Endoplasmic reticulum retention of KCNQ2 potassium channel mutants following temperature elevation.

BACKGROUND: KCNQ2 plays a key role in the regulation of neuronal excitability. The R214W and Y284C mutants of KCNQ2 channels, which are associated with BFNC, can decrease channel function to cause neuronal hyperexcitability and promote seizures. Previous studies revealed that elevated temperature caused up-regulation of KCNQ2 expression. OBJECTIVE: The present study sought to investigate the impact of temperature elevation on neuronal KCNQ2 ion channel mutants. METHODS: Protein expression of wt KCNQ2 and the R214W, Y284C and truncated selective filter mutants at different temperatures was detected by live-cell confocal fluorescence microscopy and by Western blotting. Whole-cell patch clamp was performed to record the effect of temperature on the electrophysiological activity of KCNQ2 channels. RESULTS: Temperature elevation caused an unexpected increase in voltage-dependent KCNQ2 channel activation but also increased the endoplasmic reticulum (ER) retention of KCNQ2 protein, and the ER retention was greater for mutants associated with BFNC than for wt KCNQ2. Temperature elevation did not increase the fluorescence intensity of cells transfected with a truncated selective filter mutant. CONCLUSIONS: The direct effect of heat on KCNQ2 channels may be involved in excitability regulation of neurons, and the P-loop region is critical for temperature-dependent modulation of the expression and trafficking of KCNQ2 channels.

Mutación en el gen KCNH2 y el síndrome de QT largo: a propósito de un caso / Mutação no gene KCNH2 e síndrome de QT longo: um estudo de caso / KCNH2 gene mutation and long QT syndrome: a case report

Presentamos el caso de un paciente portador de una mutación en el gen KCNH2 para el síndrome de QT largo, diagnosticado a raíz de muerte súbita de un familiar. El estudio genético para el síndrome del QT largo y otras canalopatías está siendo cada vez más utilizado en la prevención de la muerte súbita, empezando a aparecer en los últimos años las primeras recomendaciones para el manejo de los pacientes portadores de mutaciones sin expresión fenotípica (AU)

We report a carrier of the KCNH2 gene for the long QT syndrome. He was diagnosed after the sudden death of a relative. The long QT syndrome (and other canalopathies) genetic study is being a new weapon for the prevention of sudden death. In last years, clinical guidelines for the management of genetic carriers without phenotypic manifestations are being published (AU)

Apresentamos um caso de um paciente portador de uma maturação no gene KHNC2 para a síndrome de QT largo, diagnosticado à raiz de morte súbita de um familiar. O estudo genético para a síndrome do QT largo e outras canalopatias estão sendo cada vez mais utilizados na prevenção da morte súbita, começando a aparecer, nos últimos anos, as primeiras recomendações para o tratamento dos pacientes portadores de mutações sem expressão fenotípica (AU)

[Site-directed mutagenesis and protein expression of KCNQ2 gene associated with neonatal convulsions].

OBJECTIVE: To study the protocol of construction of a KCNQ2-c.812G>T mutant and it's eukaryotic expression vector, the c.812G>T (p.G271V) mutation which was detected in a Chinese pedigree of benign familial infantile convulsions, and to examine the expression of mutant protein in human embyonic kidney (HEK) 293 cells. METHODS: A KCNQ2 mutation c.812G>T was engineered on KCNQ2 cDNAs cloned into pcDNA3.0 by sequence overlap extension PCR and restriction enzymes. HEK293 cells were co-transfected with pRK5-GFP and KCNQ2 plasmid (the wild type or mutant) using lipofectamine and then subjected to confocal microscopy. The transfected cells were immunostained to visualize the intracellular expression of the mutant molecules. RESULTS: Direct sequence analysis revealed a G to T transition at position 812. The c.812G>T mutation was correctly combined to eukaryotic expressive vector pcDNA3.0 and expressed in HEK293 cells. Immunostaining of transfected cells showed the expression of both the wild type and mutant molecules on the plasma membrane, which suggested that the c.812G>T mutation at the pore forming region of KCNQ2 channel did not impair normal protein expression in HEK293 cells. CONCLUSIONS: Successful construction of mutant KCNQ2 eukaryotic expression vector and expression of KCNQ2 protein in HEK293 cells provide a basis for further study on the functional effects of convulsion-causing KCNQ2 mutations and for understanding the molecular pathogenesis of epilepsy.

