Characterization of two novel forms of the rat sulphonylurea receptor SUR1A2 and SUR1BDelta31.
1. The ATP-sensitive potassium channel (K(ATP)) of pancreatic beta-cells is composed of the sulphonylurea-binding protein, SUR1, and the inwardly rectifying K(+) channel subunit, Kir6.2. We have characterized two novel isoforms of rat SUR1 in the RINm5F insulin-secreting cell line. 2. SUR1A2 is an allelic variant with a single amino acid change in the first nucleotide-binding domain. Coinjection of SUR1A2 plus Kir6.2 into Xenopus oocytes or expression of a SUR1A2-Kir6.2 tandem in HEK-293 cells yielded large currents with characteristics similar to the wild-type K(ATP) channel. 3. SUR1BDelta31, detected in several human tissues, is a splice variant of the rat SUR1 gene that lacks exon 31 of the corresponding human SUR1 gene. SUR1BDelta31 lacks the TM16-TM17 transmembrane-spanning helices leading to a protein with a different transmembrane topology. Coinjection of SUR1BDelta31 plus Kir6.2 into Xenopus oocytes or expression of the Kir6.2/SUR1BDelta31 tandem construct in HEK-293 cells did not result in any current, and a surface expression assay indicated that this channel does not reach the plasma membrane. 4. SUR1A2 and SUR1A1 proteins expressed in HEK-293 cells display similar binding affinities for [(3)H]-glibenclamide, while SUR1BDelta31 shows a 500-fold lower affinity. 5. These findings confirm that TM16-TM17 of SUR1 are important for high-affinity glibenclamide binding and that their deletion impairs trafficking of the K(ATP) channel to the surface membrane.
Institut National de la Santé et de la Recherche Médicale INSERM U376, CHU Arnaud-de-Villeneuve, 34295 Montpellier Cedex, France. gros@igm.cnrs-mop.fr
Laurent
L
Gros
Stefan
S
Trapp
Michael
M
Dabrowski
Frances M
FM
Ashcroft
Dominique
D
Bataille
Philippe
P
Blache
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D005905:Glyburide / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D009865:Oocytes; D009928:Organ Specificity; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D020033:Protein Isoforms; D011869:Radioligand Assay; D051381:Rats; D011955:Receptors, Drug / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D064233:Sulfonylurea Receptors; D014981:Xenopus
C577507:ABCC8 protein, human; D018528:ATP-Binding Cassette Transporters; C577509:Abcc8 protein, rat; D007328:Insulin; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000255:Adenosine Triphosphate; D005905:Glyburide