Molecular mechanisms underlying ketamine-mediated inhibition of sarcolemmal adenosine triphosphate-sensitive potassium channels.
BACKGROUND
Ketamine inhibits adenosine triphosphate-sensitive potassium (KATP) channels, which results in the blocking of ischemic preconditioning in the heart and inhibition of vasorelaxation induced by KATP channel openers. In the current study, the authors investigated the molecular mechanisms of ketamine's actions on sarcolemmal KATP channels that are reassociated by expressed subunits, inwardly rectifying potassium channels (Kir6.1 or Kir6.2) and sulfonylurea receptors (SUR1, SUR2A, or SUR2B).


METHODS
The authors used inside-out patch clamp configurations to investigate the effects of ketamine on the activities of reassociated Kir6.0/SUR channels containing wild-type, mutant, or chimeric SURs expressed in COS-7 cells.


RESULTS
Ketamine racemate inhibited the activities of the reassociated KATP channels in a SUR subtype-dependent manner: SUR2A/Kir6.2 (IC50 = 83 microM), SUR2B/Kir6.1 (IC50 = 77 microM), SUR2B/Kir6.2 (IC50 = 89 microM), and SUR1/Kir6.2 (IC50 = 1487 microM). S-(+)-ketamine was significantly less potent than ketamine racemate in blocking all types of reassociated KATP channels. The ketamine racemate and S-(+)-ketamine both inhibited channel currents of the truncated isoform of Kir6.2 (Kir6.2DeltaC36) with very low affinity. Application of 100 mum magnesium adenosine diphosphate significantly enhanced the inhibitory potency of ketamine racemate. The last transmembrane domain of SUR2 was essential for the full inhibitory effect of ketamine racemate.


CONCLUSIONS
These results suggest that ketamine-induced inhibition of sarcolemmal KATP channels is mediated by the SUR subunit. These inhibitory effects of ketamine exhibit specificity for cardiovascular KATP channels, at least some degree of stereoselectivity, and interaction with intracellular magnesium adenosine diphosphate.
Kawano
Takashi
T
Department of Anesthesiology, Tokushima University School of Medicine, Tokushima, Japan. haf2670@ams.odn.ne.jp
Oshita
Shuzo
S
Takahashi
Akira
A
Tsutsumi
Yasuo
Y
Tanaka
Katsuya
K
Tomiyama
Yoshinobu
Y
Kitahata
Hiroshi
H
Nakaya
Yutaka
Y
D018528:ATP-Binding Cassette Transporters; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D054086:KATP Channels; D007649:Ketamine / Q000737:chemistry / Q000494:pharmacology*; D009154:Mutation; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects* / Q000235:genetics; D024661:Potassium Channels, Inwardly Rectifying; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000187:drug effects; D012508:Sarcolemma / Q000187:drug effects / Q000201:enzymology*; D013237:Stereoisomerism; D014162:Transfection
D018528:ATP-Binding Cassette Transporters; D018076:DNA, Complementary; D018691:Excitatory Amino Acid Antagonists; D054086:KATP Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011993:Recombinant Fusion Proteins; C092520:uK-ATP-1 potassium channel; D000244:Adenosine Diphosphate; D007649:Ketamine