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Characterization of ether-a-go-go channels present in photoreceptors reveals similarity to IKx, a K+ current in rod inner segments.

ABSTRACT: In this study, we describe two splice variants of an ether-à-go-go (EAG) K+ channel cloned from bovine retina: bEAG1 and bEAG2. The bEAG2 polypeptide contains an additional insertion of 27 amino acids in the extracellular linker between transmembrane segments S3 and S4. The heterologously expressed splice variants differ in their activation kinetics and are differently modulated by extracellular Mg2+. Cooperativity of modulation by Mg2+ suggests that each subunit of the putative tetrameric channel binds a Mg2+ ion. The channels are neither permeable to Ca2+ ions nor modulated by cyclic nucleotides. In situ hybridization localizes channel transcripts to photoreceptors and retinal ganglion cells. Comparison of EAG currents with IKx, a noninactivating K+ current in the inner segment of rod photoreceptors, reveals an intriguing similarity, suggesting that EAG polypeptides are involved in the formation of Kx channels.

SUBMITTER: Frings S

PROVIDER: S-EPMC2217119 | biostudies-literature | 1998 Apr

REPOSITORIES: biostudies-literature

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Characterization of ether-à-go-go channels present in photoreceptors reveals similarity to IKx, a K+ current in rod inner segments.

Frings S S Brüll N N Dzeja C C Angele A A Hagen V V Kaupp U B UB Baumann A A

The Journal of general physiology 19980401 4

In this study, we describe two splice variants of an ether-à-go-go (EAG) K+ channel cloned from bovine retina: bEAG1 and bEAG2. The bEAG2 polypeptide contains an additional insertion of 27 amino acids in the extracellular linker between transmembrane segments S3 and S4. The heterologously expressed splice variants differ in their activation kinetics and are differently modulated by extracellular Mg2+. Cooperativity of modulation by Mg2+ suggests that each subunit of the putative tetrameric chann ...[more]

PMID: 9524140

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Project description:Key pointsSome ion channels are known to behave as inductors and make up the parallel resonant circuit in the plasma membrane of neurons, which enables neurons to respond to current inputs with a specific frequency (so-called 'resonant properties'). Here, we report that heterologous expression of mouse Kv11 voltage-dependent K+ channels generate resonance and oscillation at depolarized membrane potentials in HEK293 cells; expressions of individual Kv11 subtypes generate resonance and oscillation with different frequency properties. Kv11.3-expressing HEK293 cells exhibited transient conductance changes that opposed the current changes induced by voltage steps; this probably enables Kv11 channels to behave like an inductor. The resonance and oscillation of inferior olivary neurons were impaired at the resting membrane potential in Kv11.3 knockout mice. This study helps to elucidate basic ion channel properties that are crucial for the frequency responses of neurons.AbstractThe plasma membranes of some neurons preferentially respond to current inputs with a specific frequency, and output as large voltage changes. This property is called resonance, and is thought to be mediated by ion channels that show inductor-like behaviour. However, details of the candidate ion channels remain unclear. In this study, we mainly focused on the functional roles of Kv11 potassium (K+ ) channels, encoded by ether-á-go-go-related genes, in resonance in mouse inferior olivary (IO) neurons. We transfected HEK293 cells with long or short splice variants of Kv11.1 (Merg1a and Merg1b) or Kv11.3, and examined membrane properties using whole-cell recording. Transfection with Kv11 channels reproduced resonance at membrane potentials depolarized from the resting state. Frequency ranges of Kv11.3-, Kv11.1(Merg1b)- and Kv11.1(Merg1a)-expressing cells were 2-6 Hz, 2-4 Hz, and 0.6-0.8 Hz, respectively. Responses of Kv11.3 currents to step voltage changes were essentially similar to those of inductor currents in the resistor-inductor-capacitor circuit. Furthermore, Kv11 transfections generated membrane potential oscillations. We also confirmed the contribution of HCN1 channels as a major mediator of resonance at more hyperpolarized potentials by transfection into HEK293 cells. The Kv11 current kinetics and properties of Kv11-dependent resonance suggested that Kv11.3 mediated resonance in IO neurons. This finding was confirmed by the impairment of resonance and oscillation at -30 to -60 mV in Kcnh7 (Kv11.3) knockout mice. These results suggest that Kv11 channels have important roles in inducing frequency-dependent responses in a subtype-dependent manner from resting to depolarized membrane potentials.

Dataset Information

Characterization of ether-a-go-go channels present in photoreceptors reveals similarity to IKx, a K+ current in rod inner segments.

Publications

Characterization of ether-à-go-go channels present in photoreceptors reveals similarity to IKx, a K+ current in rod inner segments.

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