Molecular Determinants for Activation of G-protein-coupled Inward Rectifier K+ (GIRK) Channels by Extracellular Acidosis

Mao, Jinzhe; Li, Li; McManus, Maurine; Wu, Jianping; Cui, Ningren; Jiang, Chun

doi:10.1074/jbc.m205438200

Cited by 18 publications

(25 citation statements)

References 46 publications

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“…The higher peak-mean ratio is likely to be a result of selective enhancement of synaptic communications between the neuronal pair under the PEH study over other cells that also synapse with these neurons. The higher peak-mean ratio also can be produced by 1) more neurotransmitter release following each action potential in presynaptic neurons, and/or 2) augmentation of postsynaptic receptors by hypercapnia (Chen et al 2001;Mao et al 2002;Wemmie et al 2002). Clearly, the clarification of these issues requires direct measurements of synaptic transmission.…”

Section: Discussionmentioning

confidence: 99%

Hypercapnia modulates synaptic interaction of cultured brainstem neurons

Ling¹,

Su²,

Zhang³

et al. 2008

Respiratory Physiology & Neurobiology

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SummaryCO 2 is an important metabolic product whose concentrations are constantly monitored by CO 2 chemoreceptors. However, the high systemic CO 2 sensitivity may not be achieved by the CO 2 chemoreceptors without neuronal network processes. To show modulation of network properties during hypercapnia, we studied brainstem neurons dissociated from embryonic rats (P17-19) in multi-electrode arrays (MEA) after initial period (3 weeks) of culture. Spike trains of 33,622 pairs of units were analyzed using peri-event histograms (PEH). The amplitude of pericentral peaks between two CO 2 -stimulated units increased and the peak latency decreased during hypercapnia. Similar enhancement of synaptic strength was observed in those sharing a common input. These phenomena were not seen in CO 2 -unresponsive neurons. The amplitude of pericentral peaks between two CO 2 inhibited units also increased without changing latency. Over 60% CO 2 -stimulated neurons studied received mono-/oligosynaptic inputs from other CO 2 -stimulated cells, whereas only ~10% CO 2 -unresponsive neurons had such synaptic inputs. A small number of brainstem neurons showed electrical couplings. The coupling efficiency of CO 2 -stimulated but not CO 2 -unresponsive units was suppressed by ~50% with high PCO 2 . Inhibitory synaptic projections were also found, which was barely affected by hypercapnia. Consistent with the strengthening of excitatory synaptic connections, CO 2 sensitivity of post-synaptic neurons was significantly higher than presynaptic neurons. The difference was eliminated with blockade of presynaptic input. Based on these indirect assessments of synaptic interaction, our PEH analysis suggests that hypercapnia appears to modulate excitatory synaptic transmissions, especially those between CO 2 -stimulated neurons. KeywordsCO 2 chemoreceptor; multielectrode arrays; MEA; peri-event histogram; cross-correlation; cell culture; neuronal network; electrical coupling 1, IntroductionCO 2 is a major metabolic product and plays an important role in systemic pH regulation and acid-base secretions. The PCO 2 levels are tightly regulated by several feedback control systems in which a critical step is the CO 2 detection by sensing cells in the brainstem and carotid body (Feldman et al. 2003;Richerson 2004;Putnam et al. 2004; Guyenet et al. 2005b). Of particular interest are brainstem CO 2 -chemosensitive neurons, as the systemic CO 2 response is retained after carotid bodies are removed bilaterally. With these CO 2 -chemosensitive cells, the nervous system can detect a change in arterial PCO 2 by as low as 1 torr and couple it to a 20-30% * Correspondence to: Phone: 404-651-0913, Fax: 404-651-2509, E-mail: cjiang@gsu.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Pl...

