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J Korean Diabetes Assoc. 2003 Aug;27(4):332-342. Korean. Original Article.
Kwon OD , Lim JG , Kim HG , Kim DK , Hwang JS , Park KG , Park SH , Cho CH , Lee IK , Song DK .
Department of Neurology, Daegu Catholic Medical Center, Korea.
Department of Neurology, Keimyung University School of Medicine, Daegu, Korea.
Department of Physiology & CDR center, Keimyung University School of Medicine, Daegu, Korea.
Department of Internal Medicine, Keimyung University School of Medicine, Daegu, Korea.
Department of Anesthesiology, College of Medicine, Dongkuk University, Kyungju, Korea.
Abstract

BACKGROUND: The ATP-sensitive potassium (KATP) channel comprises an inwardly- rectifying K+ channel (Kir) and a sulfonylurea receptor(SUR). This study investigated the mechanism of different ATP sensitivity between skeletal-(Kir6.2/SUR2A) and smooth muscle- (Kir6.2/SUR2B) type KATP channels. METHODS: Messenger RNAs encoding mouse Kir6.2, and rat SUR2A or 2B were co-injected into Xenopus Laevis oocytes to express each type of KATP channel. Using the inside-out patch clamp technique, the channel currents for MgATP sensitivity were measured and analyzed. RESULTS: By addition of 100 microM of MgATP, the current initially decreased and then slowly increased in Kir6.2/SUR2A. This gradual, ATP sensitivity decrease during prolonged MgATP application was totally blocked by LY 294002, a pho- sphatidylinositol-3 and -4 kinase inhibitor. In contrast, a rather rapid sensitivity decrease after initial inhibition was observed in Kir6.2/SUR2B by 100 microM of ATP, which was not blocked by LY 294002. This channel activation was Mg2+- dependent, suggesting that ATP hydrolysis is critical. CONCLUSION: This result supports the idea that the ability of MgATP to stimulate Kir6.2/SUR2B channels reflects a faster rate of ATP hydrolysis at NBD2 of SUR2B.

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