State-dependent modification of the mutant channel E363A+T364C. cGMP-activated current traces at +60 mV in three different conformations of mutant channel: desensitized (A), closed (D), and open (E) states. (B) Effect of 5 mM DTT added to patch pipette solution in desensitized conformation of channel. (F and G) Effect of 2.5 mM MTSET added to the extracellular medium in closed (F) and open (G) states. 1 mM cGMP, 5 mM DTT, and 2.5 mM MTSET was added as indicated by the solid horizontal black or red bars. (C) Comparison of 5 mM DTT added to bath solution (red solid triangle), in patch pipette (red open square), and in DTT absence (black solid circle) in desensitized state; the values represent the amplitude of the peak current (I) measured every 30 s and normalized (I/Imax) to peak current of control (Imax) at time zero. (H) State-dependent modification in the closed (black solid circle) and open (black open circle) states in the absence of 2.5 mM MTSET, and in closed (red solid triangle) and open (red open triangle) states in the presence of 2.5 mM MTSET in the extracellular medium. Single points of the plots represent the amplitude of the peak current (I) measured every 5 s in open state and 30 s in closed state and, as in C, normalized (I/Imax) to peak current of control (Imax) at time zero.