Modulation of HERG affinity for E-4031 by [K+]o and C-type inactivation.
Rectification of HERG is due to a rapid inactivation process that has been labeled C-type inactivation and is believed to be due to closure of the external mouth of the pore. We examined the effects of mutation of extracellular residues that remove C-type inactivation on binding of the intracellularly acting methanesulfonanilide drug E-4031. Removal of inactivation through mutation reduced drug affinity by more than an order of magnitude. Elevation of [K+]o in the wild-type channel reduces channel affinity for E-4031. Elevation of [K+]o also interferes with the extracellular pore mouth closure associated with C-type inactivation through a 'foot in the door' mechanism. We examined the possibility that [K+]o elevation reduces drug binding through inhibition of C-type inactivation by comparing drug block in the wild-type and inactivation-removed mutant channels. Elevation of [K+]o decreased affinity in both channel constructs by a roughly equal amount. These results suggest that [K+]o alters drug binding affinity independently of its effects on C-type inactivation. They further suggest that inhibition of pore mouth closure by elevated [K+]o does not have same effect on drug affinity as mutations removing C-type inactivation.
Wang
S
S
Department of Medicine, Duke University Medical Center, Durham, NC 27708-0281, USA.
Morales
M J
MJ
Liu
S
S
Strauss
H C
HC
Rasmusson
R L
RL
D000818:Animals; D027682:Cation Transport Proteins; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D011725:Pyridines / Q000378:metabolism*; D014982:Xenopus laevis
D027682:Cation Transport Proteins; D051638:Ether-A-Go-Go Potassium Channels; C092509:KCNH6 protein, human; D010880:Piperidines; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011725:Pyridines; C063968:E 4031; D011188:Potassium