共查询到20条相似文献,搜索用时 15 毫秒
1.
Nicholas S. Berrow Roger D. Hurst Susan L. F. Chan Noel G. Morgan 《Bioscience reports》1992,12(2):95-100
Rat islets express a pertussis toxin sensitive G-protein involved in receptor-mediated inhibition of insulin secretion. This
has been assumed previously to represent “Gi” which couples inhibitory receptors to adenylate cyclase. Incubation of islet G-proteins with32P-NAD and pertussis toxin resulted in the labelling of a band of molecular weight 40,000. This band was very broad and did
not allow resolution of individual components. Incubation of the radiolabelled proteins with an anti-Go antiserum resulted in specific immunoprecipitation of a32P-labelled band. These results demonstrate that the complement of pertussis toxin sensitive G-proteins in rat islets includes
Go. 相似文献
2.
Clark GD Zorumski CF McNeil RS Happel LT Ovella T McGuire S Bix GJ Swann JW 《Neurochemical research》2000,25(5):603-611
In most nonneural systems, platelet-activating factor (PAF) receptor effects are mediated by G-proteins that are often pertussis toxin-sensitive. The activation of pertussis toxin-sensitive G-proteins linked to PAF receptors results in the mobilization of intracellular calcium, at least in part, through the second messenger inositol triphosphate. We have sought to determine if a pertussis toxin-sensitive G-protein is involved in the PAF receptor-mediated phenomena of growth cone collapse and of synaptic enhancement in primary neuronal culture. Using infrared differential interference contrast microscopy and patch-clamp recording techniques, pertussis toxin, but not the inactive B oligomer of the toxin, was found to block both the growth cone collapse and the enhanced synaptic release of excitatory transmitter induced by a nonhydrolyzable PAF receptor agonist, making it likely that Go, Gq, or Gi is the G-protein transducer of PAF receptors in primary neurons. We believe that PAF acts directly on neuronal receptors, which are linked to pertussis toxin-sensitive G-proteins, on the tips of developing neurites, and on presynaptic nerve terminals, leading to growth cone collapse and enhanced synaptic release of transmitter. 相似文献
3.
In order to study the mechanism and regulation of K+ resorption from the xylem by the cells that border the xylem vessels (the xylem parenchyma cells), K+ inward-rectifying channels (KIRCs) in the plasma membrane of xylem parenchyma cells from Hordeum vulgare L. cv. Apex were studied using the patch-clamp technique. In the inside-out configuration, three different types of K+ channel and a further K+ conductance could be identified. Two of these channels, named KIRC1 and KIRC2, were activated by guanosine 5′-[β,γ-imido]triphosphate
(Gpp(NH)p; 150 μM), a non-hydrolyzable derivative of GTP, indicating that channel activity was up-regulated by G-proteins;
modulation of channel activity occurred via a membrane-delimited pathway, since the effect could be demonstrated in cell-free
patches. At 100 mM external K+, KIRC1 had a conductance of 8 pS. There was no effect of ATP on channel activity. Likewise, addition of 150 μM guanosine
5′-[β-thio]diphosphate (GDPβS) or adenosine 5′-[γ-thio]triphosphate (ATPγS) failed to activate KIRC1, indicating nucleotide
specificity of the effect. A second K+ channel, activated by Gpp(NH)p (KIRC2) with gating properties clearly different from the first one was less frequently observed.
