Segmental exchanges define 4-aminopyridine binding and the inner mouth of K+ pores.
4-Aminopyridine (4AP) blocks the intracellular mouth of voltage-gated K+ channels. We identified critical regions for 4AP binding with chimeric channels in which segments of a low affinity clone (Kv2.1, IC50 = 18 mM) were replaced with those of a high affinity clone (Kv3.1, IC50 = 0.1 mM). 4AP sensitivity was not transferred with the S5-S6 linker (pore or P region). Instead, a chimera of the cytoplasmic half of S6 increased block 20-fold, without affecting gating. A double chimera of the cytoplasmic halves of S5 and S6 fully transferred 4AP sensitivity. Because 4AP block was inhibited by tetrapentylammonium, we conclude that determinants of 4AP binding lie in the S6 segment that forms the cytoplasmic vestibule of the pore and that this site may overlap a quaternary ammonium site.
Department of Anesthesiology, Baylor College of Medicine, Houston, Texas 77030.
G E
GE
Kirsch
C C
CC
Shieh
J A
JA
Drewe
D F
DF
Vener
A M
AM
Brown
D015761:4-Aminopyridine / Q000378:metabolism* / Q000494:pharmacology; D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002678:Chimera; D007425:Intracellular Membranes / Q000378:metabolism*; D015640:Ion Channel Gating; D008969:Molecular Sequence Data; D009154:Mutation; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism
D015221:Potassium Channels; D000644:Quaternary Ammonium Compounds; C027435:tetrapentylammonium; D015761:4-Aminopyridine