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At least 775 records · Page 43Linked to original sources
PubMed1988

Temperature effects on CO2-sensitive intrapulmonary chemoreceptors in the lizard, Tupinambis nigropunctatus.

Body temperature (Tb) effects on CO2 responses of 17 intrapulmonary chemoreceptors (IPC) were investigated in 9 anesthetized (pentobarbital; 30 mg/kg) and unidirectionally ventilated tegu lizards (Tupinambis nigropunctatus). At 30 degrees C, all IPC (n = 15) had a stable discharge pattern. At 20 degrees C, IPC discharge (n = 14) was stable at high PCO2 but irregular at low PCO2 and often (10/14) consisted of bursts of activity separated by one or more seconds of quiescence. Responses of IPC to static and dynamic changes in PCO2 were quantified at both Tb and the discharge rate vs PCO2 response curves were compared. Static discharge frequency (fSTAT) decreased as PCO2 increased at both Tb. At 20 degrees C: (1) fSTAT was diminished at all PCO2 levels relative to 30 degrees C; and (2) the slope of the fSTAT vs PCO2 relationship was markedly attenuated. The Q10 was 3.7 +/- 0.5 and was independent of PCO2. The peak discharge associated with a step decrease in PCO2 (dynamic response; fDYN) also decreased as PCO2 increased. At 20 degrees C: (1) fDYN was diminished at all PCO2 levels relative to 30 degrees C; but (2) the slope of the fDYN vs PCO2 relationship was similar at both Tb. The Q10 was 2.6 +/- 0.3 and was significantly less than the Q10 of fSTAT (P less than 0.05). Acute changes in Tb exert large effects on the CO2 response and discharge pattern of IPC; these effects on IPC may be important in ventilatory control at different Tb in lizards.

Animals↗
PubMed1989

The effect of potassium and venous CO2 loading on chemoreceptor firing in anaesthetized cats.

The CO2 production of 5 anaesthetized cats, ventilated to a constant PaCO2 and PaO2 by appropriate alteration of tidal volume and FIO2, was altered by means of an extracorporeal gas exchanger. Afferent chemoreceptor discharge was recorded from a single fibre preparation of the right carotid sinus nerve and the respiratory oscillations in firing were derived over 50 breath (2.5 min) periods. In response to an approximate doubling of CO2 production the discharge oscillation showed an increase in amplitude (P less than 0.05) but no change in mean level. When KCl was infused to produce a mean arterial [K+] of 5.9 mmol/L, while maintaining the same level of CO2 loading, the amplitude of the oscillation increased from 2.9 +/- 0.5 impulses/sec to 5.2 +/- 1.0 impulses/sec (P less than 0.05) and the mean increased from 2.6 +/- 0.4 impulses/sec to 3.9 +/- 0.2 impulses/sec (P less than 0.01). The implications of these findings are discussed.

Action Potentials↗
PubMed1989

Oxygen-sensitive chemoreceptors in the branchio-cardiac veins of the crayfish, Astacus leptodactylus.

Oxygen-sensitive activity was recorded from the branchial nerve of the crayfish Astacus leptodactylus in vitro. After the podobranchial and arthrobranchial nerves branch off to the gill, the branchial nerve terminates in the branchio-cardiac vein wall and its surroundings. When the former 2 branches were cut, irregular spontaneous activity could be recorded from a few fiber preparations innervating the branchio-cardiac vein. The branchio-cardiac vein was superfused or perfused with hypoxic or hyperoxic Ringer solution. Impulse frequency increased in response to hypoxia and decreased in hyperoxia. NaCN and almitrine strongly stimulated nerve activity. Baroreceptor activity was also observed. These response characteristics demonstrate that these receptors are Heymans-type chemoreceptors.

Animals↗
PubMed1989

Responses of vagal efferent fibres to stimulation of gastric mechano- and chemoreceptors in the anaesthetized ferret.

The involvement of gastric tension receptors and mucosal chemoreceptors in vagal reflexes was assessed directly by recording single efferent fibres from the cervical vagus nerve in the urethane anaesthetised ferret. 32/39 fibres responded to distension of the gastric corpus, mainly with excitation of firing, 24/39 fibres responded to antral distension, with a higher proportion showing a reduction in firing. Fifty-seven percent of fibres showed a convergent input from corpus and antrum. The magnitude of these responses was large (usually greater than 50%) and of short latency (less than 1 s). Responses to chemical perfusions in the antrum were seen in 14/31 efferent fibres, most of which showed excitation. Latency of response was variable (5-120 s) and may have been influenced by diffusion through the antral mucous barrier. These data indicate a complex arrangement of vagal reflexes involved in pre-pyloric regulation of gastric emptying by mechanical and chemical stimuli in the lumen.

