The G protein-gated atrial K+ channel is stimulated by three distinct GIα-subunits

Yatani, Atsuko; Mattera, Rafael; Codina, Juan; Graf, Rolf; Okabe, Kouji; Padrell, Elena; Iyengar, Ravi; Brown, Arthur M.; Birnbaumer, Lutz

doi:10.1038/336680a0

Cited by 296 publications

(75 citation statements)

References 25 publications

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“…However, little is known about the role of G␣ z in vivo and in the cells in which it is normally expressed. In contrast to G␣ z , the functional mechanism of G␣ i is well known, including inhibition of adenylyl cyclase (56), release of ␤␥ subunits (57), and interaction with ion channels (58). Northern blot and PCR analysis show that RGSZ1 is highly expressed in the caudate nucleus and the thalamus, implying that RGSZ1 may regulate GPCR and G protein signaling in these brain regions (33).…”

Section: Discussionmentioning

confidence: 99%

Regulator of G Protein Signaling Z1 (RGSZ1) Interacts with Gαi Subunits and Regulates Gαi-mediated Cell Signaling

Wang

Zhang

et al. 2002

Journal of Biological Chemistry

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Regulator of G protein signaling (RGS) proteins constitute a family of over 20 proteins that negatively regulate heterotrimeric G protein-coupled receptor signaling pathways by enhancing endogenous GTPase activities of G protein ␣ subunits. RGSZ1, one of the RGS proteins specifically localized to the brain, has been cloned previously and described as a selective GTPase accelerating protein for G␣ z subunit. Here, we employed several methods to provide new evidence that RGSZ1 interacts not only with G␣ z, but also with G␣ i , as supported by in vitro binding assays and functional studies. Using glutathione S-transferase fusion protein pulldown assays, glutathione S-transferase-RGSZ1 protein was shown to bind 35 S-labeled G␣ i1 protein in an AlF 4 ؊ dependent manner. The interaction between RGSZ1 and G␣ i was confirmed further by co-immunoprecipitation studies and yeast two-hybrid experiments using a quantitative luciferase reporter gene. Extending these observations to functional studies, RGSZ1 accelerated endogenous GTPase activity of G␣ i1 in single-turnover GTPase assays. Human RGSZ1 functionally regulated GPA1 (a yeast G␣ i -like protein)-mediated yeast pheromone response when expressed in a SST2 (yeast RGS protein) knockout strain. In PC12 cells, transfected RGSZ1 blocked mitogen-activated protein kinase activity induced by UK14304, an ␣ 2 -adrenergic receptor agonist. Furthermore, RGSZ1 attenuated D2 dopamine receptor agonist-induced serum response element reporter gene activity in Chinese hamster ovary cells. In summary, these data suggest that RGSZ1 serves as a GTPase accelerating protein for G␣ i and regulates G␣ i -mediated signaling, thus expanding the potential role of RGSZ1 in G protein-mediated cellular activities.Trimeric guanine nucleotide-binding proteins (G proteins) 1 are key components in transducing extracellular signals into intracellular responses (1-5). The functional activity of G protein ␣ subunit is critically governed by the rates of GDP/GTP exchange stimulated by the receptor activation, and the intrinsic GTPase activity that hydrolyzes the GTP to GDP. However, the in vitro measured intrinsic GTPase activity of G protein ␣ subunits is too slow to account for the rapid signal termination that occurs in vivo. A new family of proteins, regulators of G protein signaling (RGS), have been identified to accelerate the intrinsic GTPase activity of G␣ subunits and mechanistically impact the kinetics of G protein physiological function (6 -12). To date, over 20 mammalian proteins are known to contain the RGS domain, a homologous core domain of 120 amino acids. The RGS domain-containing proteins dramatically enhance the endogenous GTPase activity of G␣ subunits by binding to and stabilizing the flexible switch regions of G␣ to resemble that of the transition state, thereby lowering the activation energy barrier of the hydrolysis reaction (13-16). RGS proteins have been shown to play an essential role in desensitizing and negatively regulating G protein-mediated responses or accelerating the k...

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Section: Discussionmentioning

confidence: 99%

Regulator of G Protein Signaling Z1 (RGSZ1) Interacts with Gαi Subunits and Regulates Gαi-mediated Cell Signaling

Wang

Zhang

et al. 2002

Journal of Biological Chemistry

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“…These may be 'true' ROCs, i.e. the receptor is an integral part of the channel (as in nicotinic receptors) or uses a guanine nucleotidebinding protein as an intermediary (as has been demonstrated by Birnbaumer and his collaborators [22] for ACh-activated potassium channels in the heart). On the other hand, these channels may be activated by IP3 and/or its metabolites.…”

Section: Discussionmentioning

confidence: 99%

Extracellular calcium participates in responses to acetylcholine in Xenopus oocytes

