Reversibility by reduction of the functional effects of cross-linking. (A) Normalized conductance as a function of voltage for pWT-HRV before (unfilled circles) and after (filled circles) 20 mM DTT (pH 8.0) for 5 min. The measurements were made in outside-out macropatches with 10 μM Ca²⁺ inside the pipet. G-V curves were determined before and after DTT on the same patch. Similarly, G-V curves were determined before and after DTT for (B) R17C–P137C, (C) R20C–F144C, and (D) R20C–R201C. (E) V₅₀ (±SD and n) for pWT-HRV and the three double-Cys mutants, before and after DTT.