Mechanism of cardiac sarcolemmal adenosine triphosphate-sensitive potassium channel activation by isoflurane in a heterologous expression system.
BACKGROUND
Activation of the cardiac sarcolemmal adenosine triphosphate-sensitive potassium (KATP) channel during metabolic stress initiates cellular events that preserve cardiac performance. Previous studies showed that halogenated anesthetics prime KATP channels under whole cell voltage clamp and act in intracellular pH (pHi)-dependent manner on KATP channels in excised membrane patches. However, it is not known how halogenated anesthetics interact with these channels.


METHODS
The authors evaluated the effect of pHi and isoflurane on the KATP channel subunits, the pore-forming inward rectifier Kir6.2, and the regulatory sulfonylurea receptor SUR2A, using HEK293 cells as a heterologous expression system. Single channel activity was recorded in the inside-out patch configuration.


RESULTS
At pHi 7.4, isoflurane had negligible effect on activity of wild-type Kir6.2/SUR2A, but at pHi 6.8, the channel open probability was increased by isoflurane (0.177 +/- 0.077 to 0.364 +/- 0.164). By contrast, the open probability of truncated Kir6.2DeltaC26, which forms a functional channel without SUR2A, was attenuated by isoflurane at both pHi 7.4 and pHi 6.8. Coexpression of Kir6.2DeltaC26 with SUR2A restored pHi sensitivity of channel activation by isoflurane. Site-directed mutagenesis within the Walker motifs of SUR2A abolished isoflurane activation of KATP channel at pHi 6.8. In addition, the pancreatic-type channels expressing sulfonylurea receptor SUR1 could not be activated by isoflurane.


CONCLUSIONS
The nucleotide binding domains of SUR2A play a crucial role in isoflurane facilitation of the KATP channel activity at moderately acidic pHi as would occur during early ischemia. These findings support direct and differential interaction of isoflurane with the subunits of the cardiac sarcolemmal KATP channel.
Bienengraeber
Martin
M
Department of Anesthesiology, Medical College of Wisconsin, Wisconsin 53226, USA.
Warltier
David C
DC
Bosnjak
Zeljko J
ZJ
Stadnicka
Anna
A
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D018685:Anesthetics, Inhalation; D001665:Binding Sites; D002478:Cells, Cultured; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007530:Isoflurane / Q000494:pharmacology*; D015221:Potassium Channels / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D011955:Receptors, Drug / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D013329:Structure-Activity Relationship; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D018685:Anesthetics, Inhalation; D007530:Isoflurane; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel; C577507:ABCC8 protein, human; C577510:ABCC9 protein, human