A variety of computer-aided analyses was applied to the recently derived amino acid sequence of the Electrophorus electricus sodium channel protein in order to extract structural information such as hydrophobicity, periodicity, and secondary structure predictors. We propose a schematic model for the arrangement and folding of the polypeptide chain within the bilayer. The model consists of 4 homologous regions, each containing 8 membrane-spanning (probably a-helical) structures. Several. of these structures are amphipathic with a repeat of 3.5 residues, 4 of which (one from each homologous region) are postulated to form a negatively charged channel lining. Gating currents are proposed to arise from voltage-dependent separation of multiple ion pairs buried within the hydrophobic, intramembranous protein interior.

SUMMARY1. Extracellular recordings were made across the outer segment layer of isolated, superfused toad retinas. Under these recording conditions, the photovoltage reflects primarily the current flowing through the outer-segment membrane of red rods.2. In normal toad Ringer solution, a dim conditioning flash desensitized a test flash response. The desensitization reached a peak 1-8-2-0 s after the conditioning flash and then declined approximately as an exponential with time constant 6 s. 6. These results can be understood in terms of the Ca2+ hypothesis of transduction (Hagins & Yoshikami, 1974) if it is assumed that lowered [Ca2+]0 exposes an endogenous Ca2+ buffer. The data also provide evidence for a role of Na+/Ca2+ exchange in regulating intracellular Ca2+ concentration in the toad photoreceptor.7. A quantitative model based on these assumptions is derived and compared with the experimental data.