Four different substates could be identified; the main level had a conductance of about 2 pS. Gating below the Nernst potential
of K+ (EK) was voltage-independent. The channel closed at potentials more positive than EK. A third, hyperpolarization-activated K+ channel, KIRC3, with a low open probability was encountered in inside-out patches. It had a conductance of 45 pS in 100 mM
K+. Channel activity was not affected by the addition of G-protein modulators. Moreover, slowly activating inward currents carried
by K+ were recorded in several patches that are ascribed to a `subpicosiemens conductance'. Neither GDPβS nor Gpp(NH)p appeared
to have an effect on the currents. Whole-cell measurements with these G-protein modulators included in the pipette solution
were in general agreement with the results obtained on cell-free patches. A statistical evaluation revealed that time-dependent
inward currents were larger when the G-protein activator Gpp(NH)p was included in the pipette medium compared to measurements
with the inhibitor GDPβS. With the GTP analogue, an additional instantaneous component was elicited that was ascribed to KIRC2
activity. Data are discussed with respect to the putative role of G-proteins in conveying hormonal signals. Regulation by
G-protein may either serve to fine-tune K+ uptake by xylem parenchyma cells or to initiate depolarization, followed by salt-efflux through depolarization-activated
cation and anion channels.
Received 11 October 1996 / Accepted: 21 April 1997 相似文献
4.
Extracellular signals are transduced across the cell by the cell surface receptors, with the aid of G-proteins, which act
at a critical point of signal transduction and cellular regulation. Structurally, G-proteins are heterotrimeric consisting
α, β and γ subunits but in functionally active state they dissociate into α subunit coupled to GTP and as βγ dimer. G-proteins
can be broadly divided into two classes based on their sensitivity to pertussis toxin and cholera toxin. Existence of various
forms of each of the subunit allows molecular diversity in the subunit species of G-proteins. These subunits interact with
a wide range of receptors and effectors, facilitated by post translational modification of their subunits. Different types
of G-proteins mediate several signalling events in different parts of the body. This review summarizes the features of (i)
structural and functional heterogenity among different subunits of G-proteins, (ii) interaction of G-proteins and their subunits
with effectors with specific cases of G-protein mediated signalling in olfaction, phototransduction in the retina,
ras andras
related transduction and (iii) disease conditions associated with malfunctioning of G-proteins. 相似文献
5.
The involvement of multiple G-proteins in parathyroid hormone regulation of acid production was demonstrated in a highly enriched osteoclast population. Osteoclasts were isolated from the endosteum of 2.5 to 3-week-old chicken tibia using sequential enzymatic digestion. Single cell analysis of acid production was accomplished using microscope photometry and vital staining with acridine orange, a hydrogen ion concentration sensitive fluorescent dye. Lithium chloride, an uncoupler of G-proteins from their respective receptors, blocked parathyroid hormone stimulated production of acid. Cholera toxin, which permanently activates Gs-proteins, mimicked PTH stimulation. Pertussis toxin, which prevents receptor interaction with Gi- and Go-proteins, blocked both 10 8 M and 10 11 M PTH stimulated acid production, suggesting that the pertussis toxin-sensitive G-protein is utilized at both PTH concentrations. Immunoblots of osteoclast plasma membrane proteins, using a panel of antibodies generated against specific G-protein α subunits, revealed a 48 kDa Gsα, a 41 Goα, a 34 kDa Giα-3, and a unique 68 kDa Gα subunit, with the 41 kDa and 34 kDa bands being the most intense. Immunoblots of osteoblast plasma membrane proteins had a substantially different profile with the most intense bands being a Gsα (48 kDa) and a Goα (36 and 38 kDa). The studies suggest the utilization of at least two different G-proteins in the parathyroid hormone regulation of acid formation by osteoclasts, a Gs and a pertussis toxin-sensitive G-protein (Go and/or Giα-3). J. Cell. Biochem. 64:161–170. © 1997 Wiley-Liss, Inc. 相似文献
6.
O'Halloran DM Fitzpatrick DA McCormack GP McInerney JO Burnell AM 《Journal of molecular evolution》2006,63(1):87-94
In animal olfactory systems, odorant molecules are detected by olfactory receptors (ORs). ORs are part of the G-protein-coupled
receptor (GPCR) superfamily. Heterotrimeric guanine nucleotide binding G-proteins (G-proteins) relay signals from GPCRs to
intracellular effectors. G-proteins are comprised of three peptides. The G-protein α subunit confers functional specificity
to G-proteins. Vertebrate and insect Gα-subunit genes are divided into four subfamilies based on functional and sequence attributes.
