Functional effects of KCNJ11 mutations causing neonatal diabetes: enhanced activation by MgATP
Open Access
- 8 August 2005
- journal article
- research article
- Published by Oxford University Press (OUP) in Human Molecular Genetics
- Vol. 14 (18), 2717-2726
- https://doi.org/10.1093/hmg/ddi305
Abstract
Recent studies have shown that heterozygous mutations in KCNJ11 , which encodes Kir6.2, the pore-forming subunit of the ATP-sensitive potassium (K ATP ) 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 Mg 2+ , to isolate the inhibitory effects of ATP on Kir6.2, showed that both types of mutation reduce channel inhibition by ATP. However, in pancreatic β-cells, K ATP 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 ATP channels expressed in Xenopus oocytes. In contrast to wild-type channels, Mg 2+ 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 ATP channels in two ways: by increasing MgATP activation and by decreasing ATP inhibition. They further show that the fraction of unblocked K ATP current at physiological MgATP concentrations correlates with the severity of the clinical phenotype.Keywords
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