Gating dependence of inner pore access in inward rectifier K(+) channels.
Cation channel gating may occur either at or below the inner vestibule entrance or at the selectivity filter. To differentiate these possibilities in inward rectifier (Kir) channels, we examined cysteine accessibility in the ATP-gated Kir6.2 channel. MTSEA and MTSET both block channels and modify M2 cysteines with identical voltage dependence. If entry is restricted to open channels, modification rates will slow in ATP-closed channels, but because the reagent can be trapped in the pore following brief openings, this may not be apparent until open probability is extremely low (<0.01). When these conditions are met, modification does slow significantly, indicating gated access and highlighting an important caveat for interpretation of MTS-accessibility measurements: reagent "trapping" in nominally "closed" channels may obscure gated access.
Phillips
L Revell
LR
Department of Cell Biology and Physiology, Washington University School of Medicine, 660 South Euclid Avenue, Saint Louis, MO 63110, USA.
Enkvetchakul
Decha
D
Nichols
Colin G
CG
D000255:Adenosine Triphosphate / Q000494:pharmacology; D002460:Cell Line; D005020:Ethyl Methanesulfonate / Q000031:analogs & derivatives* / Q000494:pharmacology; D015870:Gene Expression; D007202:Indicators and Reagents; D015640:Ion Channel Gating / Q000502:physiology*; D008698:Mesylates / Q000494:pharmacology; D008839:Microelectrodes; D009154:Mutation; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D014162:Transfection
D007202:Indicators and Reagents; D008698:Mesylates; D024661:Potassium Channels, Inwardly Rectifying; C093171:methanethiosulfonate ethylammonium; C109154:(2-(trimethylammonium)ethyl)methanethiosulfonate; D000255:Adenosine Triphosphate; D005020:Ethyl Methanesulfonate; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases