Evidence that Neuronal G-Protein-Gated Inwardly Rectifying K^+ Channels are Activated by Gbetagamma Subunits and Function as Heteromultimers

Division of Biology, California Institute of Technology, Pasadena 91225, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 07/1995; 92(14):6542-6546. DOI: 10.1073/pnas.92.14.6542
Source: PubMed


Guanine nucleotide-binding proteins (G proteins) activate K^+ conductances in cardiac atrial cells to slow heart rate and in neurons to decrease excitability. cDNAs encoding three isoforms of a G-protein-coupled, inwardly rectifying K^+ channel (GIRK) have recently been cloned from cardiac (GIRK1/Kir 3.1) and brain cDNA libraries (GIRK2/Kir 3.2 and GIRK3/Kir 3.3). Here we report that GIRK2 but not GIRK3 can be activated by G protein subunits Gbeta_1 and Ggamma_2 in Xenopus oocytes. Furthermore, when either GIRK3 or GIRK2 was coexpressed with GIRK1 and activated either by muscarinic receptors or by Gbetagamma subunits, G-protein-mediated inward currents were increased by 5- to 40-fold. The single-channel conductance for GIRK1 plus GIRK2 coexpression was intermediate between those for GIRK1 alone and for GIRK2 alone, and voltage-jump kinetics for the coexpressed channels displayed new kinetic properties. On the other hand, coexpression of GIRK3 with GIRK2 suppressed the GIRK2 alone response. These studies suggest that formation of heteromultimers involving the several GIRKs is an important mechanism for generating diversity in expression level and function of neurotransmitter-coupled, inward rectifier K^+ channels.

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    • "On the other hand, it has been previously shown that expression of either Kir3.1 or Kir3.4 homomers fails to display similar channel activity as the heteromeric complex. Specifically, homomeric expression of Kir3.1 in several mammalian cell lines does not yield detectable currents (e.g., [15] [27] [29]). Furthermore, homomeric expression of Kir3.4 gives several-fold smaller currents than the Kir3.1/Kir3.4 "
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    ABSTRACT: Cholesterol is one of the major lipid components of membranes in mammalian cells. In recent years, cholesterol has emerged as a major regulator of ion channel function. The most common effect of cholesterol on ion channels in general and on inwardly rectifying potassium (Kir) channels in particular is a decrease in activity. In contrast, we have recently shown that native G-protein gated Kir (GIRK or Kir3) channels that underlie atrial KACh currents are up-regulated by cholesterol. Here we unveil the biophysical basis of cholesterol-induced increase in KACh activity. Using planar lipid bilayers we show that cholesterol significantly enhances the channel open frequency of the Kir3.1/Kir3.4 channels, which underlie KACh currents. In contrast, our data indicate that cholesterol does not affect their unitary conductance. Furthermore, using fluorescent and TIRF microscopy as well as surface protein biotinylation, we also show that cholesterol enrichment in vitro has no effect on surface expression of GFP-tagged channels expressed in Xenopus oocytes or transfected into HEK293 cells. Together, these data demonstrate for the first time that cholesterol enhances Kir3-mediated current by increasing the channel open probability. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta 07/2015; 1848(10 Pt A). DOI:10.1016/j.bbamem.2015.07.007 · 4.66 Impact Factor
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    • "In addition, we demonstrated that 5-HT 1A –5-HT 7 heterodimerization markedly decreases the ability of 5-HT 1A receptor to activate GIRK channels, an effect mediated through the Gbc subunits of inhibitory G proteins (Reuveny et al., 1994; Kofuji et al., 1995). The finding that pharmacological blockade of 5-HT 7 receptor does not overcome this inhibitory effect suggests that direct receptor–receptor interaction rather than 5- HT 7 -receptor-mediated signalling is responsible for the reduced GIRK channel activation. "
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    Journal of Cell Science 02/2012; 125(Pt 10):2486-99. DOI:10.1242/jcs.101337 · 5.43 Impact Factor
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    • "Four GIRK channel isoforms (Kir3.1 – Kir3.4) associate into various homo/heterotetrameric complexes. GIRK2 (Kir3.2) forms functional homotetramers and is thus a good candidate for crystallographic structure determination (Kofuji et al., 1995). To obtain suitably diffracting crystals, we modified the mouse GIRK2 cDNA to remove unstructured regions of the N-and C-termini (Nishida et al., 2007; Nishida and MacKinnon, 2002; Pegan et al., 2005; Tao et al., 2009). "
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