Action Potentials↗
PubMed1991

Peripheral arterial chemoreceptors and hypertension.

Functional studies in humans and animals with essential hypertension have shown a hyperventilation under resting conditions and striking respiratory and circulatory reactions to hypoxic and hyperoxic tests. There is some evidence that these reactions are due to enhanced activity of the peripheral arterial chemoreceptors. In contrast, in secondary (renal) hypertension such findings could not be observed. Many morphological, morphometrical and biochemical studies have been performed on the carotid bodies of a variety of hypertensive patients and animal models. Whilst their structure and catecholamine content are changed in hypertension, there are many differences in different types of hypertension and, furthermore, a convincing link between the morphological and biochemical findings from the carotid body studies and their functional overactivity has not been shown. Some of these alterations are caused by the elevated blood pressure (e.g. vascular pathology); others are the expression of general disturbances in the hypertensive disease state (e.g. differences in catecholamine content) whilst others are probably of genetic origin but independent of elevated blood pressure (carotid body volume in different rat models of hypertension). This paper reviews the findings on carotid body structure and function in a variety of animal models of hypertension and in primary and secondary human hypertension.

Animals↗
PubMed1991

Reflex responses in adrenal sympathetic nerves to stimulation of glucoreceptors and chemoreceptors in aging rats.

The age-related changes in the sensitivity of reflex responses of adrenal sympathetic nerve activity following stimulation of glucoreceptors and arterial chemoreceptors were investigated in young adult rats 4-5 months old and aged rats 24-26 months old. The sensitivity of the inhibitory reflex responses to stimulation of glucoreceptors and the sensitivity of excitatory reflex responses to systemic hypoxia with end-tidal O2 concentration at 8% and 6% were well maintained in the same ranges in aged rats as in young adult rats. The sensitivity of the excitatory reflex responses to mild systemic hypoxia with end-tidal O2 concentration at 10% increased slightly but significantly in aged rats compared with that in young adult rats.

Adrenal Glands↗
PubMed1992

Expression of D2 dopamine receptor mRNA in the arterial chemoreceptor afferent pathway.

Dopamine is a major neurotransmitter in the arterial chemoreceptor pathway. In the present study we wished to determine if messenger RNAs for dopamine D1 and D2 receptor are expressed in carotid body (type I cells), in sensory neurons of the petrosal ganglion which innervate the carotid body and in sympathetic neurons of the superior cervical ganglion. We failed to detect D1 receptor mRNA in any of these tissues. However, we found that D2 receptor mRNA was expressed by dopaminergic carotid body type I cells. D2 receptor mRNA was also found in petrosal ganglion neurons that innervated the carotid sinus and carotid body. In addition, a large number of sympathetic postganglionic neurons in the superior cervical ganglion expressed D2 receptor mRNA.

Afferent Pathways↗
PubMed1982

A method for localizing intrapulmonary chemoreceptors in the parabronchial mantle of the duck.

1. A method is presented for estimating the location of avian intrapulmonary chemoreceptors within the parabronchial mantle. 2. By determining the discharge frequency of a receptor at known receptor site Pco2's in a nonventilated but perfused lung, the receptor discharge could be calibrated to indicate the receptor site Pco2 during both ventilation and perfusion. 3. The relation among receptor site Pco2, mixed venous Pco2 and inspired Pco2 may be compared with calculated Pco2 profiles along the contact between air capillaries and blood capillaries and the receptor location may be determined as the relative distance between the luminal and peripheral ends of the air capillaries. 4. Of four receptors at the caudal end of a parabronchus, two were located at the terminal end of the air capillary and two along the peripheral half of the air capillary.

Animals↗
PubMed1991

Contrasting effects of HEPES vs HCO3(-)-buffered media on whole-cell currents in cultured chemoreceptors of the rat carotid body.

In this study we compared the effects of physiological bicarbonate/CO2-buffered media (BBM) with the commonly used N-2-hydroxyethylpiperazine-N'-2-ethane-sulfonic acid (HEPES)-buffered media (HBM) on whole-cell currents in cultured rat arterial chemoreceptors (i.e. glomus cells) using the perforated-patch technique. Two separate effects were observed on switching from HBM to BBM. First, in the majority of cells tested (31 of 36) there was an increase in the leakage conductance (ca. 5 fold) and a concomitant increase in channel noise, which in preliminary studies appears to arise from the opening of large-conductance anion channels. Second, there was a reversible decrease in voltage-activated outward K+ current which we attribute to cytoplasmic acidification, catalysed by carbonic anhydrase in glomus cells.

