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PubMed1995

Chemoreceptor-mediated polymerization and depolymerization of actin in hair bundles of sea anemones.

Hair bundles located on tentacles of sea anemones are morphodynamic mechanoreceptors employed to regulate discharge of nematocysts into swimming prey. Activation of chemoreceptors for N-acetylated sugars is known to induce anemone hair bundles to elongate while shifting discharge to lower frequencies matching those produced by calmly swimming prey. In the continued presence of N-acetylated sugars, activation of proline receptors is known to induce hair bundles to shorten while shifting nematocyst discharge to higher frequencies presumed to correspond to movements produced by wounded, struggling prey. In the present study, N-acetylneuraminic acid (NANA) causes stereocilia to become more intensely fluorescent in confocal optical sections of phalloidin-stained specimens, suggesting that receptors for N-acetylated sugars initiate processes to increase the density of F-actin within stereocilia. Computer analysis of electron micrographs is consistent with this interpretation for large diameter stereocilia but not for small diameter stereocilia. In the continued presence of NANA, proline causes fluorescence intensity of phalloidin to decrease to or below control levels. DNaseI uniformly stains large diameter stereocilia, suggesting that these stereocilia contain a pool of G-actin. Fluorescence intensity of DNaseI in stereocilia is significantly less bright in specimens exposed to NANA alone than in specimens exposed to proline in the continued presence of NANA. It appears that whereas activated receptors for NANA induce G-actin to polymerize in large diameter stereocilia, activated receptors for proline induce F-actin to depolymerize, restoring G-actin pools.

Actins↗
PubMed2002

Carotid body chemoreceptors in dissociated cell culture.

Carotid body (CB) glomus or type 1 cells act as peripheral chemoreceptors which detect changes in arterial PO(2), PCO(2), and pH and help maintain homeostasis via the reflex control of ventilation. Over the last approximately 12 years significant progress has been made towards understanding chemotransduction mechanisms using freshly isolated or cultured type 1 cells. The latter preparation allows several powerful experimental manipulations (e.g., co-culture with sensory neurons) resulting in significant advances in our understanding of CB chemoreception. Here, we review several properties of type 1 cells after several days to weeks in culture. Typically, cultured type 1 cells grow in monolayer clusters enveloped by glial-like, type II, or sustentacular cells, which are immunopositive for the glial marker, glial fibrillary acid protein (GFAP). These cells can undergo DNA synthesis, evidenced by uptake of bromodeoxyuridine (BrdU), and show a limited capacity for cell division. Mitosis and survival of type 1 cells can be regulated by oxygen tension and/or growth factors (e.g., bFGF, insulin). In the rat, type 1 cells are immunopositive for several monoaminergic markers, including tyrosine hydroxylase (TH), dopamine transporter (DAT), and 5-HT. They also express cholinergic markers (e.g., vesicular acetylcholine transporter; VAChT), the highly conserved synaptic vesicle protein (SV2), and gap junctional proteins including Connexin 32 (Cx32). Moreover, in long-term culture ( approximately 2 weeks) they retain expression of O(2)-sensitive, TASK-1-like, and Ca(2+)-dependent (BK), K(+) channels as revealed by immunocytochemistry or RT-PCR analysis of mRNA extracted from type 1 clusters after removal from the culture surface.

Animals↗
PubMed1976

Ultrastructure of the blowfly chemoreceptor sensillum (Phormia regina).

The ultrastructure of a well studied insect chemosensory unit is presented in this report. Two separate lumina are present in this chemosensory unit, the trichogen and sensillar lumina. The fluid within the trichogen lumen exclusively bathes the dendritic terminals, and may be involved with the reception and/or modulation of environmental stimuli. Cytoplasmic extensions of the trichogen cell which line the trichogen lumen may be involved in the production of the cuticular sheath. The sensillar lumen is bordered by the tormogen and a sleeve cell, and is continuous with the unoccupied channel of the setal shaft. Functions for the various cellular components of the blowfly chemoreceptor sensillum are offered.

Animals↗
PubMed2001

NADPH oxidase does not account fully for O2-sensing in model airway chemoreceptor cells.

A key feature of O2 sensing by chemoreceptor tissues is the hypoxic inhibition of K+ channels. However, mechanisms coupling a fall of pO2 to channel closure differ between tissues: O2 regulation of K+ channels in chemoreceptive neuroepithelial bodies and their immortal counterparts, H146 cells, involves altered reactive oxygen species generation by NADPH oxidase. In contrast, this enzyme complex is not involved in O2 sensing by the carotid body and pulmonary vasculature. Here, we provide pharmacological evidence to support a role for NADPH oxidase in hypoxic inhibition of K+ currents in H146 cells. Two structurally unrelated NADPH oxidase inhibitors, diphenylene iodonium and phenylarsine oxide, suppressed hypoxic inhibition of K+ currents recorded using the patch-clamp technique. Most importantly, however, neither inhibitor fully blocked this response. Our findings provide the first evidence that multiple mechanisms may coexist within a specific cell type to account for hypoxic suppression of K+ channel activity.

Arsenicals↗
PubMed1995

Hypoxic ventilatory depression may be due to central chemoreceptor cell hyperpolarization.

By re-examining the results of various studies of HVD, of the localization of medullary CO2 chemosensory cells, and of their acid secretion, an hypothesis has been developed suggesting that the neurones which detect increased CO2 or CSF acid respond to decreased transmembrane H+ gradient, i.e. a greater fall in ECF than in ICF pH. Hypoxic lactic acid generated within these cells depresses activity, which can be restored by an appropriate rise of Paco2, disclosing both normal peripheral chemoreceptor hypoxic sensitivity and normal medullary integrative response.

Carbon Dioxide↗
PubMed1993

Multi-unit compartmentation of the carotid body chemoreceptor by perineurial cell sheaths: immunohistochemistry and freeze-fracture study.

The existence and extent of the perineurial cell envelope in the carotid body was clearly demonstrated by the immunoreactivity for nerve growth factor receptor (NGFR) and the freeze-fracture analysis. Consequently the chemoreceptor is regarded as multiple units, each of which consists of certain numbers of chief and sustentacular cells and nerves covered as a whole by a sheath of the perineurial cells.

Animals↗
PubMed1987

Ventilatory effects of adenosine mediated by carotid body chemoreceptors in the rat.

The effects of intracarotid injections of adenosine and adenosine analogues [5'-N-ethylcarboxamidoadenosine (NECA), 2-chloroadenosine (CADO), L-N6-phenylisopropyladenosine (L-PIA) and D-N6-phenylisopropyladenosine (D-PIA)] on ventilation were studied in rats anaesthetized with sodium pentobarbitone or urethane. Adenosine and its analogues increased in a dose-dependent manner respiratory ventilation determined as increases in tidal volume (VT), respiratory frequency (f) and minute volume (VE). These excitatory effects were abolished after section of the carotid sinus nerve. The order of potency of the adenosine analogues was NECA greater than CADO greater than D-PIA, L-PIA, and no marked stereoselectivity was found for the PIA isomers. The methylxanthine, theophylline, in a dose that did not modify respiratory ventilation, antagonized the excitatory action of CADO. An inhibitory, delayed and long-lasting effect of L-PIA on respiration was also observed after its intravenous administration, an effect which was not prevented by section of the carotid sinus nerves. It is concluded that adenosine can have both excitatory and inhibitory effects on ventilation, and that its excitatory effect mediated through carotid body chemoreceptors involves an A2 adenosine receptor.

2-Chloroadenosine↗
PubMed1976

Morphology and ultrastructure of the antennal chemoreceptors and mechanoreceptors of worker Coptotermes formosanus Shiraki.

Three types of setae were found on the antenna of workers of C. formosanus. Sensilla basiconica function as chemoreceptors. They are non-socketed, with fixed plate base, thin walled, and perforated. Pore tubules are contained within the cuticular pores of s. basiconica. The pore tubules have direct contact with the dendritic branches within the sensilla. The other sensilla are tactile mechanoreceptors. The longest setae (sensilla trichodea) are thick walled, socketed, mononeuronic, and non-perforated. The shorter mechanoreceptors (sensilla chaetica) have the same characteristics as s. trichodea, except that they are sometimes dineuronic. The numbers and distribution of the sensilla were established.

Animals↗
PubMed1981

The phosphoenolpyruvate-dependent carbohydrate: phosphotransferase system enzymes II as chemoreceptors in chemotaxis of Escherichia coli K 12.

In Escherichia coli K12, eight substrate-specific, membrane-bound enzymes II of the PEP-dependent carbohydrate: phosphotransferase system (PTS), specific for hexoses, hexosamines and hexitols, have been characterised in a series of isogenic and constitutive strains. In such mutants, lacking all but one enzyme II, the transport and vectorial phosphorylation activities as well as the chemotactical response in capillary tube assays have been compared. According to the data obtained, all enzymes II not only are directly involved in the transport and vectorial phosphorylation of their substrates, but they have also a primary role as the chemoreceptors for these substrates: (1) Metabolism of the attractant beyond the phosphorylation step is not a pre-requisite to eliciting positive chemotaxis. (2) Mutants, having only one enzyme II react in the capillary tube assay only to substrates of this enzyme II, but not to substrates of the missing enzymes II. This holds for enzymes II consisting of one membrane-bound protein as well as for systems containing a soluble factor III (FIII). (3) The substrate specificities or affinities, whether tested by transport and chemotaxis assays in vivo or by phosphorylation tests in vitro, are in correspondence. (4) The activities of enzymes II, regulated in a complex way at the level of enzyme synthesis and activity and tested as above, are also in agreement, (5) Mutants lacking the soluble proteins enzyme I or HPr of the PTS no longer respond chemotactically to any substrate taken up and phosphorylated by enzymes II. It is concluded that in PTS enzymes II some functions required for transport and chemotaxis are identical. It is suggested furthermore, that the alternation of intrinsic membrane-bound proteins between a phosphorylated and a dephosphorylated state, rather than binding of the substrate to the enzyme II, is the decisive stimulus in the chemotaxis toward carbohydrates taken up by these transport systems.

Bacterial Proteins↗
PubMed1987

Sequence of the mglB gene from Escherichia coli K12: comparison of wild-type and mutant galactose chemoreceptors.

The mglB gene of Escherichia coli codes for a galactose-binding protein (GBP) that serves both as the galactose chemoreceptor and as the recognition component of the beta-methylgalactoside transport system. The mglB551 mutation eliminates the chemotactic function of GBP without altering its transport or substrate-binding properties. To investigate the interaction between GBP and Trg, the chemotactic signal transducer for galactose, we sequenced the mglB genes from wild-type and mglB551 mutant strains. The mutation causes the replacement of Gly74 of GBP by Asp. This residue is located in alpha-Helix III at the tip of the P domain in the GBP tertiary structure farthest removed from the substrate-binding cleft between the P and Q domains. We conclude that Helix III must be part of, or at least adjacent to, the recognition site for Trg. Our sequence also included part of the mglA gene, which is immediately distal to mglB. The amino acid sequence deduced for the beginning of the MglA protein showed homology with a family of polypeptides that contain an ATP-binding site and are components of binding-protein-dependent transport systems.

Amino Acid Sequence↗
PubMed1982

Inhibition of the carotid chemoreceptor reflex by enflurane in chronically instrumented dogs.

The effect of the volatile inhalational anaesthetic enflurane (2 vol% and 4 vol%) on the cardiovascular response to carotid chemoreceptor stimulation (CCRS) was studied in 8 chronically instrumented dogs. Intracarotid injections of nicotine were used to evoke CCRS. Ventilation was held constant during the unanaesthetized state as well as the anaesthetized state. In the unanaesthetized state CCRS evoked an increase in iliac vascular resistance, and an increase in cardiac cycle length. Enflurane 2 vol% significantly attenuated the increases both in iliac vascular resistance as well as in cardiac cycle length. Enflurane 4 vol% abolished the response to CCRS.

Animals↗
PubMedDate not supplied

Impulse activity of medulla oblongata in rats in response to stimulation of taste receptors and visceral chemoreceptors.

We have recorded extracellularly the impulse activity of the rat medulla oblongata during stimulation of taste receptors of the tongue and visceral chemoreceptors with solutions of hydrochloric acid and sodium chloride. We have detected in the caudal region of the nucleus of the solitary tract, neurons that react to the chemical stimulation of either one or both the receptive zones mentioned. The response reactions of the isolated groups of units (taste, viscerochemical, and convergent neurons) are tonic and are characterized by a high level of impulse activity. We have established that the neurons of each of the groups isolated are capable of discriminating between salt and acid solutions. Using the example of sodium chloride solutions we have shown that an increase in the number of viscerochemical neurons which inhibit their own background activity on increase in the concentration of any substance in the intestine is an important index of the satiation of an animal and can serve as a starting link in the mechanism of food rejection.

Animals↗
PubMed1984

Estimating medullary chemoreceptor blood flow from ventilatory-CO2 response transients: theory and data from anesthetized dogs.

We examined the tracer wash-in technique for measuring blood flow for a specific experimental model in which medullary chemoreceptor blood flow is estimated using carbon dioxide as the tracer. Using a mathematical model, we calculated the flow values that would be estimated when blood flow is a function of the tracer concentration, CO2. The estimate was compared with three indices of time-varying blood flow: the steady-state blood flow before and after the step change of CO2 and the time-average blood flow. Estimated blood flow was found to be most closely related to the final value of flow. Perfusion estimates from five pentobarbital anesthetized dogs were 102 ml/100 g/min (S.D. 35) at an average of PaCO2 of 60.7 Torr.

Animals↗
PubMed1990

Three types of neurochemically defined autonomic fibres innervate the carotid baroreceptor and chemoreceptor regions in the guinea-pig.

The innervation of the carotid body, carotid sinus, and neighbouring arteries (common carotid artery; external carotid artery; occipital artery; ascending pharyngeal artery) was investigated in guinea-pigs by means of glyoxylic acid-induced catecholamine-fluorescence and immunohistochemistry using a variety of antisera against neuropeptides and tyrosine hydroxylase (TH). Fibres displaying catecholamine-fluorescence, TH- and neuropeptide Y-like immunoreactivity (NPY-LI) were less numerous in the carotid sinus than in all other arterial segments. Vasoactive intestinal polypeptide (VIP)-LI axons were almost lacking in the common carotid, external carotid and occipital arteries, consistently found in the carotid sinus, and more numerous in the ascending pharyngeal artery. Catecholaminergic, TH-, NPY- and VIP-LI fibres were observed deep in the media of the carotid sinus, where the baroreceptor terminals are located. In contrast, they did not enter the media in the adjacent arterial segments. All these fibres disappeared following excision of the superior cervical ganglion, but were unaffected by combined transection of the carotid sinus nerve and resection of the no-dose ganglion, suggesting a sympathetic origin. Double-staining immunofluorescence revealed at least three types of autonomic, presumably sympathetic fibres in the carotid sinus: 1) TH+/NPY+, 2) NPY+/VIP+, and 3) VIP+ fibres. This points to a non-noradrenergic efferent innervation of the carotid sinus in addition to the hitherto known noradrenergic sympathetic fibres. The three populations of autonomic fibres seen in the carotid sinus were also observed in the carotid body, but the paucity of NPY+/VIP+ double-labelled fibres raises doubt as to the functional significance of this particular fibre type in modulating arterial chemoreception. The multiplicity of neurochemically defined autonomic nerves to the carotid baro- and chemoreceptor regions probably reflects functionally separate pathways that are differently regulated and exert different effects.

Animals↗
PubMed2002

Effects of lung volume and chemoreceptor activity on blood pressure and R-R interval during the Valsalva maneuver.

STUDY OBJECTIVES: The purpose of the present investigation was to examine the effect of lung volume and inspiration of 100% oxygen on blood pressure and R-R interval responses during the Valsalva maneuver. DESIGN AND PARTICIPANTS: Fourteen healthy subjects completed eight Valsalva maneuvers. Four of the maneuvers were completed after inspiring to total lung capacity while the remaining maneuvers were completed at end-expiratory lung volume. Two maneuvers completed at a given lung volume were performed under hyperoxic conditions while the remaining maneuvers were completed under normoxic conditions. RESULTS: Overall, a significant increase in blood pressure and decrease in R-R interval occurred throughout phases I-IV of the Valsalva maneuvers that were initiated from end-expiratory lung volume as compared to total lung capacity. These changes were accompanied by a concomitant increase in baroreflex sensitivity during phase IV. Furthermore, independent of lung volume the baroreflex response was attenuated under hyperoxic conditions. CONCLUSIONS: We conclude that the lung volume that exists prior to the onset of the maneuver alters the blood pressure and R-R interval response during phases I-IV of the Valsalva maneuver. Furthermore, we suggest that these responses are mediated in part by changes in chemoreceptor activity since the baroreflex was reset and the sensitivity was reduced under hyperoxic conditions. Given these findings, we recommend that lung volume be controlled when patients are completing a Valsalva maneuver to obtain reliable and reproducible measures of blood pressure, R-R interval duration and baroreflex sensitivity.

Administration, Inhalation↗
PubMed1983

Does low pH stimulate central chemoreceptors located near the ventral medullary surface?

An in vitro preparation of the medulla oblongata of the rat was used to examine the responses to reducing pH, at constant CO2, of neurons in several identified nuclei. Neurons in an area close to the ventral surface, which is thought to be the location of pH-sensitive central respiratory chemoreceptors, did not respond differently from neurons in other medullary nuclei.

Acid-Base Equilibrium↗
PubMed1989

Effects of cyanide and uncouplers on chemoreceptor activity and ATP content of the cat carotid body.

In cat carotid bodies (c.b.'s) incubated in vitro with [3H]tyrosine to label the stores of catecholamines, it was found that CN promotes dose- and Ca2+-dependent release of [3H]dopamine (DA) from c.b. tissues in parallel to the increased electrical activity recorded from the carotid sinus nerve (c.s.n.). Two different uncouplers, dinitrophenol (DNP) and carbonyl-cyanide-m-chlorophenyl-hydrazone (CCCP), both activate also in a dose-dependent fashion, release of DA and electrical activity in the c.s.n. However, while cyanide (CN) (10(-4) M) applied during 5 min reduced the adenosine triphosphate (ATP) content of the c.b. by 45%, DNP (2.5 x 10(-4) M) and CCCP (10(-6) M) applied for the same period of time did not modify the ATP levels of the organ. At the above concentrations, the 3 agents increased about 8-fold the electrical activity recorded from the c.s.n. Thus, contrary to the postulates of the metabolic hypotheses, our findings indicate that the decrease in the ATP content in the c.b. is not a prerequisite for the activation of the chemoreceptors. We propose alternative mechanisms to explain the chemostimulant action of the metabolic poisons.

Action Potentials↗
PubMed1989

ATP-sensitive chemoreceptors: antagonism by other nucleotides and the potential implications of ectonucleotidase activity.

As measured by extracellular single-cell recording, the responses to adenosine triphosphate (ATP) by ATP-sensitive chemoreceptors (ATP cells) on the olfactory organ of the spiny lobster are markedly suppressed by adenosine diphosphate (ADP), adenosine monophosphate (AMP) and to a lesser extent, adenosine, when each is presented in binary mixture with ATP. In the presence of ADP, the dose-response function for ATP exhibits an apparent parallel displacement to the right suggesting that this antagonism may occur via competition at the ATP receptor. Structure-activity relationships reveal that the structural requirements for antagonism by diphosphate analogs of ADP bear little relationship to the requirements for the agonistic activity of corresponding triphosphate analogs. Under Mg2+-free conditions, the desensitization of ATP cells tends to be delayed resulting in enhanced responses to ATP. Desensitization does not appear to be related to the generation of the antagonist, ADP, from ATP via ecto-ATPase activity. The results of this study suggest that the responses of ATP cells to the ATP contained in natural stimulus (odor) mixtures can be tempered by the suppressive interactions of other nucleotides in the mixtures. Furthermore, these interactions may be mitigated and/or intensified by the actions of sensillar ectonucleotidases.

5'-Nucleotidase↗