The nematode Caenorhabditis elegans contains 21 Gα genes, 14 of which are exclusively expressed in sensory neurons. Most individual mammalian cells express multiple
distinct GPCR gene products, however, individual mammalian and insect olfactory neurons express only one functional odorant
OR. By contrast C. elegans expresses multiple ORs and multiple Gα subunits within each olfactory neuron. Here we show that, in addition to having at
least one member of each of the four mammalian Gα gene classes, C. elegans and other nematodes also possess two lineage-specific Gα gene expansions, homologues of which are not found in any other
organisms examined. We hypothesize that these novel nematode-specific Gα genes increase the functional complexity of individual
chemosensory neurons, enabling them to integrate odor signals from the multiple distinct ORs expressed on their membranes.
This neuronal gene expansion most likely occurred in nematodes to enable them to compensate for the small number of chemosensory
cells and the limited emphasis on cephalization during nematode evolution.
[Reviewing Editor: Dr. John Oakeshott]
Damien M. O’Halloran and David A. Fitzpatrick contributed equally to this work. 相似文献
7.
Other than the fact that the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel can be activated by cAMP dependent kinase (PKA), little is known about the signal transduction pathways regulating
CFTR. Since G-proteins play a principal role in signal transduction regulating several ion channels [4, 5, 9], we sought to
test whether G-proteins control CFTR Cl− conductance (CFTR G
Cl
) in the native sweat duct (SD). We permeabilized the basolateral membrane with α-toxin so as to manipulate cytosolic nucleotides.
We activated G-proteins and monitored CFTR G
Cl
activity as described earlier [20, 23, 25]. We now show that activating G-proteins with GTP-γ-S (100 μm) also activates CFTR G
Cl
in the presence of 5 mm ATP alone (without exogenous cAMP). GTP-γ-S increased CFTR G
Cl
by 44 ± 20 mS/cm2 (mean ±se; n= 7). GDP (10 mm) inhibited G-protein activation of CFTR G
Cl
even in the presence of GTP-γ-S. The heterotrimeric G-protein activator (AlF4
−) in the cytoplasmic bath activated CFTR G
Cl
(increased by 51.5 ± 9.4 mS/cm2 in the presence of 5 mm ATP without cAMP, n= 6), the magnitude of which was similar to that induced by GTP-γ-S. Employing immunocytochemical-labeling techniques, we
localized Gαs, Gαi, Gαq, and Gβ at the apical membranes of the sweat duct. Further, we showed that the mutant CFTR G
Cl
in ducts from cystic fibrosis (CF) subjects could be partially activated by G-proteins. The magnitude of mutant CFTR G
Cl
activation by G-proteins was smaller as compared to non-CF ducts but comparable to that induced by cAMP in CF ducts. We conclude
that heterotrimeric G-proteins are present in the apical membrane of the native human sweat duct which may help regulate salt
absorption by controlling CFTR G
Cl
activity.
Received: 9 June 2000/Revised: 5 October 2000 相似文献
8.
Andreas Janshoff Claudia Steinem Manfred Sieber A. el Bayâ Marcus Alexander Schmidt H.-J. Galla 《European biophysics journal : EBJ》1997,26(3):261-270
The binding of cholera toxin, tetanus toxin and pertussis toxin to ganglioside containing solid supported membranes has been
investigated by quartz crystal microbalance measurements. The bilayers were prepared by fusion of phospholipid-vesicles on
a hydrophobic monolayer of octanethiol chemisorbed on one gold electrode placed on the 5 MHz AT-cut quartz crystal. The ability
of the gangliosides GM1, GM3, GD1a, GD1b, GT1b and asialo-GM1 to act as suitable receptors for the different toxins was tested by measuring the changes of quartz resonance frequencies.
