Functional interaction between extracellular sodium, potassium and inactivation gating in HERG channels.
We have studied the interaction between extracellular K(+) (K(+)(o)) and extracellular Na(+) (Na(+)(o)) in human ether-à-go-go related gene (HERG)-encoded K(+) channels expressed in Chinese hamster ovary (CHO-K1) cells, using the whole-cell voltage clamp technique. Prior studies indicate that Na(+)(o) potently inhibits HERG current (IC(50) 3 mm) by binding to an outer pore site, and also speeds recovery from inactivation. In this study, we sought to explore the relationship between the Na(+)(o) effect on recovery and Na(+)(o) inhibition of HERG current, and to determine whether inactivation gating plays a critical role in Na(+)(o) inhibition of HERG current. Na(+)(o) concentration-response relationships for current inhibition and speeding of recovery were different, with Na(+)(o) less potent at speeding recovery. Na(+)(o) inhibition of HERG current was relieved by physiological [K(+)](o), while Na(+)(o) speeded recovery from inactivation similarly in the absence or presence of physiological [K(+)](o). To examine the link between Na(+)(o) block and inactivation using an independent approach, we studied hyperpolarization-activated currents uncoupled from inactivation in the S4-S5 linker mutant D540K. Depolarization-activated D540K currents were inhibited by Na(+)(o), while hyperpolarization-activated currents were augmented by Na(+)(o). This result reveals a direct link between Na(+)(o) inhibition and a depolarization-induced conformational change, most likely inactivation. We attempted to simulate the disparate concentration-response relationships for the two effects of Na(+)(o) using a kinetic model that included Na(+)(o) site(s) affected by permeation and gating. While a model with only a single dynamic Na(+)(o) site was inadequate, a model with two distinct Na(+)(o) sites was sufficient to reproduce the data.
Mullins
Franklin M
FM
Room 560 PRB (MRB II), Vanderbilt University School of Medicine, Nashville, TN 37232, USA. jeff.balser@mcmail.vanderbilt.edu
Stepanovic
Svetlana Z
SZ
Gillani
Niloufar B
NB
George
Alfred L
AL
Balser
Jeffrey R
JR
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D045604:Extracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D024642:Potassium Channels, Voltage-Gated; D012964:Sodium; D011188:Potassium