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Section: Discussionmentioning

confidence: 99%

Hypercapnia modulates synaptic interaction of cultured brainstem neurons

Ling¹,

Su²,

Zhang³

et al. 2008

Respiratory Physiology & Neurobiology

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“…Experiments were performed as described (36). In brief, frogs were anesthetized by bathing them in distilled water containing 0.3% 3-aminobenzoic acid ethyl ester.…”

Section: Methodsmentioning

confidence: 99%

“…These cDNAs were subcloned into the eukaryotic expression vector pcDNA3.1 (Invitrogen) and used for Xenopus oocyte expression without cRNA synthesis. PCR was used to generate the GIRK1͞GIRK4 dimer (36). Site-specific mutations were made by using a site-directed mutagenesis kit (Stratagene).…”

Section: Methodsmentioning

confidence: 99%

Molecular basis for the inhibition of G protein-coupled inward rectifier K⁺channels by protein kinase C

Mao

Wang²,

Chen³

et al. 2004

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

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G protein-coupled inward rectifier K ؉ (GIRK) channels regulate cellular excitability and neurotransmission. The GIRK channels are activated by a number of inhibitory neurotransmitters through the G protein ␤␥ subunit (G␤␥) after activation of G protein-coupled receptors and inhibited by several excitatory neurotransmitters through activation of phospholipase C. If the inhibition is produced by PKC, there should be PKC phosphorylation sites in GIRK channel proteins. To identify the PKC phosphorylation sites, we performed systematic mutagenesis analysis on GIRK4 and GIRK1 subunits expressed in Xenopus oocytes. Our data showed that the heteromeric GIRK1͞GIRK4 channels were inhibited by a PKC activator phorbol 12-myristate 13-acetate (PMA) through reduction of single channel open-state probability. Direct application of the catalytic subunit of PKC to excised patches had a similar inhibitory effect. This inhibition was greatly eliminated by mutation of Ser-185 in GIRK1 and Ser-191 in GIRK4 that remained G protein sensitive. The PKC-dependent phosphorylation seems to mediate the channel inhibition by the excitatory neurotransmitter substance P (SP) as specific PKC inhibitors and mutation of these PKC phosphorylation sites abolished the SP-induced inhibition of GIRK1͞GIRK4 channels. Thus, these results indicate that the PKC-dependent phosphorylation underscores the inhibition of GIRK channels by SP, and Ser-185 in GIRK1 and Ser-191 in GIRK4 are the PKC phosphorylation sites.play an important role in controlling membrane excitability and synaptic transmission (1, 2). Four members of GIRK channels have been cloned in mammals, i.e., GIRK1 through GIRK4 (Kir3.1 through Kir3.4). These channels are expressed in the heart, brain, and endocrine tissues (3, 4). Stoichiometric studies indicate that a functional GIRK channel consists of four homomeric subunits or two pairs of heteromeric subunits (3, 4). Coassembly of GIRK1 with GIRK4 forms muscarinic receptorcoupled K ϩ channels mainly in the heart (2, 5). The GIRK channels are activated by certain inhibitory transmitters and hormones. On activation of G i/o -coupled receptors by the neurotransmitters or hormones, the G protein ␤␥ subunit (G ␤␥ ) dissociated from the heterotrimeric G ␣␤␥ directly interacts with cytosolic domains of GIRK channel proteins (6-9), and activates the channels through a mechanism that involves movement of pore-lining helices (10-12). Critical domains and amino acids have been identified to be responsible for the basal G ␤␥ -dependent and agonist-induced channel activities (6,7,13,14). Furthermore, the GIRK channel activation may rely on local phosphatidylinositol-4,5-biphosphate (PIP 2 ) in membrane microdomains (15, 16) or cytosolic Na ϩ (16,17).In addition to direct activation by G ␤␥ , GIRK channels are inhibited by a number of excitatory neurotransmitters or hormones, such as acetylcholine (18-20), thyroid-stimulating hormone (TSH)-releasing hormones (21), bombesin (22), substance P (SP) (23), and glutamate (24). These transmitters or hormones sh...