Distribution of M-channel subunits KCNQ2 and KCNQ3 in rat hippocampus.

Neuronal M-channels are low threshold, slowly activating and non-inactivating, voltage dependent K(+) channels that play a crucial role in controlling neuronal excitability. The native M-channel is composed of heteromeric or homomeric assemblies of subunits belonging to the Kv7/KCNQ family, with KCNQ2/3 heteromers being the most abundant form. KCNQ2 and KCNQ3 subunits have been found to be expressed in various neurons in the central and peripheral nervous system of rodents and humans. Previous evidence shows preferential localization of both subunits to axon initial segments, somata and nodes of Ranvier. In this work, we show the distribution and co-localization of KCNQ2 and KCNQ3 subunits throughout the hippocampal formation, via immunostaining experiments on unfixed rat brain slices and confocal microscopy. We find intense localization and colocalization to the axonal initial segment in several regions of the hippocampus, as well as staining for non-neuronal cells in the area of the lateral ventricle. We did not observe colocalization of KCNQ2 or KCNQ3 with the presynaptic protein, synaptophysin.

Neutralization of a negative charge in the S1-S2 region of the KV7.2 (KCNQ2) channel affects voltage-dependent activation in neonatal epilepsy.

The voltage-gated potassium channels KV7.2 and KV7.3 (genes KCNQ2 and KCNQ3) constitute a major component of the M-current controlling the firing rate in many neurons. Mutations within these two channel subunits cause benign familial neonatal convulsions (BFNC). Here we identified a novel BFNC-causing mutation (E119G) in the S1-S2 region of KV7.2. Electrophysiological investigations in Xenopus oocytes using two-microelectrode voltage clamping revealed that the steady-state activation curves for E119G alone and its coexpressions with KV7.2 and/or KV7.3 wild-type (WT) channels were significantly shifted in the depolarizing direction compared to KV7.2 or KV7.2/KV7.3. These shifts reduced the relative current amplitudes for mutant channels particularly in the subthreshold range of an action potential (about 45% reduction at --50 mV for E119G compared to KV7.2, and 33% for E119G/KV7.3 compared to KV7.2/KV7.3 channels). Activation kinetics were significantly slowed for mutant channels. Our results indicate that small changes in channel gating at subthreshold voltages are sufficient to cause neonatal seizures and demonstrate the importance of the M-current for this voltage range. This was confirmed by a computer model predicting an increased burst duration for the mutation. On a molecular level, these results reveal a critical role in voltage sensing of the negatively charged E119 in S1-S2 of KV7.2, a region that-- according to molecular modelling - might interact with a positive charge in the S4 segment.

KCNQ/M-currents contribute to the resting membrane potential in rat visceral sensory neurons.

The M-current is a slowly activating, non-inactivating potassium current that has been shown to be present in numerous cell types. In this study, KCNQ2, Q3 and Q5, the molecular correlates of M-current in neurons, were identified in the visceral sensory neurons of the nodose ganglia from rats through immunocytochemical studies. All neurons showed expression of each of the three proteins. In voltage clamp studies, the cognition-enhancing drug linopirdine (1-50 microM) and its analogue, XE991 (10 microM), quickly and irreversibly blocked a small, slowly activating current that had kinetic properties similar to KCNQ/M-currents. This current activated between -60 and -55 mV, had a voltage-dependent activation time constant of 208 +/- 12 ms at -20 mV, a deactivation time constant of 165 +/- 24 ms at -50 mV and V1/2 of -24 +/- 2 mV, values which are consistent with previous reports for endogenous M-currents. In current clamp studies, these drugs also led to a depolarization of the resting membrane potential at values as negative as -60 mV. Flupirtine (10-20 microM), an M-current activator, caused a 3-14 mV leftward shift in the current-voltage relationship and also led to a hyperpolarization of resting membrane potential. These data indicate that the M-current is present in nodose neurons, is activated at resting membrane potential and that it is physiologically important in regulating excitability by maintaining cells at negative voltages.