Animals↗
PubMed1992

The role of dihydropyridine-sensitive Ca2+ channels in stimulus-evoked catecholamine release from chemoreceptor cells of the carotid body.

The present study utilized an in vitro preparation of the rabbit carotid body, with tissue catecholamine stores labeled by incubation with 3H-tyrosine. The goal was to characterize pharmacologically the voltage-dependent Ca2+ channels present in the type I (glomus) cells of this arterial chemoreceptor organ, and to elucidate their role as pathways for Ca2+ entry. We found that release of 3H-dopamine induced by high external potassium was over 95% dependent on external calcium concentration and that this release was 90-100% inhibited by the dihydropyridine antagonists, nisoldipine and nitrendipine, and was potentiated by the dihydropyridine agonist, BayK 8644. Therefore, any stimulus-induced, calcium-dependent release of 3H-dopamine that was inhibited by nisoldipine and potentiated by BayK 8644, was considered to be supported by Ca2+ entry into the cells via voltage-dependent Ca2+ channels. Significant differences were observed in the release of 3H-dopamine induced by 75 vs 25 mM K+. On prolonged stimulation, release induced by 75 mM K+ was large and transient, whilst that induced by 25 mM K+, although more moderate, was sustained. The release elicited by 75 mM K+ was inhibited approximately 90% by 1.5 mM Co2+ or 625 nM nisoldipine, while release by 25 mM K+ was completely blocked by 0.6 mM Co2+ or 125 nM nisoldipine. Low PO2-induced release of 3H-dopamine was 95% dependent on Ca2+, and was inhibited by nisoldipine (625 nM) in a manner inversely proportional to the intensity of hypoxic stimulation, i.e. 79% inhibition at a PO2 of 49 Torr, and 20% inhibition at PO2 of 0 Torr. BayK 8644 potentiated the release induced by moderate hypoxic stimuli. Release elicited by high PCO2/low pH, or by Na(+)-propionate or dinitrophenol-containing solutions, was approximately 80% Ca(2+)-dependent, and the dihydropyridines failed to modify this release. It is concluded that type I cells possess voltage-dependent Ca2+ channels sensitive to the dihydropyridines, which in agreement with previous electrophysiological data should be defined as L-type Ca2+ channels. Calcium entry which supports the release of 3H-dopamine elicited by moderate hypoxia should occur mainly through these channels while the release induced by strong hypoxic stimuli will be served by Ca2+ entry which occurs in part via voltage-dependent Ca2+ channels, and in part through an additional pathway, probably a Na+/Ca2+ exchanger.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Chemoreceptors expressed in taste, olfactory and male reproductive tissues.

We have identified three genes encoding previously uncharacterized chemoreceptors expressed in rat sensory and reproductive tissues using a reverse transcriptase polymerase chain reaction strategy. Degenerate oligonucleotides designed from conserved sequences in the rat olfactory receptor gene family were used to amplify candidate receptor gene products expressed in taste tissue. Sequence analysis of three distinct clonal isolates revealed that the gene products from taste bud were 30-75% identical to previously identified olfactory receptor genes. The genomic coding sequences predicted protein structures with seven membrane spanning regions that have strong conservation relative to other members of the G-protein-coupled olfactory receptor gene family. Transcripts for each of the three gene products were detected exclusively in taste, olfactory and male reproductive tissue. Sequence analysis of the polymerase chain reaction products confirmed that identical transcripts were expressed in all three tissues. These findings are the first demonstration that identical olfactory receptor-like gene are expressed in three distinct tissues.

Amino Acid Sequence↗
PubMed2004

Behavioural correlates of phenotypic plasticity in mouthpart chemoreceptor numbers in locusts.

Rearing locusts in an impoverished chemosensory environment leads to fewer chemoreceptors developing on the mouthparts and antennae as adults but the behavioural relevance of these changes remains unknown. To address this question, locusts were reared for the final two larval stadia on either a single, nutritionally near-optimal synthetic food ('plain' pretreatment), or a diet comprising two nutritionally complementary foods containing two added flavours ('mix' pretreatment). Insects reared on the 'mix' diet had a mean 20% more chemosensilla on the maxillary palps than those fed on the 'plain' diet. Following an equilibration period, when all newly moulted adults could feed on two nutritionally complementary foods, insects were food deprived for 2 or 6 h, and then given a test meal of a single balanced food at one of two dilutions whilst their behaviour was recorded. 'Mix'-pretreated locusts had a shorter latency to feed and were more likely to reject the test food upon first contact if deprived for only 2 h; but if they did take a meal it lasted longer and contained fewer pauses. Using sensilla number as a covariate removed the statistical significance of pretreatment regime, indicating that sensilla number, or some close correlate of it, can largely account for the variation in behaviour. This suggests that sensilla numbers are behaviourally relevant; particularly where locusts are not greatly food deprived and faced with marginally acceptable foods.