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“…For example, at the presynaptic membrane, H ϩ inhibits voltage-gated Ca 2ϩ channels to reduce vesicle release (4,6,38). At the postsynaptic membrane, H ϩ inhibits NMDA receptors (39,40) and increases the conductance of G protein-coupled inward rectifier K ϩ channels (41). In each of these cases, H ϩ modulates the functional response of ion channels to voltage or some other neurotransmitter.…”

Section: Asic1a Is a Proton Receptor At Dendritic Spinesmentioning

confidence: 99%

Acid-sensing ion channel 1a is a postsynaptic proton receptor that affects the density of dendritic spines

Zha

Wemmie

Green³

et al. 2006

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

174

256

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Extracellular proton concentrations in the brain may be an important signal for neuron function. Proton concentrations change both acutely when synaptic vesicles release their acidic contents into the synaptic cleft and chronically during ischemia and seizures. However, the brain receptors that detect protons and their physiologic importance remain uncertain. Using organotypic hippocampal slices and biolistic transfection, we found the acid-sensing ion channel 1a (ASIC1a), localized in dendritic spines where it functioned as a proton receptor. ASIC1a also affected the density of spines, the postsynaptic site of most excitatory synapses. Decreasing ASIC1a reduced the number of spines, whereas overexpressing ASIC1a had the opposite effect. Ca 2؉ -mediated Ca 2؉ ͞calmodulin-dependent protein kinase II (CaMKII) signaling was probably responsible, because acid evoked an ASIC1a-dependent elevation of spine intracellular Ca 2؉ concentration, and reducing or increasing ASIC1a levels caused parallel changes in CaMKII phosphorylation in vivo. Moreover, inhibiting CaMKII prevented ASIC1a from increasing spine density. These data indicate that ASIC1a functions as a postsynaptic proton receptor that influences intracellular Ca 2؉ concentration and CaMKII phosphorylation and thereby the density of dendritic spines. The results provide insight into how protons influence brain function and how they may contribute to pathophysiology.Ca 2ϩ ͞calmodulin-dependent protein kinase II ͉ neuron ͉ sodium channel ͉ synapse W hen synaptic vesicles fuse with the presynaptic membrane, they release neurotransmitter into the synaptic cleft and activate neurotransmitter receptors on the postsynaptic membrane. Several measurements place synaptic vesicle pH at Ϸ5.2-5.7 (1-3). As a result, when synaptic vesicles discharge their contents, the pH at synapses may fall, especially during repeated discharge with release of multiple vesicles. Accordingly, several studies have detected acidification during synaptic transmission (4-6); for example, pH in the retinal ribbon synapse is estimated to drop 0.2-0.6 pH units during synaptic transmission (4, 6). In addition to physiological acidification during neurotransmission, central pH falls in disease states such as ischemia and seizure (7). Thus, understanding how protons regulate channels and its consequence on synapses may help us better understand neuronal function and provide insight into neurological diseases where acidosis is involved.Interesting candidates for sensing protons are acid-sensing ion channels (ASICs). ASICs are activated by extracellular protons. They belong to the degenerin͞epithelial Na ϩ channel family of nonvoltage gated cation channels (8-10). Four ASIC genes (ASIC1 to ASIC4) and splice variants (a and b) for ASIC1 and ASIC2 have been identified. ASIC subunits have two transmembrane domains and a large extracellular loop, and they function as homomultimers or heteromultimers to conduct Na ϩ and Ca 2ϩ . In the peripheral nervous system, ASICs contribute to mechanosensation, nocicept...

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Molecular Determinants for Activation of G-protein-coupled Inward Rectifier K+ (GIRK) Channels by Extracellular Acidosis

Cited by 18 publications

References 46 publications

Hypercapnia modulates synaptic interaction of cultured brainstem neurons

Hypercapnia modulates synaptic interaction of cultured brainstem neurons

Molecular basis for the inhibition of G protein-coupled inward rectifier K⁺channels by protein kinase C

Acid-sensing ion channel 1a is a postsynaptic proton receptor that affects the density of dendritic spines

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Molecular Determinants for Activation of G-protein-coupled Inward Rectifier K+ (GIRK) Channels by Extracellular Acidosis

Cited by 18 publications

References 46 publications

Hypercapnia modulates synaptic interaction of cultured brainstem neurons

Hypercapnia modulates synaptic interaction of cultured brainstem neurons

Molecular basis for the inhibition of G protein-coupled inward rectifier K+channels by protein kinase C

Acid-sensing ion channel 1a is a postsynaptic proton receptor that affects the density of dendritic spines

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Molecular basis for the inhibition of G protein-coupled inward rectifier K⁺channels by protein kinase C