Covalent modifications by MTS reagents alter the single-channel conductance. (A and B) Single-channel recordings at −50 mV show that application of MTSET⁺ increases unitary current amplitudes for cysless/N1148C (A) or cysless/W1145C (B). Linear fits to single-channel current measurements at different voltages yield unitary conductance values for cysless/N1148C (A) of 7.1 pS before (black) and 9.2 pS after (blue) MTSET⁺ treatment, for cysless/W1145C (B) of 7.6 pS before (black) and 10.1 pS after (blue) MTSET⁺ treatment. (C and D) Single-channel recordings show that the unitary current amplitude decreases after MTSET⁺ (C; blue) or MTSACE (D; green) exposure for cysless/S1141C. Linear fits to single-channel current measurements at different voltages yield unitary conductance values for cysless/S1141C of 7.0 pS before (C and D; black) and 6.1 pS after both MTSET⁺ (C; blue) and MTSACE (D; green) treatment. Each data point is the average of three to six patches. Symbols are larger than SEM.