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At least 991 records · Page 55Linked to original sources
PubMed1966

The effects of hypoxia in the new-born lamb before and after denervation of the carotid chemoreceptors.

1. Twenty-seven unanaesthetized new-born lambs, 6 hr-10 days old, responded to two levels of inspired oxygen, 125 and 110 mm Hg (alveolar CO(2) being controlled) with a sustained increase in minute ventilation (V), a small increase in heart rate and a less consistent rise in systemic blood pressure.2. An increase in V was observed when arterial oxygen tension (P(a), (O2)) had fallen by 6-15 mm Hg. There appeared to be no fixed threshold of P(a), (O2) at which ventilation started to increase.3. The increase in ventilation caused by these levels of hypoxia was significantly and directly related to the age of the lamb and to its control alveolar CO(2).4. More severe hypoxia caused a progressive increase in V until P(a), (O2) was about 25 mm Hg when respiration failed. This increase at P(a), (O2) > 25 mm Hg was markedly potentiated when alveolar P(CO2) (P(A), (CO2)) was increased and abolished after bilateral denervation of the carotid chemoreceptors.5. Significant (> 10%) left-to-right shunts were found in ten out of twelve lambs lightly anaesthetized with pentobarbitone sodium, breathing air. Hypoxia diminished the left-to-right pressure gradient largely by its pressor effect on the pulmonary circulation. When inspired O(2) tension (P(I), (O2)) was 70 mm Hg, all seven lambs studied showed a reversal of the pressure gradient and evidence of right-to-left shunts (11-42%) across the ductus arteriosus.6. The implications of these findings have been discussed with reference to previous studies of the new-born response to hypoxia and it is concluded that the peripheral chemoreceptors are fully active at birth and in the new-born period.

Animals↗
PubMed1971

On the direct and crossed components of reflex responses to unilateral stimulation of the carotid body chemoreceptors in the dog.

1. In dogs under chloralose-urethane anaesthesia the chemoreceptors of the two carotid bodies were separately stimulated.2. The distribution of three primary reflex responses to carotid body stimulation was studied: parasympathetic bradycardia, sympathetic vasoconstriction, and increase in somatic phrenic nerve activity.3. The reflex bradycardia evoked by either carotid body was mediated by both vagus nerves, but when either vagus was blocked a greater response could be obtained from the contralateral than from the ipsilateral carotid body.4. The reflex vasoconstriction evoked by either carotid body was seen in both hind limbs, with no predominance in either limb.5. The reflex increase in phrenic nerve activity evoked by either carotid body was seen in both phrenic nerves, with no predominance in either nerve.

Anesthesia, General↗
PubMed1977

Hyperpolarizing effects of dopamine on chemoreceptor nerve endings from cat and rabbit carotid bodies in vitro.

1. The effects of dopamine on DC potential changes recorded from the carotid sinus nerve were studied in vitro using carotid bodies and associated sinus nerves removed from anaesthetized cats and rabbits.2. The carotid body was placed in one compartment of a superfusion chamber and was superfused with buffered salt solution. The carotid sinus nerve was led into an adjoining compartment, containing lightweight mineral oil, for recording DC potential changes with chlorided silver electrodes.3. Dopamine injected into the superfusing solution in amounts of 50-250 mug caused hyperpolarization of the DC potential. This effect occurred repeatedly in each preparation, the maximum number of tests in any one preparation being twenty-seven.4. In the same preparations, acetylcholine (50-100 mug) and NaCN (10-20 mug) caused depolarizations of the DC potential, effects that have been described by others.5. The hyperpolarizing effects of dopamine were reduced or abolished by the alpha-adrenergic antagonists, dihydroergotamine (10-100 mug/ml.) and phenoxybenzamine (5 mug/ml.) and the dopamine antagonist droperidol (10-25 mug/ml.).6. The results indicate that the inhibitory effects of dopamine on the frequency of carotid body chemosensory discharges in cats and rabbits are due to hyperpolarization of chemoreceptor afferent nerve endings and not necessarily to local vascular effects in the carotid body.

Adrenergic alpha-Antagonists↗
PubMed1977

Synaptic excitation and inhibition resulting from direct action of acetylcholine on two types of chemoreceptors on individual amphibian parasympathetic neurones.