1990

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We tested the contribution of extracellular calcium (Ca,Z') to membrane electrical responses to acetylcholine (ACh) in native Xenopus oocytes. Removal of Ca, caused a decrease in both the rapid (D,) and the slow (D,) chloride currents that comprise the common depolarizing response to ACh in native oocyte. The effect of Caz' removal on the muscarinic response was mimicked by the addition of 1 mM Mn2+, an effective antagonist of calcium influx, though not by antagonists of voltage-sensitive calcium channels. When oocytes were challenged with ACh in Cazf-free medium, subsequent addition of 1.8 mM CaCI, resulted in a rapid, often transient, depolarizing current. Similarly to the Cai+-dependent component of membrane electrical responses, the Ca2' 2+ -evoked current was reversibly abolished by Mn , though not by antigonists of voltage-sensitive calcium channels. Depletion of cellular calcium potentiated the Caz+ -evoked current, implying negative feedback of calcium channels by calcium. Injection of l&l00 fmol of inositol 1,4,5-trisphosphate (IP,) resulted in a two-component depolarizing current. IP, injection promoted the appearance of Ca,2+-evoked current that was significantly potentiated by previous calcium depletion. We suggest that activation of cell-membrane muscarinic receptors causes opening of apparently voltage-insensitive and verapamil or diltiazem-resistant calcium channels. These channels may be activated by IP, or its metabolites, which increase following the activation of cell membrane receptors coupled to a phospholipase C. The channels may be identical to receptor-operated channels described in other model systems.

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“…However, a long-standing controversy exists as to which G-protein subunit couples to the KG channel. Purified fBy subunit complexes (10,11) and a subunits of the Gi family (6,7,12) activation by G proteins (18-22). The similarity of the channels and of the signaling pathways in atrium and some nerve-cell preparations was strengthened by the demonstration of the coupling of a neuronal 5HT1A receptor (5HT1A-R), transiently expressed in atrial myocytes, to the atrial KG channels (23).…”

Section: Introductionmentioning

confidence: 99%

Expression of an atrial G-protein-activated potassium channel in Xenopus oocytes.

Dascal

Lim²,

Schultze-Seemann³

et al. 1993

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

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Injection of rat atrial RNA into Xenopus oocytes resulted in the expression of a guanine nucleotide binding (G) protein-activated K+ channel. Current through the channel could be activated by acetylcholine or, if RNA encoding a neuronal SHT1A receptor was coinjected with atrial RNA, by serotonin (5HT). A 5HT-evoked current (ISHT) Xenopus oocytes may be employed for cloning of the G-proteinactivated K+ channel cDNA and for studying the coupling between this channel and G proteins.Parasympathetic regulation of the rate of heart contraction is exerted through the release of acetylcholine (ACh), which opens a K+ channel in the atrium and thus slows the rate of depolarization that leads to initiation of the action potential (1, 2). The coupling between binding of ACh to a muscarinic receptor and opening ofthe K+ channel occurs via a pertussis toxin (PTX)-sensitive heterotrimeric guanine nucleotide binding (G) protein, Gk (3)(4)(5), probably belonging to the inhibitory G-protein Gi family (6,7). Activation of this G-protein-activated K+ (KG) channel by Gk does not require cytoplasmic intermediates (for review, see refs. 8 and 9). However, a long-standing controversy exists as to which G-protein subunit couples to the KG channel. Purified fBy subunit complexes (10,11) and a subunits of the Gi family (6,7,12) activation by G proteins (18-22). The similarity of the channels and of the signaling pathways in atrium and some nerve-cell preparations was strengthened by the demonstration of the coupling of a neuronal 5HT1A receptor (5HT1A-R), transiently expressed in atrial myocytes, to the atrial KG channels (23). By electrophysiological and pharmacological criteria, the atrial KG channel belongs to a family of inward rectifiers that conduct K+ much better in the inward than the outward direction, are blocked by extracellular Na+, Cs+, and Ba2+, and are believed to possess a single-file pore with several permeant and blocking ion binding sites (24). Many inward rectifiers are not activated by transmitters or voltage but seem to be constitutively active. Inward rectification of the atrial KG channel is due to a block of K+ efflux by intracellular Mg2+ (25), but for some channels of this family inward rectification may not depend on the Mg2+ block (26, 27). The molecular structures of atrial and neuronal KG channels are unknown. Inwardly rectifying K+ channels structurally similar to voltage-activated K+ channels have been cloned from plant cells (28,29). Recently, the primary structures of two mammalian inward-rectifier channels have been elucidated by molecular cloning of their cDNAs via expression in Xenopus oocytes: an ATP-regulated K+ channel from kidney, ROMK1 (30), and an inward rectifier from a macrophage cell line, IRK1 (31). Both appear to belong to a superfamily of K+ channels, with only two transmembrane domains per subunit and a pore region homologous to that of K+, Ca2 , and Na+ voltage-dependent channels (see ref. 32). It has been hypothesized that the structure of G-protein-activated inwardly rectify...

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The G protein-gated atrial K+ channel is stimulated by three distinct GIα-subunits

Cited by 296 publications

References 25 publications

Regulator of G Protein Signaling Z1 (RGSZ1) Interacts with Gαi Subunits and Regulates Gαi-mediated Cell Signaling

Regulator of G Protein Signaling Z1 (RGSZ1) Interacts with Gαi Subunits and Regulates Gαi-mediated Cell Signaling

Extracellular calcium participates in responses to acetylcholine in Xenopus oocytes

Expression of an atrial G-protein-activated potassium channel in Xenopus oocytes.

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