To obtain the binding constants of each ligand-receptor-couple Langmuir-isotherms were successfully fitted to the experimental
adsorption isotherms. Cholera toxin shows a high affinity for GM1 (Ka = 1.8 ⋅ 108M–1), a lower one for asialo-GM1 (Ka = 1.0 ⋅ 107 M–1) and no affinity for GM3. The C-fragment of tetanus toxin binds to ganglioside GD1a, GD1b and GT1b containing membranes with similar affinity (Ka∼106 M–1), while no binding was observed with GM3. Pertussis toxin binds to membranes containing the ganglioside GD1a with a binding constant of Ka = 1.6 ⋅ 106 M–1, but only if large amounts (40 mol%) of GD1a are present. The maximum frequency shift caused by the protein adsorption depends strongly on the molecular structure of
the receptor. This is clearly demonstrated by an observed maximum frequency decrease of 99 Hz for the adsorption of the C-fragment
of tetanus toxin to GD1b. In contrast to this large frequency decrease, which was unexpectedly high with respect to Sauerbrey's equation, implying
pure mass loading, a maximum shift of only 28 Hz was detected after adsorption of the C-fragment of tetanus toxin to GD1a.
Received: 14 January 1997 / Accepted: 15 April 1997 相似文献
9.
The human formyl peptide receptor like 1 (FPRL-1) is a variant of the Gi-coupled formyl-peptide receptor. Functional FPRL-1 is endogenously expressed in the U87 astrocytoma cell line and there is
accumulating evidence to suggest that FPRL-1 may be involved in neuroinflammation associated with the pathogenesis of Alzheimer’s
disease. In this study, we examined the ability of FPRL-1 to mobilize intracellular Ca2+ in U87 astrocytoma cells, as well as in Chinese hamster ovary (CHO) cells stably expressing FPRL-1. We showed that Trp–Lys–Tyr–Met–Val–Met–NH2 (WKYMVM), a specific agonist for FPRL-1, stimulated Ca2+ influx in both U87 and FPRL-1/CHO cells. These effects can be inhibited by the FPRL-1 selective antagonist, WRW4. Involvement of Gi proteins was demonstrated with the use of pertussis toxin, while inhibitors of store-operated channels (SOC) including 1-[2-(4-methoxyphenyl)]-2-[3-(4-methpxyphenyl)propoxy]ethyl-1H-imidazole hydrochloride (SKF96365) and 2-aminoethoxydiphenyl borate (2-APB) were found to abolish the WKYMVM-induced Ca2+ increase. However, intracellular Ca2+ mobilization in both cell lines were unaffected by the phospholipase Cβ inhibitor U73122 or selective ryanodine receptor
inhibitors. Our data demonstrated that activation of Gi-coupled FPRL-1 can lead to Ca2+ influx possibly via SOCs in U87 and FPRL-1/CHO cells. 相似文献
10.
Oocyte maturation (OM) is initiated in lower vertebrates and echinoderms when maturation-inducing substances (MIS) bind oocyte membrane receptors. This study tested the hypothesis that activation of a Gi protein is necessary for MIS-mediated OM in spotted seatrout. Addition of MIS significantly decreased adenylyl cyclase activity in a steroid specific, pertussis toxin (PTX)-sensitive manner in oocyte membranes and microinjection of PTX into oocytes inhibited MIS-induced OM, suggesting the steroid activates a Gi protein. MIS significantly increased [35S]GTPγS binding to ovarian membranes, confirming that MIS receptor binding activates a G-protein, and immunoprecipitation studies showed the increased [35S]GTPγS binding was associated with Gαi1-3 proteins. Radioligand binding studies in ovarian membranes using GTPγS and PTX demonstrated that the MIS binds a receptor coupled to a PTX-sensitive G-protein. This study provides the first direct evidence in a vertebrate model that MIS-induced activation of a Gi protein is necessary for OM. These results support a mechanism of MIS action involving binding to a novel, G-protein coupled receptor and activation of an inhibitory G-protein, the most comprehensive and plausible model of MIS initiation of OM proposed to date. 相似文献
11.
