Functional effects of <it>KCNJ11</it> mutations causing neonatal diabetes: enhanced activation by MgATP
Authors: Proks, Peter; Girard, Christophe; Ashcroft, Frances M.
Source: Human Molecular Genetics, Volume 14, Number 18, 15 September 2005 , pp. 2717-2726(10)
Publisher: Oxford University Press
Abstract:Recent studies have shown that heterozygous mutations in KCNJ11, which encodes Kir6.2, the pore-forming subunit of the ATP-sensitive potassium (K<inf>ATP</inf>) channel, cause permanent neonatal diabetes either alone (R201C, R201H) or in association with developmental delay, muscle weakness and epilepsy (V59G,V59M). Functional analysis in the absence of Mg2+, to isolate the inhibitory effects of ATP on Kir6.2, showed that both types of mutation reduce channel inhibition by ATP. However, in pancreatic -cells, K<inf>ATP</inf> channel activity is governed by the balance between ATP inhibition via Kir6.2 and Mg-nucleotide stimulation mediated by an auxiliary subunit, the sulphonylurea receptor SUR1. We therefore studied the MgATP sensitivity of KCNJ11 mutant K<inf>ATP</inf> channels expressed in Xenopus oocytes. In contrast to wild-type channels, Mg2+ dramatically reduced the ATP sensitivity of heterozygous R201C, R201H, V59M and V59G channels. This effect was predominantly mediated via the nucleotide-binding domains of SUR1 and resulted from an enhanced stimulatory action of MgATP. Our results therefore demonstrate that KCNJ11 mutations increase the current magnitude of heterozygous K<inf>ATP</inf> channels in two ways: by increasing MgATP activation and by decreasing ATP inhibition. They further show that the fraction of unblocked K<inf>ATP</inf> current at physiological MgATP concentrations correlates with the severity of the clinical phenotype.
Document Type: Research article
Publication date: 2005-09-15
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