Larger Image Figure 2. Injection of a mixture of WT and E333G CNG subunits gives rise to six types of channel behavior. (A) In addition to WT behavior (showing three distinct nonzero conductance states of 65–70, 35–40, and 15–20 pS; bottom) and pure mutant behavior (showing one nonzero conductance state of ∼25 pS; top), four hybrid types of CNG channel behavior were recorded and named Types A, B, C, and D. (Left and middle) For each channel type, a single-channel current record obtained at a holding potential of −80 mV with 130 mM NaCl, pH 7.6, on both sides of the membrane is shown alongside a corresponding amplitude histogram. Type A channels had noisy openings and gave an amplitude histogram with a low-conductance (∼31 pS) peak and a long high-conductance tail. Type B channels showed two distinct conductance states of ∼50–65 and ∼25–40 pS. Type C channels fluctuated widely about a conductance level of ∼55 pS, giving an amplitude histogram with one broad peak and tails extending to both low and high conductances. The single-channel behavior of Type D channels looked similar to WT behavior, although the Type D amplitude histogram calculated from many openings had two broad peaks (∼70–75 and ∼25–30 pS) rather than the three sharper peaks typical of WT channels. (Right) Average amplitude histograms calculated from all the histograms assigned to each category (pure mutant, A, B, C, D, and WT). For each hybrid channel, the group average histogram is similar to the individual example shown in the middle column, suggesting that the behavior of each of the hybrid channel types was unique. (B) Of 65 single channels recorded in patches from oocytes injected with a 2:1 mixture of WT and E333G CNG subunits, 6 mutant, 2 WT, and 57 hybrid channels were observed. Of the hybrid channels, Type A \documentclass[10pt]{article} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{pmc} \usepackage[Euler]{upgreek} \pagestyle{empty} \oddsidemargin -1.0in \begin{document} \begin{equation*}(n\;=\;20)\end{equation*}\end{document} and Type B \documentclass[10pt]{article} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{pmc} \usepackage[Euler]{upgreek} \pagestyle{empty} \oddsidemargin -1.0in \begin{document} \begin{equation*}(n\;=\;21)\end{equation*}\end{document} channels were found roughly twice as frequently as Types C and D channels \documentclass[10pt]{article} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{pmc} \usepackage[Euler]{upgreek} \pagestyle{empty} \oddsidemargin -1.0in \begin{document} \begin{equation*}(n\;=\;8\;{\mathrm{for\;both}})\end{equation*}\end{document}. Image published in: Morrill JA and MacKinnon R (1999) © 1999 The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Permanent Image Page Printer Friendly View XB-IMG-121462