Fujita H Kato T Watanabe N Takahashi T Kitagawa S 《Archives of biochemistry and biophysics》2011,(1):121-60
Calpain inhibitors induce pertussis toxin (PTx)-sensitive chemotaxis in human neutrophils and monocytes. Here, we show that various calpain inhibitors (PD150606, PD151746, N-acetyl-Leu-Leu-Nle-CHO [ALLN], N-acetyl-Leu-Leu-Met-CHO [ALLM], and calpeptin) and γ-secretase inhibitor I induced PTx-sensitive increase in cytoplasmic free Ca2+ ([Ca2+]i) in human neutrophils and neutrophil migration. HEK-293 cells stably expressing human formyl peptide receptor (hFPR) or hFPR-like 1 (hFPRL1) displayed stimulus-specific increase in [Ca2+]i in response to calpain inhibitors (PD150606, PD151746, ALLN, ALLM, MG-132, and calpeptin), γ-secretase inhibitor I, and N-formyl-Met-Leu-Phe. Parent HEK-293 cells also displayed PTx-sensitive increase in [Ca2+]i in response to calpeptin and γ-secretase inhibitor I, whereas they displayed PTx-resistant increase in [Ca2+]i in response to MG-132. MDL-28170 induced neither an increase in [Ca2+]i in neutrophils and HEK-293 cells nor neutrophil migration. Ionomycin-induced cleavage of talin (a substrate of calpain) in neutrophils was inhibited by all inhibitors used here. These findings suggest that potent calpain inhibitors could stimulate phagocyte functions via activation of hFPR, hFPRL1 and/or other G-protein coupled receptors depending on the inhibitors used. 相似文献
12.
Iliyana V. Sazdova Bilyana M. Ilieva Ignat B. Minkov Rudolf Schubert Hristo S. Gagov 《Central European Journal of Biology》2009,4(3):327-334
The aim of this study is to investigate the mechanism of positive inotropic effect of obestatin on in vitro heart preparations of Rana ridibunda frog. The application of increasing amounts of obestatin in the concentration range from 1 μmol/l to 1 μmol/l significantly
enhances the force of contraction of excised and cannulated frog hearts. This effect was partially reduced in the presence
of prazosin (3 μmol/l). Propranolol (30 μmol/l), pertussis toxin (2 ng/ml) and the specific inhibitor of cAMP-dependent protein
kinase (PKA) Rp-adenosine 3′,5′-cyclic monophosphothioate triethylamine (30 μmol/l) completely blocked the obestatin-induced
increase of the force of frog heart contractions. It is concluded that, via its receptor molecule, obestatin activates neuronal pertussis toxin sensitive G-protein(s) that further enhance the secretion
of epinephrine from sympathetic neurons. This epinephrine activates mainly the myocardial β-adrenoreceptors and PKA downstream
targets, and is responsible for the observed positive inotropic effect of obestatin. An alternative explanation of our data
is that obestatin directly enhances the effect of myocardial β-adrenergic signaling. 相似文献
13.
