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A residue in the intracellular vestibule of the pore is critical for gating and permeation in Ca²⁺-activated K⁺ (BK_Ca) channels

J. D. Lippiat, N. B. Standen and N. W. Davies

1. We have used patch clamp to record large-conductance Ca²⁺-activated K⁺ (BK_Ca) currents from a human embryonic kidney cell line (HEK293) expressing wild-type and mutant hSlo channels.

2. When we mutated F380 in the S6 region, thought to contribute to the intracellular vestibule of the pore, to isoleucine (F380I), very little channel activity was recorded. In contrast, mutation to tyrosine (F380Y) resulted in significant voltage-dependent currents.

3. The unitary conductances of F380I, F380Y and wild-type channels were 92 ± 6 pS (n = 3), 166 ± 5 pS (n = 3) and 294 ± 5 pS (n = 5), respectively.

4. Both mutant and wild-type hSlo channels were sensitive to 100 nM iberiotoxin.

5. The F380Y mutant produced channels that were active at negative membrane potentials, even in the absence of Ca²⁺.

6. We conclude that this conserved residue within BK_Ca channels may line the conduction pathway and forms a key element of the gating mechanism.

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