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. 2007 Apr;129(4):345–350. doi: 10.1085/jgp.200709757

Figure 3.

Figure 3.

E79 accessibility is state dependent. (A) Normalized wild-type currents (WT) and E79C current before (E79C) or after (E79C + MTSES) exposure to 1 mM MTSES for 5 min at pH 8.0. (B) E79C currents before (NA) and after exposure to 1 mM MTSES for 5 min at the indicated pH. Inset shows steady-state desensitization for E79C (pH0.5 of 7.91, n = 9); at pH 7.0, channels are fully desensitized. Currents were fit with a double exponential with fast (∼120 ms) and slow (>600 ms) components. Histograms (C) give the percentage of the current that was fit with a slow time constant against the pH of the MTS incubation solution. (D) MTSES sensitivity depends on desensitization, not pH itself. Cells were exposed to 1 mM MTSES for 5 min at pH 8.0 or pH 7.2 in 1 mM Ca2+, or pH 7.2 in 20 mM Ca2+. The addition of 20 mM Ca2+ shifts the steady-state desensitization curve (hollow circles, inset) so channels are available to open at pH 7.2, thereby rendering them sensitive to MTSES.