Animal Feed↗
PubMed2004

Ligand-induced conformational changes in the Bacillus subtilis chemoreceptor McpB determined by disulfide crosslinking in vivo.

Previously, we characterized the organization of the transmembrane (TM) domain of the Bacillus subtilis chemoreceptor McpB using disulfide crosslinking. Cysteine residues were engineered into serial positions along the two helices through the membrane, TM1 and TM2, as well as double mutants in TM1 and TM2, and the extent of crosslinking determined to characterize the organization of the TM domain. In this study, the organization of the TM domain was studied in the presence and absence of ligand to address what ligand-induced structural changes occur. We found that asparagine caused changes in crosslinking rate on all residues along the TM1-TM1' helical interface, whereas the crosslinking rate for almost all residues along the TM2-TM2' interface did not change. These results indicated that helix TM1 rotated counterclockwise and that TM2 did not move in respect to TM2' in the dimer on binding asparagine. Interestingly, intramolecular crosslinking of paired substitutions in 34/280 and 38/273 were unaffected by asparagine, demonstrating that attractant binding to McpB did not induce a "piston-like" vertical displacement of TM2 as seen for Trg and Tar in Escherichia coli. However, these paired substitutions produced oligomeric forms of receptor in response to ligand. This must be due to a shift of the interface between different receptor dimers, within previously suggested trimers of dimers, or even higher order complexes. Furthermore, the extent of disulfide bond formation in the presence of asparagine was unaffected by the presence of the methyl-modification enzymes, CheB and CheR, or the coupling proteins, CheW and CheV, demonstrating that these proteins must have local structural effects on the cytoplasmic domain that is not translated to the entire receptor. Finally, disulfide bond formation was also unaffected by binding proline to McpC. We conclude that ligand-binding induced a conformational change in the TM domain of McpB dimers as an excitation signal that is likely propagated within the cytoplasmic region of receptors and that subsequent adaptational events do not affect this new TM domain conformation.

Animals↗
PubMed2005

Changing the specificity of a bacterial chemoreceptor.

The methyl-accepting chemotaxis proteins are a family of receptors in bacteria that mediate chemotaxis to diverse signals. To explore the plasticity of these proteins, we have developed a simple method for selecting cells that swim to target attractants. The procedure is based on establishing a diffusive gradient in semi-soft agar plates and does not require that the attractant be metabolized or degraded. We have applied this method to select for variants of the Escherichia coli aspartate receptor, Tar, that have a new or improved response to different amino acids. We found that Tar can be readily mutated to respond to new chemical signals. However, the overall change in specificity depended on the target compound. A Tar variant that could detect cysteic acid still showed a strong sensitivity to aspartate, indicating that the new receptor had a broadened specificity relative to wild-type Tar. Tar variants that responded to phenylalanine or N-methyl aspartate, or that had an increased sensitivity to glutamate showed a strong decrease in their response to aspartate. In at least some of the cases, the maximal level of sensitivity that was obtained could not be attributed solely to substitutions within the binding pocket. The new tar alleles and the techniques described here provide a new approach for exploring the relationship between ligand binding and signal transduction by chemoreceptors and for engineering new receptors for applications in biotechnology.

Amino Acid Sequence↗
PubMed2006

Physical responses of bacterial chemoreceptors.

Chemoreceptors of the bacterium Escherichia coli are thought to form trimers of homodimers that undergo conformational changes upon ligand binding and thereby signal a cytoplasmic kinase. We monitored the physical responses of trimers in living cells lacking other chemotaxis proteins by fluorescently tagging receptors and measuring changes in fluorescence anisotropy. These changes were traced to changes in energy transfer between fluorophores on different dimers of a trimer: attractants move these fluorophores farther apart, and repellents move them closer together. These measurements allowed us to define the responses of bare receptor oligomers to ligand binding and compare them to the corresponding response in kinase activity. Receptor responses could be fit by a simple "two-state" model in which receptor dimers are in either active or inactive conformations, from which energy bias and dissociation constants could be estimated. Comparison with responses in kinase-activity indicated that higher-order interactions are dominant in receptor clusters.