《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1986,889(2):171-178
Human neutrophils can be permeabilized with the cholesterol complexing agent digitonin and then induced to secrete lysosomal constituents by increases in free Ca2+ alone. In order of increasing requirements for Ca2+, vitamin B-12 binding protein, lysozyme and β-glucuronidase were released. A variety of guanine nucleotides were examined with respect to their abilities to modulate this response. GTP, along with its analogues 5′-guanylylimidodiphosphate (Gpp[NH]p) and guanosine-5′-O-[3-thio]-triphosphate (GTP[γS]) decreased the Ca2+ requirements for secretion of all three granule constituents by one third to one order of magnitude. This synergy was dependent upon the concentration of guanine nucleotides employed. The effects of Gpp[NH]p could be blocked with the inactive derivative GDP[β-S]. The active guanine nucleotides, particularly GTP, served as stimuli in their own right. At high concentrations of Ca2+ and GTP, degranulation was strikingly inhibited; inhibition was also achieved with high concentrations of guanylyl[β,γ-methylene]diphosphate (Gpp[CH2]p). Both GDP and GMP were without any effect. When neutrophils were pretreated with pertussis toxin, granule discharge induced by fMet-Leu-Phe was almost completely blocked, as reported by others. If the neutrophils pretreated with pertussis toxin were then permeabilized with digitonin, the synergy between Ca2+ and the stimulatory guanine nucleotides was maintained. These data suggest the involvement of G-proteins in secretion induced by Ca2+; however, this response either uses a different G-protein or a different pool of G-proteins from those responses triggered by fMet-Leu-Phe. 相似文献
14.
Whole-cell patch-clamp techniques were used to measure anion currents through the plasma membrane of protoplasts of mesophyll
cells of expanding pea (Pisum sativum L.) leaves. Voltage-induced changes of the currents could be modelled with single exponential activation and deactivation
kinetics. The anion currents were activated at negative membrane potentials. The time constant of activation, τact, increased from 145 ms at −140 mV to 380 ms at −20 mV. A Boltzmann fit to the activation curve, n∞ (ΔGVm/ΔGmax), yielded a half-activation voltage of +27 mV. Opening and closing rate constants, α and β respectively, were calculated
from the values of τ and n∞. The currents depended on the presence of cytoplasmic Ca2+ concentrations higher than 10−6 M. Including 3 mM MgATP in the intracellular solution resulted in a voltage-dependent inactivation of the anion current.
The conductance-voltage relation resulting from the voltage-dependent activation and inactivation had a maximum at about −25
mV. The relations of the current in pea are discussed with respect to the anion currents in guard cells and suspension-cultured
tobacco cells, and its possible role in growing leaf cells.
Received: 1 March 1996 / Accepted: 16 September 1996 相似文献
15.
Pamela D. Arora Kathryn J. Bibby Christopher A. G. McCulloch 《Journal of cellular physiology》1994,161(2):187-200
Calcium transients in single, human gingival fibroblasts were studied after mechanical stretching of flexible culture substrates. A model system was developed to reproducibly stretch and rapidly (< 1 sec) refocus cells in the same focal plane so that changes in the concentration of free intracellular calcium ions ([Ca2+]i) were monitored without delay. Attached cells were grown on flexible bottom Petriperm dishes, loaded with fura-2/AM, and stretched by 1% or 2.8% of substrate area. The stretch caused no significant cell detachment or membrane lesions. A 1% stretch induced no calcium response, but a 2.8% stretch stimulated an initial calcium transient and the subsequent generation of [Ca2+]i oscillations of up to 2,000 sec. At 1% stretch, there was no calcium response. Cell shape and plating time were important determinants in the calcium response to mechanical stimulation: the responder cells were small and round without long processes. Major calcium transients were inhibited completely by 5 mM EGTA or by 10 μM gadolinium ions, by 50 μM nifedipine, or 250 μM verapamil, suggesting an influx of calcium through stretch-activated (SA) channels and L-type calcium channels. Depolarization by high KCl (144 mM) in the extracellular medium enhanced the amplitude of calcium transients by 54%. Calcium oscillations were not inhibited by preincubation with thapsigargin, caffeine, cholera toxin, staurosporine or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), indicating that IP3 sensitive pools, IP3 insensitive pools, G5α subunits, and protein kinase C, respectively, were not involved in the generation of calcium oscillations. Pretreatment with genistein, a specific tyrosine kinase inhibitor or cytochalasin D, an inhibitor of actin polymerization, or pertussis toxin, an inhibitor of Giα and Goα subunits, completely abolished calcium transients and oscillations. These results indicate that Ca2+ flux due to mechanical stretching is likely mediated through SA ion channe s and is dependent on tyrosine kinases, pertussis toxin-sensitive subunits of G-proteins, and actin filaments. © 1994 Wiley-Liss, Inc. 相似文献
16.
