunits and for a bottom view looking from the cytoplasm toward the channel for all four subunits, obtained with Swiss Protein Viewer and coordinates from Jiang et al. (2002a). The negatively charged residues E321 and E324 in BK channels are projected onto the ribbon structures as space filling structures (red and blue), which are substituted for E92 and L95 in MthK. Brelidze et al. (2003) substituted for R93 and E96 in their Fig. 1. It is unclear which substitution would be closer to the unknown structure of the BK channel. (C) Representative single-channel currents recorded from WT (top traces) and E321N/E324N (lower traces) BK channels expressed in oocytes with symmetrical 150 mM KCl and the indicated Mg2+i concentration. Membrane potential: +100 mV. Effective filtering: 5 kHz. Channel opening indicated by upward going currents. (D and E) Plots of outward unitary current amplitude versus voltage at the indicated Mg2+ from WT (filled symbols) and mutant (open symbols) channels, respectively. The intracellular solutions for all figures before adding the blocking ions or increasing intracellular KCl were (in mM) 150 KCl, 5 TES, 1 EGTA, 1 HEDTA, pH 7.0. The lines are descriptions with Eq. 5 for simultaneous fitting of the data in D for WT channels: KBap(0) for Mg2+i = 48.3 ± 3.0 mM, d = 0.25 ± 0.01, and n = 0.64 ± 0.01, and simultaneous fitting of the data in E for E321N/E324N channels: KBap(0) for Mg2+i = 143 ± 16.6 mM, d = 0.19 ± 0.01, and n = 0.61 ± 0.02. Image published in: Zhang Y et al. (2006) Copyright © 2006, The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View |