Incomplete dissociation of glibenclamide from wild-type and mutant pancreatic K ATP channels limits their recovery from inhibition.
OBJECTIVE
The antidiabetic sulphonylurea, glibenclamide, acts by inhibiting the pancreatic ATP-sensitive K(+) (K(ATP)) channel, a tetradimeric complex of K(IR)6.2 and sulphonylurea receptor 1 (K(IR)6.2/SUR1)(4). At room temperature, recovery of channel activity following washout of glibenclamide is very slow and cannot be measured. This study investigates the relation between the recovery of channel activity from glibenclamide inhibition and the dissociation rate of [(3)H]-glibenclamide from the channel at 37 degrees C.


METHODS
K(IR)6.2, K(IR)6.2DeltaN5 or K(IR)6.2DeltaN10 (the latter lacking amino-terminal residues 2-5 or 2-10 respectively) were coexpressed with SUR1 in HEK cells. Dissociation of [(3)H]-glibenclamide from the channel and recovery of channel activity from glibenclamide inhibition were determined at 37 degrees C.


RESULTS
The dissociation kinetics of [(3)H]-glibenclamide from the wild-type channel followed an exponential decay with a dissociation half-time, t(1/2)(D) = 14 min; however, only limited and slow recovery of channel activity was observed. t(1/2)(D) for K(IR)6.2DeltaN5/SUR1 channels was 5.3 min and recovery of channel activity exhibited a sluggish sigmoidal time course with a half-time, t(1/2)(R) = 12 min. t(1/2)(D) for the DeltaN10 channel was 2.3 min; recovery kinetics were again sigmoidal with t(1/2)(R) approximately 4 min.


CONCLUSIONS
The dissociation of glibenclamide from the truncated channels is the rate-limiting step of channel recovery. The sigmoidal recovery kinetics are in quantitative agreement with a model where glibenclamide must dissociate from all four (or at least three) sites before the channel reopens. It is argued that these conclusions hold also for the wild-type (pancreatic) K(ATP) channel.
Russ
U
U
Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstrasse 56, Tübingen, Germany.
Kühner
P
P
Prager
R
R
Stephan
D
D
Bryan
J
J
Quast
U
U
D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D005905:Glyburide / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007004:Hypoglycemic Agents / Q000378:metabolism* / Q000494:pharmacology; D015640:Ion Channel Gating; D054086:KATP Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D010179:Pancreas / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011955:Receptors, Drug / Q000235:genetics / Q000378:metabolism; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D005905:Glyburide; D007004:Hypoglycemic Agents; D054086:KATP Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel; C577507:ABCC8 protein, human; C577508:Abcc8 protein, mouse; C577509:Abcc8 protein, rat