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At least 1,171 records · Page 65Linked to original sources
PubMed1994

Electrophysiological responses of Xenopus oocytes to amino acids: criteria for expression of injected mRNA coding chemoreceptors.

Responses of endogenous transporters/receptors of Xenopus oocytes to L-alanine, L-arginine, L-leucine and L-serine were investigated under voltage clamp conditions. (a) Concentration-response relations for the amino acids followed Langmuir's adsorption isotherm. (b) The neutral amino acids required Na+ to elicit the responses, whereas L-arginine did not. (c) The responses to L-alanine decreased with decreasing pH and became undetectable at pH 5.5. The present experiments supply criteria to judge if the oocytes translate exogenous mRNA coding taste or olfactory receptor proteins for the amino acids, the best characterized stimuli, especially in fishes.

Amino Acids↗
PubMed1983

Narrow-spectrum chemoreceptor cells in the antennules of the American lobster, Homarus americanus.

The present study shows that smell (antennular) receptor cells are as narrowly tuned to single compounds as taste (leg) receptor cells in the lobster. Antennular receptors responded best to hydroxy-L-proline (57% of the 30 cells sampled) and taurine (24%). In the presence of 14 other compounds in equimolar concentrations, the hydroxy-L-proline and taurine receptors showed a suppressed response to their best stimulus. Other cells had best responses to ammonium chloride, betaine, L-glutamate or L-proline. The results have implications for molecular receptor processes and for the neural basis of feeding behavior.

Action Potentials↗
PubMed1982

Chemoreceptors for serotonin (5-HT), acetylcholine (ACh), bradykinin (BK), histamine (H) and gamma-aminobutyric acid (GABA) on rabbit visceral afferent neurons.

The somata of type 'C' neurons in rabbit nodose ganglion are endowed with receptor sites for 5-HT, BK, ACh, II and GABA. 5-HT and ACh application to type 'C' neurons in the nodose ganglion of rabbits produced a rapid depolarization associated with an increased membrane conductance, most likely to Na+ and K+. BK and H elicited slow depolarizations accompanied by a decreased membrane conductance probably to K+. GABA induced a rapid depolarization associated with an increased conductance to Cl-. In contrast, type 'A' neurons were insensitive to the four algesic agents but responded to GABA. d-Tubocurarine or picrotoxin at relatively low concentrations blocked ACh, 5-HT and GABA depolarizations without affecting membrane properties. Hexamethonium blocked ACh responses but not 5-HT responses. In addition, no desensitization occurred between the substances 5-HT, ACh or BK. The results suggest that the depolarizing effect of these agents on visceral neurons might be exerted via different receptors.

Acetylcholine↗
PubMed1996

Characterisation of the mcpA and mcpB genes capable of encoding methyl-accepting type chemoreceptors in Rhodobacter capsulatus.

Two contiguous mcp genes, mcpA and mcpB, transcribed from the same DNA strand and capable of encoding methyl-accepting chemotaxis proteins (Mcp) have been isolated from Rhodobacter capsulatus (Rc), sequences and overexpressed in Escherichia coli (Ec). The deduced proteins (McpA, 69 171 Da; McpB, 81 629 Da) show a structure similar to that of Ec Mcp. The products of mcpA and mcpB, overproduced in Ec, were recognized by anti-Ec Mcp (Trg) antibodies.

Amino Acid Sequence↗
PubMed2006

Carotid chemoreceptor reflex modulation by arginine-vasopressin microinjected into the nucleus tractus solitarius in rats.

BACKGROUND: In addition to their role of sensing O2, pH, CO2, osmolarity and temperature, carotid body receptors (CBR) were proposed by us and others to have a glucose-sensing role in the blood entering the brain, integrating information about blood glucose and O2 levels essential for central nervous system (CNS) metabolism. The nucleus tractus solitarius (NTS) is an important relay station in central metabolic control and receives signals from peripheral glucose-sensitive hepatoportal afferences, from central glucose-responsive neurons in the brainstem and from CBR and arginine-vasopressin (AVP)-containing axons from hypothalamic nuclei. METHODS: In normal Wistar rats anesthetized with pentobarbital, permanent cannulas were placed stereotaxically in the NTS. Glucose changes were induced in vivo after CBR stimulation with sodium cyanide (NaCN-5 microg/100 g), preceded by an infusion of AVP [(10 or 40 pmol/100 nL of artificial cerebrospinal fluid) aCSF] or an antagonist for V1a receptors (anti-glycogenolytic vasopressin analogue-VP1-A) (100 pmol/100 nL of aCSF) into the NTS. RESULTS: CBR stimulation after an AVP infusion (larger dose) into the NTS resulted in a significantly higher arterial glucose and lower brain arterial-venous glucose difference. In the same way, VP1-A administration in the NTS significantly decreased the effects observed after AVP priming before CBR stimulation or preceding the CBR stimulation, alone. CONCLUSIONS: We propose that AVP in the NTS could participate in glucose homeostasis, modulating the information arising in CBR after histotoxic-anoxia stimulation.

