Ion selectivity predictions from a two-site permeation model for the cyclic nucleotide-gated channel of retinal rod cells

The model predicts that Ca2+ and Mg2+ contribute 21% and 10% of the total current in retinal rod cells at -60 mV.

• A two-site, Eyring rate theory model was developed for ionic permeation in cyclic nucleotide-gated channels.
• The model effectively represented the shape of current-voltage relations and binding affinity for Na+.
• Predicted reversal potential values matched experimental data for Ca2+ or Mg2+ additions and biionic KCl.
• Differences in predicted extracellular block values for Ca2+ and Mg2+ suggest that the beta-subunit or a cell-specific factor influences divalent cation interactions externally.
• The model indicates concentration-dependent permeability ratios and anomalous mole fraction effects for both monovalent and divalent cations.

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