Anisotropy↗
PubMed2004

Functional and structural models of pontine modulation of mechanoreceptor and chemoreceptor reflexes.

The dorsolateral and ventrolateral pons (dl-pons, vl-pons) are critical brainstem structures mediating the plasticity of the Hering-Breuer mechanoreflex (HBR) and carotid chemoreflex (CCR). Review of anatomical evidence indicates that dl-pons and vl-pons are connected reciprocally with one another and with medullary nucleus tractus solitarius (NTS) and ventral respiratory group (VRG). With this structural map, functional models of HBR and CCR are proposed in which the respiratory rhythm is modulated by short-term depression (STD) or potentiation (STP) of corresponding primary NTS-VRG and auxiliary pons-VRG excitatory or inhibitory pathways. Behaviorally, STD and STP of respiratory reflexes are akin to non-associative learning such as habituation, sensitization or desensitization to afferent inputs. Computationally, the STD and STP effects amount to signal differentiation and integration in the time domain, or high-pass and low-pass filtering in the frequency domain, respectively. These functional and structural models of pontomedullary signal processing provide a novel conceptual framework that unifies a wealth of experimental observations regarding mechanoreceptor and chemoreceptor reflex control of breathing.

Animals↗
PubMed2005

Imidazole binding reagent diethyl pyrocarbonate (DEPC) inhibits avian intrapulmonary chemoreceptor discharge in vivo.

Data indicate that avian intrapulmonary chemoreceptors (IPC) transduce CO2 stimuli by sensing the products of CO2 hydration, [H+] and [HCO3-]. The alphastat regulation hypothesis of physiological pH sensitivity suggests that proteins sense [H+] through changes in the ionization state of imidazole groups (alphaIm). To test whether imidazole is involved with IPC CO2 sensitivity, we administered diethyl pyrocarbonate (DEPC) intravenously while recording from IPC exposed to varying levels of inspired CO2. At physiological pH, DEPC converts pH sensitive imidazole groups to pH-insensitive N-carbethoxyhistidyl residues. Single cell extracellular neural recordings were made from vagal filaments in anesthetized, unidirectionally ventilated Anas platyrhynchos. Without DEPC, IPC discharge rate was inversely proportional to inspired CO2 with characteristic dynamic responses to rapid CO2 alterations (n = 10). After DEPC treatment (> or = 15 mM), mean sensitivity of IPC discharge to static inspired CO2 levels was decreased 75% (P < 0.05), and mean peak dynamic IPC discharge rate was decreased 80% (P < 0.05). Additionally, we tested whether DEPC might alter IPC discharge by binding imidazole groups in the enzyme carbonic anhydrase (CA), but we found no effect on CA catalytic rate. We conclude that DEPC inhibits IPC CO2 signal transduction by modifying imidazole groups on acid-sensitive proteins other than CA, possibly membrane acid-base exchangers or ion channels. These data support the alphastat regulation hypothesis in IPC CO2 respiratory chemoreception and suggests a more direct link between H+ and membrane excitability.

Action Potentials↗
PubMed2006

Evidence for TREK-like tandem-pore domain channels in intrapulmonary chemoreceptor chemotransduction.

Intrapulmonary chemoreceptors (IPC) are carbon dioxide sensing neurons that innervate the lungs of birds, control breathing pattern, and are inhibited by halothane and intracellular acidosis. TASK and TREK are subfamilies of tandem-pore domain potassium leak channels, important in setting resting membrane potential, that are affected by volatile anesthetics and acidosis. We hypothesized that such channels might underlie signal transduction in IPC. We treated mallard ducks with four volatile anesthetics in increasing concentrations to test their effects on IPC discharge through single cell, extracellular recording from vagal fibers. Isoflurane inhalation attenuated IPC discharge only at 8.25% inspired (alpha=0.05). Halothane attenuated IPC discharge significantly (alpha=0.05) at all treatment levels. Chloroform at 3.8%, 5.6%, and 8.25% significantly attenuated IPC discharge (alpha=0.05). Ether at 1.9%, 2.9%, and 3.8% significantly attenuated IPC discharge (alpha=0.05), abolishing IPC discharge at 3.8% inspired. The pharmacological signature of IPC discharge attenuation suggests that IPC express tandem-pore domain leak channels similar to TREK channels, which are inhibited by intracellular acidosis.

Analysis of Variance↗