Isoflurane activates sarcolemmal adenosine triphosphate-sensitive potassium channels in vascular smooth muscle cells: a role for protein kinase A.
BACKGROUND
Recent evidence indicates that vascular adenosine triphosphate-sensitive potassium (K(ATP)) channels in vascular smooth muscle cells are critical in the regulation of vascular tonus under both physiologic and pathophysiologic conditions. Studies of the interaction of volatile anesthetics with vascular K(ATP) channels have been limited. In the current study, the authors investigated the molecular mechanism of isoflurane's action on vascular K(ATP) channels.


METHODS
Electrophysiologic experiments were performed using cell-attached and inside-out patch clamp techniques to monitor native vascular K(ATP) channels, and recombinant K(ATP) channels comprised of inwardly rectifying potassium channel subunits (Kir6.1) and the sulfonylurea receptor (SUR2B). Isometric tension experiments were performed in rat thoracic aortic rings without endothelium.


RESULTS
Application of isoflurane (0.5 mM) to the bath solution during cell-attached recordings induced a significant increase in K(ATP) channel activity, which was greatly reduced by pretreatment with a selective inhibitor of protein kinase A (PKA), Rp-cAMPS (100 microM). In inside-out patches, isoflurane did not activate K(ATP) channels. Isoflurane significantly activated wild-type recombinant SUR2B/Kir6.1 in cell-attached patches. Isoflurane-induced activation of wild-type channels was diminished in the PKA-insensitive mutant SUR2B-T633A/Kir6.1, SUR2B-S1465A/Kir6.1, and SUR2B/Kir6.1-S385A. In addition, the authors demonstrated that isoflurane-induced PKA activation was associated with isoflurane-induced decreases in isometric tension in the rat aorta.


CONCLUSIONS
These results indicate that isoflurane activates K(ATP) channels via PKA activation. PKA-dependent vasodilation induced by isoflurane also was observed in isometric tension experiments. Analysis of expressed vascular-type K(ATP) channels suggested that PKA-mediated phosphorylation of both Kir6.1 and SUR2B subunits plays a pivotal role in isoflurane-induced vascular K(ATP) channel activation.
Tanaka
Katsuya
K
Department of Anesthesiology, Tokushima University School of Medicine, Kuramoto, Tokushima, Japan. katsuya@clin.med.tokushima-u.ac.jp
Kawano
Takashi
T
Nakamura
Akiyo
A
Nazari
Hossein
H
Kawahito
Shinji
S
Oshita
Shuzo
S
Takahashi
Akira
A
Nakaya
Yutaka
Y
D018528:ATP-Binding Cassette Transporters / Q000187:drug effects*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D007530:Isoflurane / Q000494:pharmacology*; D054086:KATP Channels; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects*; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D011955:Receptors, Drug / Q000187:drug effects*; D012508:Sarcolemma / Q000378:metabolism*; D064233:Sulfonylurea Receptors; D014664:Vasodilation / Q000187:drug effects
D018528:ATP-Binding Cassette Transporters; D018685:Anesthetics, Inhalation; D054086:KATP Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; C092520:uK-ATP-1 potassium channel; D000255:Adenosine Triphosphate; D007530:Isoflurane; D017868:Cyclic AMP-Dependent Protein Kinases