4QE7:
reference: Ionic interactions of Ba2+ blockades in the MthK K+ channel., Guo R, Zeng W, Cui H, Chen L, Ye S, J Gen Physiol. 2014 Aug;144(2):193-200. doi: 10.1085/jgp.201411192. Epub 2014 Jul, 14. PMID: 25024268

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