Molecular determinants of external barium block in Shaker potassium channels

Abstract

Mutations in the outer pore region of Shaker K⁺ channels (^T449 and D⁴⁴⁷) can influence external Ba²⁺ block. Substitution of T⁴⁴⁹ by A, V or Y differentially reduced Ba²⁺ block primarily by decreasing the blocking rate. Substitution of D⁴⁴⁷ by N resulted in a non‐conducting channel with apparently normal gating currents. External Ba²⁺ can speed the OFF gating current of a different non‐conducting mutant, W434F; this effect was markedly attenuated by the D447N substitution. These results suggest that D⁴⁴⁷ contributes to an external Ba²⁺ binding site while T⁴⁴⁹ imposes a barrier to the access of that site.