Heterotrimeric GTP-binding proteins (G-proteins), consisting of Gα, Gβ, and Gγ subunits, function as molecular switches in
many eukaryotic signal transduction pathways. In contrast to many eukaryotes, plants contain very few G-protein subunit isoforms
that mediate a diverse array of signalling functions. We investigated the contribution of cell type-specific expression and
subcellular localization to this multifunctional signalling capacity for the Arabidopsis thaliana Gβ subunit, AGB1. Analysis of AGB1 promoter::β-glucuronidase (GUS) fusions in germinating seeds, seedlings, and flowering plants revealed that AGB1 is widely expressed throughout development in a complex manner. As well as demonstrating similarities to existing Arabidopsis G-protein subunit expression data, several features of the AGB1 expression pattern align closely with known or proposed G-protein functions. A C-terminal AGB1-green fluorescent protein
(GFP) fusion was localized at the plasma membrane and in the nucleus of leaf epidermal cells, trichomes and root cells, supporting
previous evidence that plant G-protein functionality relies on subcellular compartmentalization. 相似文献
17.
To investigate whether cyclic GMP (cGMP) would mediate, in an intracellular Ca2+ -dependent manner, coupling of auxin to stomatal opening, the stomatal opening responses to the auxin indolyl-3-butyric acid
(IBA) and to the cGMP membrane-permeable derivative 8-bromoguanosine 3′,5′-cyclic monophosphate (8-Br-cGMP) were compared in epidermal strips of Commelina communis. In this comparison were studied possible effects of intracellular Ca2+ modulators, GTP-binding protein (G-protein) modulators and selective inhibitors of enzymatic reactions which use or generate
cGMP. The stomatal response to IBA was almost similarly reversed by the Ca2+ buffer 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), the intracellular Ca2+-release inhibitors ruthenium red and procaine, the inactive cGMP analog Rp-8-bromoguanosine 3′,5′-cyclic monophosphorothioate (Rp-8-Br-cGMPS), the inhibitor of cGMP-producing guanylyl cyclase LY 83583, the G-protein inhibitor
mas17 and the G-protein antagonist pGlu-Gln-D-Trp-Phe-D-Trp-D-Trp-Met-NH2. Comparison with stomatal opening in response to 8-Br-cGMP, which was almost completely suppressed by either BAPTA, ruthenium
red, procaine or Rp-8-Br-cGMPS, strongly suggests that cGMP acts downstream of G-protein activation as a second messenger
for IBA signal transduction and that the cGMP pathway likely depends on cytosolic Ca2+signaling.
Received: 8 November 1997 / Accepted: 6 March 1998 相似文献
18.
Ian Henry Lambert 《The Journal of membrane biology》1989,108(2):165-176
Summary The nature of the leukotriene-D4 (LTD4) induced cell shrinkage in Ehrlich ascites tumor cells has been investigated. LTD4 treatment of Ehrlich cells induces net loss of cellular KCl and cell shrinkage independent of the initial cell volume. LTD4 also produces water loss and reduction in cell volume when all extracellular and all intracellular Cl has been replaced by NO3. On the other hand, LTD4 fails to produce any significant changes in cell volume in the presence of the K-channel blocker quinine, suggesting that LTD4 in Ehrlich cells induces Cl-independent K loss through the Ca2+-dependent K channels. However, the effect of physiological doses of LTD4 on cell volume seems not to be as potent in Cl-free, NO3 cells when compared to Cl-containing cells, indicating that LTD4 in Ehrlich cells also provokes Cl-dependent K loss. LTD4 seems not to produce K loss through an electroneutral K+/H+ exchange system. LTD4 still produces Cl-independent K loss and cell shrinkage in the presence of the anticalmodulin drug pimozide but not in the presence of the LTD4 receptor antagonist L-649,923 or the 5-lipoxygenase inhibitor NDGA. Pretreatment of the cells with pertussis toxin, which inactivates inhibitory guanine nucleotide binding proteins (G-proteins), leads to partial inhibition of the LTD4-induced shrinkage. It is suggested that the LTD4-induced activation of K and Cl transporting systems in Ehrlich ascites tumor cells is mediated via a G-protein coupled receptor and that LTD4 might exert its effect through another lipoxygenase product. The Ca2+-calmodulin complex is not involved in the LTD4-induced activation of K and Cl transporting systems. 相似文献
19.
