Quaternary ammonium ions can externally block voltage-gated K+ channels.: Establishing a theoretical and experimental model that predicts KDs and the selectivity of K+ over Na+ ions

The physicochemical basis for the high ion selectivity of potassium channels is poorly understood. In the present studies, external blockade of cloned voltage-gated potassium channels with alkyl quaternary ammonium ions are analyzed from a model derived from theory and experimental data. Atomic mass units, electrostatic potential residing on the nitrogen atom, the COSMO van der Waals solvent accessible surface, the Onsager solvation model, and the isodensity PCM solvation model are computed at the semi-empirical and the ab initio levels of theory. A structure-activity relationship (SAR) exists between the calculated values and the experimentally obtained K-D (mM). The SAR model gives us K-D predictions and when K+ and Na+ are incorporated into the model, it dramatically predicts the selectivity of K+ over Na+ ions. (C) 2001 Elsevier Science B.V. All rights reserved.