An ab initio Molecular Orbital Study on Effect of Electric Field Strength on Ionic Selectivity of the Sodium Channel

✍ Scribed by Katsuhiro Suenobu; Seiji Tani; Akira Imamura

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 268 KB
• Volume: 161
• Category: Article
• ISSN: 0022-5193
• DOI: 10.1006/jtbi.1993.1063

✦ Synopsis

The effect of electric field strength of the selectivity filter on ionic selectivity of the sodium channel has been studied by ab initio molecular orbital calculations. On the basis of the previous method, two kinds of model systems, the (\mathrm{FCO}{2} \mathrm{M}) system and the (\mathrm{FCO}{2} \mathrm{M}-\mathrm{H}{2} \mathrm{O}) system, were studied. In this study, a (\mathrm{FCO}{2}^{-})molecule, which is substituted for a (\mathrm{HCO}{2}^{-})molecule, was used as a model for the selectivity filter. This substitution corresponds to weakening the electric field strength of the selectivity filter. For this system, geometries of ground and transition states were optimized with MINI-3 basis sets. The (\mathrm{FCO}{2}-\mathrm{H}{2} \mathrm{O}) system, for which we evaluated thermochemical parameters and cross-sections, is a good model for ionic permeation of the sodium channel. When the results of the (\mathrm{FCO}{2} \mathrm{M}-\mathrm{H}{2} \mathrm{O}) system were compared with those of the (\mathrm{HCO}{2} \mathrm{M}-\mathrm{H}_{2} \mathrm{O}) system, we concluded that permeabilities of (\mathrm{Li}^{+})and (\mathrm{Na}^{+}) are smaller and that of (\mathrm{K}^{+})is larger as the field strength of the selectivity filter is weakened. Namely, the permeation of (\mathrm{K}^{+})is relatively favorable when the field strength of the selectivity filter is weakened. This conclusion is in accordance with the prediction of Eisenman's theory.