Cloning and functional characterization of a novel ATP-sensitive potassium channel ubiquitously expressed in rat tissues, including pancreatic islets, pituitary, skeletal muscle, and heart.
ATP-sensitive K+ (KATP) channels play a crucial role in coupling metabolic energy to the membrane potential of cells. We have isolated a cDNA encoding a novel member (uKATP-1) of the inward rectifier K+ channel family from a rat pancreatic islet cDNA library. Rat uKATP-1 is a 424-amino acid residue protein (M(r) = 47,960). Electrophysiological studies of uKATP-1 expressed in Xenopus laevis oocytes show that uKATP-1 is a weak rectifier and is blocked with Ba2+ ions. Single-channel patch clamp study of clonal human kidney epithelial cells (HEK293) transfected with uKATP-1 cDNA reveals that uKATP-1 closes in response to 1 mM ATP and has a single channel conductance of 70 +/- 2 picosiemens (n = 6), indicating that uKATP-1 is an ATP-sensitive inward rectifier K+ channel. In addition, uKATP-1 is activated by the KATP channel opener, diazoxide. RNA blot analysis shows that uKATP-1 mRNA is expressed ubiquitously in rat tissues, including pancreatic islets, pituitary, skeletal muscle, and heart, suggesting that uKATP-1 may play a physiological role as a link between the metabolic state and membrane K+ permeability of cells in almost every normal tissue. Since uKATP-1 shares only 43-46% amino acid identity with members of previously reported inward rectifier K+ channel subfamilies, including ROMK1, IRK1, GIRK1, and cKATP-1, uKATP-1 is not an isoform of these subfamilies and, therefore, represents a new subfamily of the inward rectifier K+ channel family having two transmembrane segments.
Inagaki
N
N
Division of Molecular Medicine, Chiba University School of Medicine, Japan.
Tsuura
Y
Y
Namba
N
N
Masuda
K
K
Gonoi
T
T
Horie
M
M
Seino
Y
Y
Mizuta
M
M
Seino
S
S
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D005260:Female; D015870:Gene Expression; D015723:Gene Library; D007515:Islets of Langerhans / Q000378:metabolism*; D054086:KATP Channels; D008297:Male; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism; D009865:Oocytes / Q000502:physiology; D009928:Organ Specificity; D010053:Ovary / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010902:Pituitary Gland / Q000378:metabolism*; D015221:Potassium Channels / Q000096:biosynthesis* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013737:Testis / Q000378:metabolism; D014982:Xenopus laevis
D018528:ATP-Binding Cassette Transporters; D054086:KATP Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D011994:Recombinant Proteins; C092520:uK-ATP-1 potassium channel; D000255:Adenosine Triphosphate