ATP-sensitive K⁺-channel Subunits on the Mitochondria and Endoplasmic Reticulum of Rat Cardiomyocytes

Ming Zhou ^1*, Osamu Tanaka ¹, Masaki Sekiguchi ¹, Hui-jing He ¹, Yukiko Yasuoka ¹, Hideaki Itoh ¹, Katsumasa Kawahara ¹ and Hiroshi Abe ¹

¹ Department of Anatomy, Akita University School of Medicine, Akita, Japan (MZ,H-jH,HA); Department of Material-process Engineering and Applied Chemistry for Environment, Akita University Faculty of Engineering and Resource Science, Akita, Japan (HI); Department of Morphology, Tokai University School of Medicine, Bohseidai, Isehara, Kanagawa, Japan (OT,MS); and Department of Physiology, Kitasato University School of Medicine, Sagamihara, Kanagawa, Japan (YY,KK)

^* To whom correspondence should be addressed. E-mail: mzhou{at}med.akita-u.ac.jp.

Submitted on May 18, 2005
Accepted on 1 June 2005

	Abstract

ATP-sensitive K⁺ (K_ATP) channel subunits on the subcellular structures of rat cardiomyocytes were studied with antibodies against Kir6.1 and Kir6.2. According to the results of Western blot analysis, Kir6.1 was strongly expressed in mitochondrial and microsome fractions, and faintly expressed in cell membrane fraction, whereas Kir6.2 was mainly expressed in the microsome fraction and weakly in cell membrane and mitochondrial fractions. Immunohistochemistry showed that Kir6.1 and Kir6.2 were expressed in the endocardium, atrial and ventricular myocardium, and in vascular smooth muscles. Immunoelectron microscopy revealed that Kir6.1 immunoreactivity was mainly localized in the mitochondria, whereas Kir6.2 immunoreactivity was mainly localized in the endoplasmic reticulum and a few in the mitochondria. Both Kir6.1 and Kir6.2 are candidates of mitochondrial K_ATP channel subunits. The data obtained in this study will be useful for analyzing the composition of K_ATP channels of cardiomyocytes, and help to understanding the cardioprotective role of K_ATP channels during heart ischemia.

Key Words: ATP-sensitive K⁺ channels, mitochondria, endoplasmic reticulum, rat, cardiomyocytes, immunoelectron microscopy

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