Adenosine Release and Uptake in Cerebellar Granule Neurons Both Occur via an Equilibrative Nucleoside Carrier that Is Modulated by G Proteins 总被引:6,自引:3,他引:3
M. I. Sweeney 《Journal of neurochemistry》1996,67(1):81-88
Abstract: There is debate about the mechanisms mediating adenosine release from neurons. In this study, the release of adenosine evoked by depolarizing cultured cerebellar granule neurons with 50 mM K+ was inhibited by 49 ± 7% in Ca2+-free medium. The remaining release was blocked by dipyridamole (IC50 = 6.4 × 10?8M) and nitrobenzylthioinosine (IC50 = 3.6 × 10?8M), inhibitors of adenosine uptake. Ca2+-dependent release was reduced by 78 ± 9% following a 21-h pretreatment of the cells with pertussis toxin, which ADP-ribosylates Gi/Go G proteins, thereby preventing their dissociation. The nucleoside transporter-mediated component of K+-induced adenosine release also was inhibited by 62 ± 8% by pertussis toxin and was potentiated by 78 ± 11% following cholera toxin treatment, which permanently activates Gs. Uptake of [3H]adenosine into cultured cerebellar granule neurons over a 10-min period was not dependent on extracellular Na+ but was reduced by dipyridamole (IC50 = 3.2 × 10?8M) and nitrobenzylthioinosine (IC50 = 2.6 × 10?8M). Thus, adenosine uptake likely occurs via the same transporter mediating Ca2+-independent adenosine release. Adenosine uptake was potentiated by cholera toxin pretreatment (152 ± 15% of control), but pertussis toxin had no statistically significant effect. It is possible that Gs, Gi/Go, or free Gβγ dimer modulate the equilibrative, inhibitor-sensitive nucleoside carrier to enhance adenosine transport. 相似文献
20.
Helena J. Bailes Robert J. Lucas 《Proceedings. Biological sciences / The Royal Society》2013,280(1759)
A subset of mammalian retinal ganglion cells expresses an opsin photopigment (melanopsin, Opn4) and is intrinsically photosensitive. The human retina contains melanopsin, but the literature lacks a direct investigation of its spectral sensitivity or G-protein selectivity. Here, we address this deficit by studying physiological responses driven by human melanopsin under heterologous expression in HEK293 cells. Luminescent reporters for common second messenger systems revealed that light induces a high amplitude increase in intracellular calcium and a modest reduction in cAMP in cells expressing human melanopsin, implying that this pigment is able to drive responses via both Gq and Gi/o class G-proteins. Melanopsins from mouse and amphioxus had a similar profile of G-protein coupling in HEK293 cells, but chicken Opn4m and Opn4x pigments exhibited some Gs activity in addition to a strong Gq/11 response. An action spectrum for the calcium response in cells expressing human melanopsin had the predicted form for an opsin : vitamin A1 pigment and peaked at 479 nm. The G-protein selectivity and spectral sensitivity of human melanopsin is similar to that previously described for rodents, supporting the utility of such laboratory animals for developing methods of manipulating this system using light or pharmacological agents. 相似文献