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Figure 2. The effect of external MTSET and MTSES on the wild-type, W1716C, F1764C, and W1716C/F1764C (WCFC) or W1716C/F1764R (WCFR) mutant channels. (A) The effect of external MTSET. (Left) The sample currents after 0- (black line), 60-, and 120-s (red lines) cumulative modification by MTSET are shown. The oocyte was initially held at −110 mV and stepped to −10 mV for 40 ms to elicit the control Na+ currents in ND-96 solution. The oocyte was then held at −35 mV and perfused with ND-96 containing 0.1 mM (for W1716C and WCFC mutant channels) or 1 mM (for wild-type and F1764C mutant channels) of freshly made MTSET for 30 s, after which the oocyte was held at −110 mV again and washed with control ND-96 for 30–60 s. The Na+ current after modification was assessed by a test pulse at −10 mV. This protocol was repeated until a steady state of MTSET modification was reached. We also repeated the same experimental protocols in the absence of MTS reagents and found no changes in the currents before and after the protocols (not depicted). (B) The relative currents are plotted against the cumulative time in MTSET (n = 3–4). The curves are relative current = 0.84 × exp(−t/36.2) + 0.16 and relative current = 0.22 × exp(−t/32.8) + 0.78 for the W1716C and WCFC mutant channels, respectively, where t denotes the cumulative time in MTSET in seconds. (C) Peak Na+ currents after 90-s MTSET modification is normalized to control currents to give the relative currents (n = 3–4). (D) The effect of external MTSES. The oocyte was held at −120 mV, perfused with control ND-96 solution or ND-96 solution containing 2 mM of freshly made MTSES, and stepped every 2 s to −10 mV for 100 ms to assess the Na+ currents. A steady-state effect of MTSES is usually reached within 40 s in these mutant channels (not depicted). The oocyte was then washed with control ND-96 for 30–60 s and stepped to −10 mV to measure the Na+ current. The Na+ currents after 0- (black line) and 40-s (red line) cumulative modification by MTSES are superimposed. (E) Peak Na+ currents after a 40-s MTSES modification are normalized to control currents to give the relative currents (n = 3–4). Image published in: Yang YC et al. (2009) © 2009 Yang et al. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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