Cloning of a Xenopus laevis Inwardly Rectifying K+ Channel Subunit That Permits GIRK1 Expression of IKACh Currents in Oocytes

Hedin, Karen E.; Lim, Nancy; Clapham, David E.

doi:10.1016/s0896-6273(00)80060-4

Cited by 174 publications

(168 citation statements)

References 25 publications

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“…Homomeric assembly of either subunit alone was not sufficient to produce KACh currents. GIRK4 channels gave rise to currents with properties distinct from those of Ia-ACh (Krapivinsky et al, 1995;Chan et al, 1996), while GIRK1 required coassembly with a native oocyte "GIRK4-1ike" subunit (GIRK5 or XIR) in order to produce functional channels (Hedin et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

Na+ activation of the muscarinic K+ channel by a G-protein-independent mechanism.

Sui

Chan

Logothetis

1996

The Journal of General Physiology

124

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Muscarinic potassium channels (KAch) are composed of two subunits, GIRK1 and GIRK4 (or CIR), and are directly gated by G proteins. We have identified a novel gating mechanism of KAC h, independent of G-protein activation. This mechanism involved functional modification of KACh which required hydrolysis of physiological levels of intracellular ATP and was manifested by an increase in the channel mean open time. The ATP-modifled channels could in turn be gated by intracellular Na +, starting at ~3 mM with an ECs0 of ~40 raM. The Na+-gating of KAC h was operative both in native atrial cells and in a heterologous system expressing recombinant channel subunits. Block of the Na+/K + pump (e.g., by cardiac glycosides) caused significant activation of KAC h in atrial cells, with a time course similar to that of Na + accumulation and in a manner indistinguishable from that of Na+-mediated activation of the channel, suggesting that cardiac glycosides activated KACh by increasing intracellular Na + levels. These results demonstrate for the first time a direct effect of cardiac glycosides on atrial myocytes involving ion channels which are critical in the regulation of cardiac rhythm.

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Section: Introductionmentioning

confidence: 99%

Na+ activation of the muscarinic K+ channel by a G-protein-independent mechanism.

Sui

Chan

Logothetis

1996

The Journal of General Physiology

124

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“…Moreover, radiolabeled proteins were not precipitated when the antibody was blocked with the specific channel peptide (data not shown). p43 appears to be an endogenous GIRK4-like channel that forms heteromers with GIRK1 (21), and this channel has been cloned and characterized (23). In G4ϩG1 cRNA-coinjected oocytes, G1-Ab precipitated a 45-kDa band (p45) that corresponds to the exogenous GIRK4 protein (Fig.…”

Section: Glycosylation Sites On Inward Rectifier Kmentioning

confidence: 99%

“…Expression of only GIRK1 resulted in appreciable N-glycosylation (Fig. 3A, lane 5), but endogenous oocyte GIRK4 expression and heteromeric formation may promote this (23,45).…”

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confidence: 98%

Glycosylation of GIRK1 at Asn119 and ROMK1 at Asn117 Has Different Consequences in Potassium Channel Function

Pabon

Chan

Sui³

et al. 2000

Journal of Biological Chemistry

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GIRK (G protein-gated inward rectifier K؉ channel) proteins play critical functional roles in heart and brain physiology. Using antibodies directed to either GIRK1 or GIRK4, site-directed mutagenesis, and specific glycosidases, we have investigated the effects of glycosylation in the biosynthesis and heteromerization of these proteins expressed in oocytes. Both GIRK1 and GIRK4 have one extracellular consensus N-glycosylation site. Using chimeras between GIRK1 and GIRK4 as well as a GIRK1 N-glycosylation mutant, we report that GIRK1 was glycosylated at Asn 119 , whereas GIRK4 was not glycosylated at Asn 132 . GIRK1 membrane-spanning domain 1 was required for optimal glycosylation at Asn 119 because a chimera that contained GIRK4 membrane-spanning domain 1 significantly reduced the addition of a carbohydrate structure at this site. This finding may partly account for the reason that GIRK4 is not glycosylated at Asn 132 , either as a homomer or when coexpressed with GIRK1. When the GIRK1(N119Q) mutant was coexpressed with GIRK4, the biophysical properties of the heteromeric channel and the magnitude of the agonist-induced currents were similar to those of controls. Thus, N-glycosylation of GIRK1 at Asn 119 does not appear to affect its physical association with GIRK4, the routing of the heteromer to the cell surface, or heteromeric channel function, unlike the dramatic functional effects of N-glycosylation of ROMK1 at Asn

