A conserved tryptophan at the membrane-water interface acts as a gatekeeper for Kir6.2/SUR1 channels and causes neonatal diabetes when mutated. by Männikkö, R, Stansfeld, P, Ashcroft, A, Hattersley, A, Sansom, MS, Ellard, S, Ashcroft, F

“…The functional effects of mutations at residue 68 of Kir6.2 were studied by heterologous expression in Xenopus oocytes, and by homology modelling. We found the Kir6.2-W68R mutation causes a small reduction in ATP inhibition in the heterozygous state and an increase in the whole-cell KATP current. …”

A gating mutation at the internal mouth of the Kir6.2 pore is associated with DEND syndrome. by Proks, P, Girard, C, Haider, S, Gloyn, A, Hattersley, A, Sansom, MS, Ashcroft, F

“…We investigated the functional effects of the I296L mutation by expressing wild-type or mutant Kir6.2/SUR1 channels in Xenopus oocytes. The mutation caused a marked increase in resting whole-cell K(ATP) currents by reducing channel inhibition by ATP, in both homomeric and simulated heterozygous states. …”

A novel mutation causing DEND syndrome: a treatable channelopathy of pancreas and brain. by Shimomura, K, Horster, F, De Wet, H, Flanagan, SE, Ellard, S, Hattersley, A, Wolf, N, Ashcroft, F, Ebinger, F

“…We carried out electrophysiologic analysis of wild-type and mutant K(ATP) channels heterologously expressed in Xenopus oocytes. RESULTS: We identified a novel Kir6.2 mutation (I167L) causing DEND syndrome. …”

Mutations at the same residue (R50) of Kir6.2 (KCNJ11) that cause neonatal diabetes produce different functional effects. by Shimomura, K, Girard, C, Proks, P, Nazim, J, Lippiat, J, Cerutti, F, Lorini, R, Ellard, S, Hattersley, A, Barbetti, F, Ashcroft, F

“…Wild-type or mutant Kir6.2/SUR1 channels were examined by heterologous expression in Xenopus oocytes. Both mutations increased resting whole-cell currents through homomeric and heterozygous K(ATP) channels by reducing channel inhibition by ATP, an effect that was larger in the presence of Mg(2+). …”

Molecular basis of Kir6.2 mutations associated with neonatal diabetes or neonatal diabetes plus neurological features. by Proks, P, Antcliff, J, Lippiat, J, Gloyn, A, Hattersley, A, Ashcroft, F

“…To determine the molecular basis of these different phenotypes, we expressed wild-type or mutant (R201C, Q52R, or V59G) Kir6.2/sulfonylurea receptor 1 channels in Xenopus oocytes. All mutations increased resting whole-cell K(ATP) currents by reducing channel inhibition by ATP, but, in the simulated heterozygous state, mutations causing PNDM alone (R201C) produced smaller K(ATP) currents and less change in ATP sensitivity than mutations associated with severe disease (Q52R and V59G). …”

Relapsing diabetes can result from moderately activating mutations in KCNJ11. by Gloyn, A, Reimann, F, Girard, C, Edghill, E, Proks, P, Pearson, E, Temple, I, Mackay, D, Shield, J, Freedenberg, D, Noyes, K, Ellard, S, Ashcroft, F, Gribble, F, Hattersley, A

“…Functional characterization of the TNDM associated mutations was performed by expressing the mutated Kir6.2 with SUR1 in Xenopus laevis oocytes. All three heterozygous mutations resulted in a reduction in the sensitivity to ATP when compared with wild-type (IC(50) approximately 30 versus approximately 7 microM, P-value for is all <0.01); however, this was less profoundly reduced than with the PNDM associated mutations. …”

Permanent neonatal diabetes: combining sulphonylureas with insulin may be an effective treatment by Misra, S, Vedovato, N, Cliff, E, De Franco, E, Hattersley, A, Ashcroft, F, Oliver, N

“…We assessed the in vitro response of the mutant channel to tolbutamide in Xenopus oocytes and undertook sulfonylurea dose‐titration with C‐peptide assessment and continuous glucose monitoring. …”

Activating mutations in the gene encoding the ATP-sensitive potassium-channel subunit Kir6.2 and permanent neonatal diabetes. by Gloyn, A, Pearson, E, Antcliff, J, Proks, P, Bruining, G, Slingerland, A, Howard, N, Srinivasan, S, Silva, J, Molnes, J, Edghill, E, Frayling, T, Temple, I, Mackay, D, Shield, J, Sumnik, Z, van Rhijn, A, Wales, J, Clark, P, Gorman, S, Aisenberg, J, Ellard, S, Njølstad, P, Ashcroft, F, Hattersley, A

“…When the most common mutation in Kir6.2 was coexpressed with sulfonylurea receptor 1 in Xenopus laevis oocytes, the ability of ATP to block mutant K(ATP) channels was greatly reduced. …”

A Kir6.2 mutation causing severe functional effects in vitro produces neonatal diabetes without the expected neurological complications. by Tammaro, P, Flanagan, SE, Zadek, B, Srinivasan, S, Woodhead, H, Hameed, S, Klimes, I, Hattersley, A, Ellard, S, Ashcroft, F

“…Functional properties of wild-type and mutant channels were examined by electrophysiology in Xenopus oocytes. RESULTS: Heterozygous (het) and homozygous L164P K(ATP) channels showed a marked reduction in channel inhibition by ATP. …”

Neonatal diabetes caused by homozygous KCNJ11 mutation demonstrates that tiny changes in ATP sensititvity markedly affect diabetes risk by Vedovato, N, Cliff, E, Proks, P, Poovazhagi, V, Flanagan, S, Ellard, S, Hattersley, A, Ashcroft, F

“…Functional properties of wild-type, heterozygous and homozygous mutant KATP channels were examined after heterologous expression in <em>Xenopus</em> oocytes.</p> <p><em>Results</em> Functional studies indicated that the Kir6.2-G324R mutation reduces the channel ATP sensitivity but that the difference in ATP inhibition between homozygous and heterozygous channels is remarkably small. …”

Switching from insulin to oral sulfonylureas in patients with diabetes due to Kir6.2 mutations. by Pearson, E, Flechtner, I, Njølstad, P, Malecki, M, Flanagan, SE, Larkin, B, Ashcroft, F, Klimes, I, Codner, E, Iotova, V, Slingerland, A, Shield, J, Robert, J, Holst, J, Clark, P, Ellard, S, Søvik, O, Polak, M, Hattersley, A

“…The response of mutant K(ATP) channels to the sulfonylurea tolbutamide was assayed in xenopus oocytes. RESULTS: A total of 44 patients (90 percent) successfully discontinued insulin after receiving sulfonylureas. …”

Mutations of the same conserved glutamate residue in NBD2 of the sulfonylurea receptor 1 subunit of the KATP channel can result in either hyperinsulinism or neonatal diabetes. by Männikkö, R, Flanagan, SE, Sim, X, Segal, D, Hussain, K, Ellard, S, Hattersley, A, Ashcroft, F

“…Wild-type and mutant K_ATP channels were expressed in <em>Xenopus laevis</em> oocytes and studied with electrophysiological methods.…”