Conductance selectivity of Na ⁺ across the K ⁺ channel via Na ⁺ trapped in a tortuous trajectory

Abstract

Significance Ion selectivity is a fundamental property of ion channels. Potassium channels exhibit an unusual selectivity, allowing passage of larger K + ions (ionic radius of 1.3 Å) over smaller Na + ions (1.0 Å); the mechanism underlying the small ion rejecting selectivity remains unknown. Here, we applied Na + as a probe for examining the pore of a prototypical potassium channel and found slight Na + conduction across the pore. Na + traced a tortuous trajectory in the narrow pore, with multiple Na + ions trapped here and there, leading to slow elution. Contrarily, K + passed straight, with three ions moving together rapidly. Na + and K + take different paths and interactions in the pore, which creates dramatic contrast in the conduction rates of Na + and K + .

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