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“…G protein-gated inward rectifier K ϩ channels (GIRKs) expressed in neuronal, atrial, and other cell types are formed by subunits encoded by a five-membered gene subfamily (K ir 3.0), and are activated by neuromodulators acting on G proteincoupled receptors (1,2). Although GIRKs are inward rectifiers, their usual physiological role is to permit an outward K ϩ current near resting membrane potentials (E M ; ref.…”

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confidence: 99%

“…GIRKs normally function as heterotetrameric channels of two or more subunit isoforms (2,(7)(8)(9)(10). The isoforms GIRK1-3 and, to a lesser extent, GIRK4 are expressed in CA1-CA3 pyramidal and dentate gyrus granule cells of the rat hippocampus (10,11), where GIRK-type K ϩ currents have previously been described (e.g., refs.…”

mentioning

confidence: 99%

Activation of heteromeric G protein-gated inward rectifier K ⁺ channels overexpressed by adenovirus gene transfer inhibits the excitability of hippocampal neurons

Ehrengruber

Doupnik

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

103

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G protein-gated inward rectifier K ؉ channel subunits 1-4 (GIRK1-4) have been cloned from neuronal and atrial tissue and function as heterotetramers. To examine the inhibition of neuronal excitation by GIRKs, we overexpressed GIRKs in cultured hippocampal neurons from 18 day rat embryos, which normally lack or show low amounts of GIRK protein and currents. Adenoviral recombinants containing the cDNAs for GIRK1, GIRK2, GIRK4, and the serotonin 1A receptor were constructed. Typical GIRK currents could be activated by endogenous GABA B , serotonin 5-HT 1A , and adenosine A1 receptors in neurons coinfected with GIRK1؉2 or GIRK1؉4. Under current clamp, GIRK activation increased the cell membrane conductance by 1-to 2-fold, hyperpolarized the cell by 11-14 mV, and inhibited action potential firing by increasing the threshold current for firing by 2-to 3-fold. These effects were not found in non-and mock-infected neurons, and were similar to the effects of muscarinic stimulation of native GIRK currents in atrial myocytes. Two inhibitory effects of GIRK activation, hyperpolarization and diminution of depolarizing pulses, were simulated from the experimental data. These inhibitory effects are physiologically important in the voltage range between the resting membrane potential and the potential where voltage-gated Na ؉ and K ؉ currents are activated; that is where GIRK currents are outward.

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Cloning of a Xenopus laevis Inwardly Rectifying K+ Channel Subunit That Permits GIRK1 Expression of IKACh Currents in Oocytes

Cited by 174 publications

References 25 publications

Na+ activation of the muscarinic K+ channel by a G-protein-independent mechanism.

Na+ activation of the muscarinic K+ channel by a G-protein-independent mechanism.

Glycosylation of GIRK1 at Asn119 and ROMK1 at Asn117 Has Different Consequences in Potassium Channel Function

Activation of heteromeric G protein-gated inward rectifier K ⁺ channels overexpressed by adenovirus gene transfer inhibits the excitability of hippocampal neurons

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Cloning of a Xenopus laevis Inwardly Rectifying K+ Channel Subunit That Permits GIRK1 Expression of IKACh Currents in Oocytes

Cited by 174 publications

References 25 publications

Na+ activation of the muscarinic K+ channel by a G-protein-independent mechanism.

Na+ activation of the muscarinic K+ channel by a G-protein-independent mechanism.

Glycosylation of GIRK1 at Asn119 and ROMK1 at Asn117 Has Different Consequences in Potassium Channel Function

Activation of heteromeric G protein-gated inward rectifier K + channels overexpressed by adenovirus gene transfer inhibits the excitability of hippocampal neurons

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Activation of heteromeric G protein-gated inward rectifier K ⁺ channels overexpressed by adenovirus gene transfer inhibits the excitability of hippocampal neurons