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. 1999 Jun;76(6):3141–3149. doi: 10.1016/S0006-3495(99)77465-5

Batrachotoxin-resistant Na+ channels derived from point mutations in transmembrane segment D4-S6.

S Y Wang 1, G K Wang 1
PMCID: PMC1300282  PMID: 10354438

Abstract

Local anesthetics (LAs) block voltage-gated Na+ channels in excitable cells, whereas batrachotoxin (BTX) keeps these channels open persistently. Previous work delimited the LA receptor within the D4-S6 segment of the Na+ channel alpha-subunit, whereas the putative BTX receptor was found within the D1-S6. We mutated residues at D4-S6 critical for LA binding to determine whether such mutations modulate the BTX phenotype in rat skeletal muscle Na+ channels (mu1/rSkm1). We show that mu1-F1579K and mu1-N1584K channels become completely resistant to 5 microM BTX. In contrast, mu1-Y1586K channels remain BTX-sensitive; their fast and slow inactivation is eliminated by BTX after repetitive depolarization. Furthermore, we demonstrate that cocaine elicits a profound time-dependent block after channel activation, consistent with preferential LA binding to BTX-modified open channels. We propose that channel opening promotes better exposure of receptor sites for binding with BTX and LAs, possibly by widening the bordering area around D1-S6, D4-S6, and the pore region. The BTX receptor is probably located at the interface of D1-S6 and D4-S6 segments adjacent to the LA receptor. These two S6 segments may appose too closely to bind BTX and LAs simultaneously when the channel is in its resting closed state.

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Selected References

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