Two SUR1-specific histidine residues mandatory for zinc-induced activation of the rat KATP channel.
Zinc at micromolar concentrations hyperpolarizes rat pancreatic beta-cells and brain nerve terminals by activating ATP-sensitive potassium channels (KATP). The molecular determinants of this effect were analyzed using insulinoma cell lines and cells transfected with either wild type or mutated KATP subunits. Zinc activated KATP in cells co-expressing rat Kir6.2 and SUR1 subunits, as in insulinoma cell lines. In contrast, zinc exerted an inhibitory action on SUR2A-containing cells. Therefore, SUR1 expression is required for the activating action of zinc, which also depended on extracellular pH and was blocked by diethyl pyrocarbonate, suggesting histidine involvement. The five SUR1-specific extracellular histidine residues were submitted to site-directed mutagenesis. Of them, two histidines (His-326 and His-332) were found to be critical for the activation of KATP by zinc, as confirmed by the double mutation H326A/H332A. In conclusion, zinc activates KATP by binding itself to extracellular His-326 and His-332 of the SUR1 subunit. Thereby zinc could exert a negative control on cell excitability and secretion process of pancreatic beta-and alpha-cells. In fact, we have recently shown that such a mechanism occurs in hippocampal mossy fibers, a brain region characterized, like the pancreas, by an important accumulation of zinc and a high density of SUR1-containing KATP.
Bancila
Victor
V
Neurosciences Fondamentales, CMU, 1 rue Michel Servet, 1211 Genève 04, Switzerland.
Cens
Thierry
T
Monnier
Dominique
D
Chanson
Frédéric
F
Faure
Cécile
C
Dunant
Yves
Y
Bloc
Alain
A
D018528:ATP-Binding Cassette Transporters; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D006639:Histidine; D006801:Humans; D007340:Insulinoma; D007668:Kidney; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D016297:Mutagenesis, Site-Directed; D010190:Pancreatic Neoplasms; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011955:Receptors, Drug; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D064233:Sulfonylurea Receptors; D015032:Zinc / Q000494:pharmacology*; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D006639:Histidine; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D011994:Recombinant Proteins; D064233:Sulfonylurea Receptors; D015032:Zinc; D000099161:Kcnj11 Channel; C577507:ABCC8 protein, human; C577510:ABCC9 protein, human; C577509:Abcc8 protein, rat