1. Synaptic transmission was studied in visually identified parasympathetic ganglion cells that modulate the heart beat of the mudpuppy Necturus maculosus).2. The brief pulse of acetylcholine (ACh) released from terminals of the vagus nerve after each impulse can produce two distinct post-synaptic responses in individual principal cells of the ganglion: (i) within a milli-second of release, ACh generates a rapid and strong excitatory post-synaptic potential (e.p.s.p.) that normally initiates a post-synaptic impulse; (ii) this excitation is usually followed by a slow hyperpolarizing inhibitory post-synaptic potential (i.p.s.p.) that lasts for several seconds. The magnitude and time course of the i.p.s.p. depends on the frequency and number of vagal stimuli. When the hydrolysis of ACh is inhibited by prostigmine, a train of nerve stimuli may be followed by an i.p.s.p. lasting half a minute or longer.3. The rapid e.p.s.p. and slow i.p.s.p. result from the direct action of ACh on two different types of chemoreceptors in the post-synaptic membrane of the principal cell. The e.p.s.p. can be preferentially blocked by the nicotinic antagonist dihydro-beta-erythroidine (5 x 10(-7)M), while the i.p.s.p. is selectively blocked by the muscarinic antagonist atropine (5 x 10(-9)M).4. Potentials resembling nerve-evoked e.p.s.p.s and i.p.s.p.s can be produced by iontophoretic release of ACh from micropipettes onto the post-synaptic membrane. Application of the muscarinic agonist bethanechol generates exclusively inhibitory responses.5. The reversal potential for the i.p.s.p. is about -105 mV, which is approximately the equilibrium potential for potassium (E(K)). When the external K(+) concentration is altered, the reversal potential for inhibition is shifted to the new value of E(K) as expected from the Nernst equation. Changes in the external Na(+) and Cl(-) concentrations have no appreciable effect on the reversal potential. Thus, the i.p.s.p. is the result of a conductance increase for K(+).6. The conductance change producing the i.p.s.p. is voltage sensitive. When the membrane potential is shifted from -40 to -60 mV, the i.p.s.p becomes larger and longer. Beyond -60 mV the inhibitory response decreases in proportion to the driving force on K(+) without any further change in time course.7. The inhibitory response produced by an iontophoretically applied pulse of bethanechol has a delayed onset of about 150 msec at 24 degrees C. The early portion of this response, including the delay, is proportional to t(3), where t is time. The proportionality factor (the apparent rate constant) decreases elevenfold when the temperature is lowered by 10 degrees C. This suggests that a multi-step process is involved in the activation of the conductance increase that leads to the inhibitory response. Inhibitory responses with similar kinetics were produced in heart muscles of the mudpuppy upon application of ACh.

Acetylcholine↗
PubMed1992

Effects of left atrial receptor stimulation on carotid chemoreceptor-induced renal responses in dogs.

1. Dogs were anaesthetized with thiopentone sodium and alpha-chloralose and artificially ventilated. The carotid sinus regions were vascularly isolated and perfused with arterial or venous blood to stimulate the chemoreceptors. Left atrial receptors were stimulated by distending four balloons, three in the left pulmonary vein-atrial junctions and one in the left atrial appendage. Mean aortic pressure was held constant by means of a pressure control device. Atenolol and atropine (2.0 and 0.5 mg kg-1, respectively), and gallamine triethiodide (3.0 mg kg-1 h-1) were given I.V. Renal blood flow was measured by an electromagnetic flowmeter, glomerular filtration rate by creatinine clearance, urinary sodium by flame photometry and solute excretion by osmometry. 2. In fifteen tests in eight dogs (in one dog responses of both left and right kidneys were determined), at a constant aortic pressure (AoP) of 92.0 +/- 3.2 mmHg, and carotid sinus pressure (CSP) of 95.0 +/- 2.0 mmHg, stimulation of left atrial receptors with balloon inflation resulted in significant increases in renal blood flow (RBF) by 8.3 +/- 0.9 from 255.0 +/- 14.6 ml min-1 (100 g kidney weight)-1 (n = 9), in glomerular filtration rate (GFR) by 4.1 +/- 0.6 from 21.2 +/- 1.9 ml min-1 (100 g)-1, in filtration fraction (FF) by 0.04 +/- 0.003 from 0.20 +/- 0.01, in urine flow rate (V) by 0.08 +/- 0.02 from 0.33 +/- 0.05 ml min-1 (100 g)-1, in sodium excretion (UNaV) by 4.4 +/- 0.9 from 27.7 +/- 4.2 mumol min-1 (100 g)-1, in osmolar excretion (UosmV) by 62.0 +/- 5.6 from 303.0 +/- 28.3 mu osmol min-1 (100 g)-1, and in a decrease in free water clearance (CH2O) by 0.13 +/- 0.03 from -0.63 +/- 0.04 ml min-1 (100 g)-1. Left atrial pressure (LAP) and heart rate (HR) did not change significantly from 6.9 +/- 0.3 cmH2O, and 133.0 +/- 3.4 beats min-1 respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

