Functional modification of a Ca2+-activated K+ channel by trimethyloxonium.
Single Ca2+-activated K+ channels from rat skeletal muscle plasma membranes were studied in neutral phospholipid bilayers. Channels were chemically modified by briefly exposing the external side to the carboxyl group modifying reagent trimethyloxonium (TMO). TMO modification, in a "multi-hit" fashion, reduces the single-channel conductance without affecting ion selectivity. Modification also shifts the voltage activation curve toward more depolarized voltages and reduces the affinity of the channel blocker charybdotoxin (CTX). CTX, bound to the channel during the TMO exposure, prevents the TMO-induced reduction of the single-channel conductance. These data suggest that the high-conductance Ca2+-activated K+ channel has carboxyl groups on its external surface. These groups influence ion conduction, gating, and the binding of CTX.
MacKinnon
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R
Howard Hughes Medical Institute, Brandeis University, Waltham, Massachusetts 02254.
Miller
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C
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D018999:Charybdotoxin; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D015640:Ion Channel Gating / Q000187:drug effects; D008051:Lipid Bilayers; D009861:Onium Compounds / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D012604:Scorpion Venoms / Q000494:pharmacology
D007202:Indicators and Reagents; D008051:Lipid Bilayers; D009861:Onium Compounds; D015221:Potassium Channels; D012604:Scorpion Venoms; D018999:Charybdotoxin; D011189:Potassium Chloride; C009576:trimethyloxonium; D002118:Calcium