Animals↗
PubMedDate not supplied

Stochastic pulse stimulation in chemoreceptors and its properties.

Orientation towards food and mate, especially in insects, is an olfactory-controlled behavior which relies on the detection of small amounts of odorant molecules delivered in turbulent atmospheric conditions, so that randomness in magnitude and time is a major feature of the natural stimulus. The effect of random delivery on the initial step of olfactory transduction, the formation of the receptor-ligand complex, is analyzed in the case of the moth pheromonal system. Two types of randomness are compared, Gaussian (regular) and exponential (irregular). The influence of noise is quantified either with the maxima of the receptor-ligand complex, or with the times at which the concentration of complex crosses a given threshold level. It is shown that the stochastic features of the stimulus helps its detection and that the exponential distribution appears not only as a better description of the natural stimulus, but also as the most efficient from a biological point of view.

Animals↗
PubMed2004

Arterial chemoreceptors in the superior laryngeal nerve of the rat.

Paraganglia resembling the carotid body have been described in the superior laryngeal nerve (SLN) of the rat and the aim of the present study was to determine if this tissue is chemosensitive. We developed a novel isolated SLN preparation superfused with HEPES-buffered Tyrode solution at 35 degrees C in vitro. A glass suction microelectrode was used to record the electrical activity of single SLN units and a micropipette was used to pressure-eject small volumes of sodium cyanide (NaCN; 250-500 ng in 5 microl) near glomus tissue located at the main bifurcation of the SLN. The duration of the NaCN response and the number of spikes evoked after application of NaCN were compared in normoxia and hyperoxia (PO2 > 300 mmHg). Hyperoxia significantly reduced the duration and spike number of the NaCN response and a negative linear correlation existed between PO2 and response duration. In addition, hypoxia (PO2 < 60 mmHg) triggered SLN firing. Therefore, we can conclude that the paraganglia of the SLN are not only morphologically similar to the carotid body but are also excited by similar stimuli.

Animals↗
PubMed2006

Effects of combined cholinergic-purinergic block upon cat carotid body chemoreceptors in vitro.

Since acetylcholine (ACh) and ATP have been proposed as excitatory co-transmitters at synapses between glomus cells and sensory nerve endings of the carotid body (CB), we tested such hypothesis by studying the effects of combined cholinergic-purinergic block on the chemosensory activity recorded from cat's carotid bodies perfused and/or superfused in vitro. The preparations were bathed with Tyrode's solution, either normoxic (PO2=98.5+/-13.5 Torr) or hypoxic (PO2=31.8+/-5.2 Torr), and the frequency of chemosensory impulses (fchi) was recorded from the carotid (sinus) nerve. Dose-response curves for fchi increases evoked by intra-stream boluses of acetylcholine, nicotine and ATP were studied. A combination of mecamylamine 2 microM and suramin 50 microM, applied through the perfusate or superfusate, suppressed nicotine- and ATP-induced increases in fchi, but the basal chemosensory activity in normoxia and the chemosensory excitation elicited by hypoxic superfusion were preserved, although variably reduced in most preparations. Thus, in spite of the excitatory effects provoked by applying ACh and ATP to the perfused/superfused CB in vitro, a co-release of these substances cannot account entirely for the chemosensory excitation induced by hypoxic stimulation of the CB.

Acetylcholine↗
PubMed1986

Demethylation of bacterial chemoreceptors is inhibited by attractant stimuli in the complete absence of the regulatory domain of the demethylating enzyme.

The CheB methylesterase catalyzes the demethylation of membrane receptors during chemotaxis in Salmonella typhimurium. The kinetic properties of the full length product of the cheB gene are compared to those of the isolated C-terminal catalytic domain. The fragment has at least a 15-fold higher specific activity than the intact protein. In intact cells receptor demethylation is inhibited by attractants such as L-aspartate. We show here that both forms of the enzyme are similarly inhibited in vitro. Thus, the C-terminal catalytic domain of the CheB protein is sufficient for this aspect of esterase regulation. Inhibition by attractants appears to be caused by changes in receptor conformation rather than by changes in the activity of the demethylating enzyme.

Aspartic Acid↗
PubMed2003

ACh and ATP mediate excitatory transmission in cat carotid identified chemoreceptor units in vitro.