L- and N-type Ca2+ channels in adult rat carotid body chemoreceptor type I cells.

1. Whole-cell voltage-dependent Ca2+ currents recorded from chemoreceptor type I cells of the adult rat carotid body had maximum amplitudes of -94 pA in 10 mM Ca2+ and were half-inactivated at a holding potential of -38 mV. Somatostatin and dopamine inhibited whole-cell Ca2+ current in type I cells. 2. The dihydropyridine agonist (+)202-791 increased the Ca2+ current amplitude by 106% at a step potential of -18 mV. The dihydropyridine antagonist nimodipine decreased the Ca2+ current amplitude by 40% from a holding potential of -80 mV, and by 74% from a holding potential of -60 mV. The nimodipine-sensitive current had a maximum amplitude at a membrane potential of -12 mV. omega-Conotoxin GVIA (omega-CgTX GVIA) blocked the whole-cell Ca2+ current by 40%. The omega-CgTX GVIA-sensitive current had a maximum amplitude at a membrane potential of +2 mV. 3. In summary, type I cells of the adult rat carotid body have dihydropyridine-sensitive L-type and omega-conotoxin GVIA-sensitive N-type voltage-dependent Ca2+ channels. These channels may play a role in the voltage-gated entry of Ca2+ necessary for stimulus-secretion coupling in response to changes in arterial PO2, PCO2 and pH. Inhibition of the Ca2+ currents by somatostatin and dopamine may alter the chemotransduction signal in type I cells.

Animals↗
PubMed2005

An interneuronal chemoreceptor required for olfactory imprinting in C. elegans.

Animals alter their behavioral patterns in an experience-dependent manner. Olfactory imprinting is a process in which the exposure of animals to olfactory cues during specific and restricted time windows leaves a permanent memory ("olfactory imprint") that shapes the animal's behavior upon encountering the olfactory cues at later times. We found that Caenorhabditis elegans displays olfactory imprinting behavior that is mediated by a single pair of interneurons. To function in olfactory imprinting, this interneuron pair must express a G protein-coupled chemoreceptor family member encoded by the sra-11 gene. Our study provides insights into the cellular and molecular basis of olfactory imprinting and reveals a function for a chemosensory receptor family member in interneurons.

Animals↗
PubMed1988

Sugar and signal-transducer binding sites of the Escherichia coli galactose chemoreceptor protein.

D-galactose-binding (or chemoreceptor) protein of Escherichia coli serves as an initial component for both chemotaxis towards galactose and glucose and high-affinity active transport of the two sugars. Well-refined x-ray structures of the liganded forms of the wild-type and a mutant protein isolated from a strain defective in chemotaxis but fully competent in transport have provided a molecular view of the sugar-binding site and of a site for interacting with the Trg transmembrane signal transducer. The geometry of the sugar-binding site, located in the cleft between the two lobes of the bilobate protein, is novel in that it is designed for tight binding and sequestering of either the alpha or beta anomer of the D-stereoisomer of the 4-epimers galactose and glucose. Binding specificity and affinity are conferred primarily by polar planar side-chain residues that form intricate networks of cooperative and bidentate hydrogen bonds with the sugar substrates, and secondarily by aromatic residues that sandwich the pyranose ring. Each of the pairs of anomeric hydroxyls and epimeric hydroxyls is recognized by a distinct Asp residue. The site for interaction with the transducer is about 18 A from the sugar-binding site. Mutation of Gly74 to Asp at this site, concomitant with considerable changes in the local ordered water structures, contributes to the lack of productive interaction with the transmembrane signal transducer.

