Key result
The N999S mutation produced a strong gain-of-function effect on BK currents, shifting them to negative potentials with faster activation and slower deactivation compared to wild type and D434G.
Why the study?
The effects of BK channel mutations N999S and N999S/R1128W had not been reported under physiological K+ conditions or compared to D434G.
The N999S mutation is a strong gain-of-function mutation in BK channels that surpasses the D434G phenotype, and these channels are not directly modulated by acetazolamide.
Answers are grounded in this paper and cite their sources.
Expands KCNMA1 variants linked to epilepsy; leaves open functional effects of N999S/R1128W on BK channels.
KCNMA1, encoding the voltage- and calcium-activated potassium channel, has a pivotal role in brain physiology. Mutations in KCNMA1 are associated with epilepsy and/or dyskinesia (PNKD3). Two KCNMA1 mutations correlated with these phenotypes, D434G and N999S, were previously identified as producing gain-of-function (GOF) effects on BK channel activity. Three new patients have been reported harboring N999S, one carrying a second mutation, R1128W, but the effects of these mutations have not yet been reported under physiological K+ conditions or compared to D434G. In this study, we characterize N999S, the novel N999S/R1128W double mutation, and D434G in a brain BK channel splice variant, comparing the effects on BK current properties under a physiological K+ gradient with action potential voltage commands. N999S, N999S/R1128W, and D434G cDNAs were expressed in HEK293T cells and characterized by patch-clamp electrophysiology. N999S BK currents were shifted to negative potentials, with faster activation and slower deactivation compared with wild type (WT) and D434G. The double mutation N999S/R1128W did not show any additional changes in current properties compared with N999S alone. The antiepileptic drug acetazolamide was assessed for its ability to directly modulate WT and N999S channels. Neither the WT nor N999S channels were sensitive to the antiepileptic drug acetazolamide, but both were sensitive to the inhibitor paxilline. We conclude that N999S is a strong GOF mutation that surpasses the D434G phenotype, without mitigation by R1128W. Acetazolamide has no direct modulatory action on either WT or N999S channels, indicating that its use may not be contraindicated in patients harboring GOF KCNMA1 mutations. NEW & NOTEWORTHY KCNMA1-linked channelopathy is a new neurological disorder characterized by mutations in the BK voltage- and calcium-activated potassium channel. The epilepsy- and dyskinesia-associated gain-of-function mutations N999S and D434G comprise the largest number of patients in the cohort. This study provides the first direct comparison between D434G and N999S BK channel properties as well as a novel double mutation, N999S/R1128W, from another patient, defining the functional effects during an action potential stimulus.
No takes yet. Share an insight, caveat, or question.
Moldenhauer et al. (2019) studied KCNMA1-linked channelopathy (epilepsy and/or dyskinesia). KCNMA1 mutations (N999S, N999S/R1128W) vs. Wild type (WT) and D434G was evaluated on BK current properties (activation, deactivation, voltage shift). The N999S mutation produced a strong gain-of-function effect on BK currents, shifting them to negative potentials with faster activation and slower deactivation compared to wild type and D434G.
Synapse has enriched 10 related papers. Consider them for comparative context: