Figure 10. UV sensitivity and gating properties of CNG channels lacking a conserved pore tryptophan residue. (A and B) UV dose–response relations in saturating (1 mM) cGMP for OLF channels (open symbols, A and B, seven experiments), OLF/W332Y mutant channels (solid symbols, A, eight experiments), and OLF/W332H mutant channels (solid symbols, B, five experiments). Results from experiments on each type of channel were shifted along the abscissa as in Fig. 3 A. Different symbols represent separate experiments. Continuous curves are fits to the pooled results for each construct using . D1/2 values and slope factors from the fits are given in Table . Patches were irradiated with 280 nm UV in the absence of cGMP. (C) Cyclic GMP dose–response relations for OLF channels (open symbols, six experiments) and OLF/W332Y mutant channels (solid symbols, six experiments) before irradiation. The cGMP-activated current, I, divided by the maximal current in 1 mM cGMP, Imax, is plotted as a function of cGMP concentration on double logarithmic axes. Results from each experiment were shifted along the abscissa so that the half-saturating ligand concentration, K1/2, was equal to the average value of K1/2 for all experiments on the same channel. Different symbols represent separate experiments. Continuous curves are fits to the pooled results for each type of channel using the Hill equation (). The fitting parameters were: for OLF channels, h = 2.35 and K1/2 = 2.47 μM; for OLF/W332Y channels, h = 2.17 and K1/2 = 17.7 μM. (D) Relative efficacies of cAMP and cGMP for activating wild-type OLF, OLF/W332Y mutant, and OLF/W332H mutant channels. Ordinate is the ratio of the current amplitude in saturating cAMP (>3 mM) to that in saturating cGMP (1 mM). The current ratios, (mean ± SEM) and the number of experiments (in parentheses) were: for OLF, 1.01 ± 0.02 (4); for OLF/W332Y, 0.30 ± 0.05 (8); and for OLF/W332H, 0.45 ± 0.11 (5).
Image published in: Middendorf TR and Aldrich RW (2000)
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