Bacterial Proteins↗
PubMed2002

Two predicted chemoreceptors of Helicobacter pylori promote stomach infection.

Helicobacter pylori must be motile or display chemotaxis to be able to fully infect mammals, but it is not known how this chemotaxis is directed. We disrupted two genes encoding predicted chemoreceptors, tlpA and tlpC. H. pylori mutants lacking either of these genes are fully motile and chemotactic in vitro and are as able as the wild type to infect mice when they are the sole infecting strains. In contrast, when mice are coinfected with the H. pylori SS1 tlpA or tlpC mutant and the wild type, we find more wild type than mutant after 2 weeks of colonization. Neither strain has an in vitro growth defect. These results suggest that the tlpA- and tlpC-encoded proteins assist colonization of the stomach environment.

Animals↗
PubMed2006

Uropathogenic Escherichia coli strains generally lack functional Trg and Tap chemoreceptors found in the majority of E. coli strains strictly residing in the gut.

The prevalence and function of four chemoreceptors, Tsr, Tar, Trg, and Tap, were determined for a collection of uropathogenic, fecal-commensal, and diarrheagenic Escherichia coli strains. tar and tsr were present or functional in nearly all isolates. However, trg and tap were significantly less prevalent or functional among the uropathogenic E. coli strains (both in 6% of strains) than among fecal-commensal strains (both in > or =50% of strains) or diarrheal strains (both in > or =75% of strains) (P < 0.02).

Amino Acids↗
PubMed2006

Similarities and differences in interactions of the activity-enhancing chemoreceptor pentapeptide with the two enzymes of adaptational modification.

Sensory adaptation and chemotaxis by Escherichia coli require a specific pentapeptide at the chemoreceptor carboxyl terminus. This sequence binds the two enzymes of receptor adaptational modification, enhancing catalysis, but with different binding features and mechanisms. We investigated the relative importance of each pentapeptide side chain for the two enhancing interactions.

Binding Sites↗
PubMed2006

Functional analysis of nine putative chemoreceptor proteins in Sinorhizobium meliloti.

The genome of the symbiotic soil bacterium Sinorhizobium meliloti contains eight genes coding for methyl-accepting chemotaxis proteins (MCPs) McpS to McpZ and one gene coding for a transducer-like protein, IcpA. Seven of the MCPs are localized in the cytoplasmic membrane via two membrane-spanning regions, whereas McpY and IcpA lack such hydrophobic regions. The periplasmic regions of McpU, McpV, and McpX contain the small-ligand-binding domain Cache. In addition, McpU possesses the ligand-binding domain TarH. By probing gene expression with lacZ fusions, we have identified mcpU and mcpX as being highly expressed. Deletion of any one of the receptor genes caused impairments in the chemotactic response toward most organic acids, amino acids, and sugars in a swarm plate assay. The data imply that chemoreceptor proteins in S. meliloti can sense more than one class of carbon source and suggest that many or all receptors work as an ensemble. Tactic responses were virtually eliminated for a strain lacking all nine receptor genes. Capillary assays revealed three important sensors for the strong attractant proline: McpU, McpX, and McpY. Receptor deletions variously affected free-swimming speed and attractant-induced chemokinesis. Noticeably, cells lacking mcpU were swimming 9% slower than the wild-type control. We infer that McpU inhibits the kinase activity of CheA in the absence of an attractant. Cells lacking one of the two soluble receptors were impaired in chemokinetic proficiency by more than 50%. We propose that the internal sensors, IcpA and the PAS domain containing McpY, monitor the metabolic state of S. meliloti.

Amino Acids↗
PubMed1975

Role of the receptor for bacteriophage lambda in the functioning of the maltose chemoreceptor of Escherichia coli.

Chemotaxis towards maltose is specifically defective in many strains of Escherichia coli carrying mutations affecting lamB, the gene coding for the outer membrane receptor for bacteriophage lambda. However, with one exception, the most extreme effect of lamB mutants on the maltose response as determined in the capillary assay is a shift to higher sugar concentrations and a reduction in the number of bacteria accumulated to about 25% of the wild-type level. The severity of the taxis defect is strongly correlated with reduced ability of the cells to take up the maltose present at 1 and 10 muM. Evidence presented here and in the accompanying paper indicates that the lambda receptor is involved in the transport of maltose at these concentrations. The effects of lamB mutations on maltose taxis can be explained by postulating that the high-affinity maltose transport system in which the lambda receptor participates transfers maltose from the surrounding medium across the outer membrane and into the periplasmic space. If the maltose chemoreceptor detects sugar present in the periplasmic space, and not molecules external to the outer membrane, then defective transport of low concentrations of maltose into the periplasm would result in the observed apparent reduction in the sensitivity of the maltose receptor. Thus, the lambda receptor protein would participate in maltose chemorecepton only indirectly through its role in maltose transport.

Binding Sites↗
PubMed1991

Genetic evidence for interaction between the CheW and Tsr proteins during chemoreceptor signaling by Escherichia coli.

This study presents two lines of genetic evidence consistent with the premise that CheW, a cytoplasmic component of the chemotactic signaling system of Escherichia coli, interacts directly with Tsr, the membrane-bound serine chemoreceptor. (i) We demonstrated phenotypic suppression between 10 missense mutant CheW proteins and six missense mutant Tsr proteins. Most of these mutant proteins had leaky chemotaxis defects and were partially dominant, implying relatively minor functional alterations. Their suppression pattern was allele specific, suggesting that the mutant proteins have compensatory conformational changes at sites of interactive contact. (ii) We isolated five partially dominant CheW mutations and found that four of them were similar or identical to the suppressible CheW mutant proteins. This implies that there are only a few ways in which CheW function can be altered to produce dominant defects and that dominance is mediated through interactions of CheW with Tsr. The amino acid replacements in these mutant proteins were inferred from their DNA sequence changes. The CheW mutations were located in five regularly spaced clusters in the first two-thirds of the protein. The Tsr mutations were located in a highly conserved region in the middle of the cytoplasmic signaling domain. The hydrophobic moments, overall hydrophobicities, and predicted secondary structures of the mutant segments were consistent with the possibility that they are located at the surface of the CheW and Tsr molecules and represent the contact sites between these two proteins.

Amino Acid Sequence↗
PubMed1994

Constitutively signaling fragments of Tsr, the Escherichia coli serine chemoreceptor.

Tsr, the serine chemoreceptor of Escherichia coli, has two signaling modes. One augments clockwise (CW) flagellar rotation, and the other augments counterclockwise (CCW) rotation. To identify the portion of the Tsr molecule responsible for these activities, we isolated soluble fragments of the Tsr cytoplasmic domain that could alter the flagellar rotation patterns of unstimulated wild-type cells. Residues 290 to 470 from wild-type Tsr generated a CW signal, whereas the same fragment with a single amino acid replacement (alanine 413 to valine) produced a CCW signal. The soluble components of the chemotaxis phosphorelay system needed for expression of these Tsr fragment signals were identified by epistasis analysis. Like full-length receptors, the fragments appeared to generate signals through interactions with the CheA autokinase and the CheW coupling factor. CheA was required for both signaling activities, whereas CheW was needed only for CW signaling. Purified Tsr fragments were also examined for effects on CheA autophosphorylation activity in vitro. Consistent with the in vivo findings, the CW fragment stimulated CheA, whereas the CCW fragment inhibited CheA. CheW was required for stimulation but not for inhibition. These findings demonstrate that a 180-residue segment of the Tsr cytoplasmic domain can produce two active signals. The CCW signal involves a direct contact between the receptor and the CheA kinase, whereas the CW signal requires participation of CheW as well. The correlation between the in vitro effects of Tsr signaling fragments on CheA activity and their in vivo behavioral effects lends convincing support to the phosphorelay model of chemotactic signaling.

Bacterial Proteins↗
PubMed1996

Mutational analysis of a transmembrane segment in a bacterial chemoreceptor.

