Figure 5.

The double mutant channel F317C_Y347C is locked in the open state. (A,B) Mapping CNGA1 residues on TAX-4 structure reveals the presence of hydrophobic interactions. (C) Enlargement of panels a and b illustrating the network of H-bonds and hydrophobic π-interactions. (D) left: current recordings obtained in the absence of cGMP (0 cGMP) for mutant channels F317C_Y347C, elicited by voltage steps from −200 to +200 mV (ΔV = 20 mV); right: after the addition of 1 mM cGMP. (E) left: current recordings obtained in the absence of cGMP; right: 1 minute after the addition of 1 µM dequalinium. (F,G) Current recordings obtained in the absence of cGMP following subtraction of those currents recorded in the presence of dequalinium (F) or after P/-4 procedure for leak and capacitive artefact subtraction (G). (H) Dependence of G/Gmax on V with 1 µM dequalinium and in the absence of cGMP (n = 4, black) and in the presence of 1 mM cGMP (n = 3, red). (I) single channel recordings obtained in the absence of cGMP for mutant channels F317C_Y347C, elicited at different voltages. Amplitude histograms are shown at the right of each trace. isc, single-channel current amplitude. (K) current recordings obtained from the WT CNGA1 channels in the presence of 1 mM cGMP, elicited by the same voltage steps as in (D). (L) Dependence of G/Gmax on V obtained from the recordings of WT CNGA1 channels (K) in the presence (n = 1) of DMA.