Several molecules have been proposed as excitatory transmitters between glomus (type 1) cells and nerve terminals of petrosal ganglion (PG) neurons in the carotid body (CB). We tested whether ACh and ATP have a role to play as excitatory transmitters in the cat CB by recording intracellularly from identified PG neurons functionally connected to the CB in vitro. PG neurons projecting to the CB were classified according to their intracellular responses as: (a) neurons with humped action potentials (hAP neurons) responding phasically to long-lasting depolarizing pulses (53/67), and (b) neurons with smooth action potentials (non-hAP neurons) that fire tonically during long-lasting depolarizations (14/67). CB stimulation by stop flow and/or acidosis induced activity in 28 of 39 hAP-type neurons, being classified as chemosensory, but in none of the non-hAP neurons. Hexamethonium (10 microM) and suramin (100 microM) reversibly abolished the increased discharges evoked in chemosensory neurons (8/9) by stop flow or acidosis. Moreover, 24 of 27 chemosensory neurons responded to ganglionar application of ACh and ATP, while two neurons responded only to ACh and one to ATP. Mechanical deformation of the carotid sinus induced firing activity in 10 of 13 non-hAP neurons, but in none of the hAP neurons tested. Interestingly, 4/10 non-hAP neurons, which responded to carotid sinus mechanical stimulation also responded to ganglionar application of ATP, but were insensitive to ACh. Present results favor the hypothesis that ACh and ATP are excitatory transmitters in the cat CB, acting-at least-on the PG neuron terminals in the CB.

Acetylcholine↗
PubMed1994

Culture of arterial chemoreceptor cells from adult cats in defined medium.

Recently patch clamp techniques and optical fluorometric techniques have been applied to freshly dissociated or cultured carotid body. However, very few studies have shown the effects of the dissociation and/or culture conditions on the health and function of the cells. The purpose of this study was to develop a culture method which support healthy and functioning carotid body cells from adult cats. Carotid bodies were dissociated with 0.1-0.2% collagenase and gentle trituration. The cells were plated on glass wells coated with poly-D-lysin and Matrigel, and cultured in chemically defined medium. Culture was maintained for up to 37 days without overgrowth of fibroblasts. Glomus cells extended their processes within and from clusters. Single glomus cells acquired the shape of neurons. Glomus cells synthesized dopamine and its secretion increased during exposure of the cells to hypoxia. Tyrosine hydroxylase was expressed throughout the culture period. These results indicate that glomus cells cultured under conditions described here are healthy and function in a manner similar to that in vivo.

Animals↗
PubMed2001

Cytoarchitecture of central chemoreceptors in the mammalian ventral medulla.

We reviewed the previous reports on the fine anatomy of the mammalian ventral medulla with special attention to the cytoarchitecture of the superficial chemosensitive regions to summarize what is known, what is not yet known, and what should be studied in the future. We also reviewed studies on anatomical relationship between neurons and vessels, and morphological studies on dendrites of respiratory or chemosensitive neurons. When we compared the morphological reports on the ventral and dorsal putative chemosensitive regions, similarities were found as follows. Chemosensitive cells were often found not only near the ventral surface but near the dorsal surface of the brainstem. Dendritic projection towards the surface was a common characteristic in the ventral and dorsal chemosensitive neurons. Morphological abnormality in the brainstem of sudden infant death syndrome victims was also summarized. On the basis of the previous reports we discussed the perspective on the future study on central chemoreception. Among various unanswered questions in central chemosensitivity studies, physiological significance of surface cells and surface extending dendrites is the most important topic, and must be thoroughly investigated.

Animals↗
PubMed2001

Olfactory CO(2) chemoreceptors.

Amphibians and reptiles possess CO(2)-sensitive olfactory receptors that cause a dose-dependent decrease in breathing when stimulated by CO(2) concentrations ranging from 0.5 to 8%. In amphibians, it has been shown that inhibition of the enzyme, carbonic anhydrase (CA), attenuates the response of CO(2)-sensitive olfactory receptors to transient changes in nasal CO(2). Histology and electrophysiology studies in frogs show that identification of sites of CA activity can serve as markers for locations of CO(2) chemosensitivity in the olfactory epithelium. There is also growing evidence that CO(2) receptors may be present in the olfactory epithelium of mammals. The objectives of this review are to, (1) summarize the current state of knowledge of olfactory CO(2) receptors in amphibians, reptiles, and mammals; (2) present results from an experiment designed to determine the distribution and density of CA activity within the rat nasal cavity; (3) show results from an experiment that recorded the olfactory receptor response to CO(2) in areas of the rat nasal cavity exhibiting the highest densities of CA activity; and (4) discuss the presumed role of the olfactory CO(2) receptors in the control of breathing and in abnormalities of breathing, such as sudden infant death syndrome (SIDS).

Animals↗