Trg is a member of a family of receptors that mediates chemotaxis by Escherichia coli. Its transmembrane domain is a loose four-helix bundle consisting of two helices from each of the two identical subunits. This domain mediates transmembrane signaling through a conformational change in which the second transmembrane segment (TM2) is thought to move relative to TM1, but mutational analysis of TM2 by cysteine scanning had identified only a few positions at which substitutions perturbed function or induced signaling. Thus, we performed mutational analysis by random mutagenesis and screening. Among 42 single-residue substitutions in TM2 that detectably altered function, 16 had drastic effects on receptor activity. These substitutions defined a helical face of TM2. This functionally important surface was directed into the protein interior of the transmembrane domain, where TM2 faces the helices or the other subunit. The functionally perturbing substitutions did not appear to cause general disruption of receptor structure but rather had more specific effects, altering aspects of transmembrane signaling. An in vivo assay of signaling identified some substitutions that reduced and others that induced signaling. These two classes were distributed along adjacent helical faces in a pattern that strongly supports the notion that conformational signaling involves movement between TM2 and TM1 and that signaling is optimal when stable interactions are maintained across the interface between the homologous helices in the transmembrane domain. Our mutational analysis also revealed a striking tolerance of the chemoreceptor for substitutions, including charged residues, usually considered to be disruptive of transmembrane segments.

Amino Acid Sequence↗
PubMed2001

Proteolysis of the Caulobacter McpA chemoreceptor is cell cycle regulated by a ClpX-dependent pathway.

Proteolysis is involved in cell differentiation and the progression through the cell cycle in Caulobacter crescentus. We have constitutively expressed the transmembrane chemoreceptor McpA from a multicopy plasmid to demonstrate that McpA degradation is modulated during the cell cycle. The level of McpA protein starts to decrease only when the swarmer cells differentiate into stalked cells. The reduction in McpA protein levels is maintained until the stalked cells develop into predivisional cells, at which point the level returns to that observed in swarmer cells. The cell-cycle-regulated degradation of McpA does not require the last 12 C-terminal amino acids, but it does require three amino acids (AAL) located 15 residues away from the C terminus. The ClpXP protease is essential in C. crescentus for viability, and thus, we tested McpA degradation in xylose conditional mutants. The effect on McpA degradation occurred within two generations from the start of ClpX depletion. The conditional mutants' growth rate was only slightly affected, suggesting that ClpX is directly involved in McpA proteolysis.

ATPases Associated with Diverse Cellular Activitie↗
PubMed2001

Substitutions in the periplasmic domain of low-abundance chemoreceptor trg that induce or reduce transmembrane signaling: kinase activation and context effects.

We extended characterization of mutational substitutions in the ligand-binding region of Trg, a low-abundance chemoreceptor of Escherichia coli. Previous investigations using patterns of adaptational methylation in vivo led to the suggestion that one class of substitutions made the receptor insensitive, reducing ligand-induced signaling, and another mimicked ligand occupancy, inducing signaling in the absence of ligand. We tested these deductions with in vitro assays of kinase activation and found that insensitive receptors activated the kinase as effectively as wild-type receptors and that induced-signaling receptors exhibited the low level of kinase activation characteristic of occupied receptors. Differential activation by the two mutant classes was not dependent on high-abundance receptors. Cellular context can affect the function of low-abundance receptors. Assays of chemotactic response and adaptational modification in vivo showed that increasing cellular dosage of mutant forms of Trg to a high-abundance level did not significantly alter phenotypes, nor did the presence of high-abundance receptors significantly correct phenotypic defects of reduced-signaling receptors. In contrast, defects of induced-signaling receptors were suppressed by the presence of high-abundance receptors. Grafting the interaction site for the adaptational-modification enzymes to the carboxyl terminus of induced-signaling receptors resulted in a similar suppression of phenotypic defects of induced-signaling receptors, implying that high-abundance receptors could suppress defects in induced-signaling receptors by providing their natural enzyme interaction sites in trans in clusters of suppressing and suppressed receptors. As in the case of cluster-related functional assistance provided by high-abundance receptors for wild-type low-abundance receptors, suppression by high-abundance receptors of phenotypic defects in induced-signaling forms of Trg involved assistance in adaptation, not signaling.

Amino Acid Sequence↗