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Results for “Chemoreceptor Cells”

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At least 523 records · Page 29Linked to original sources
PubMed2001

Glucose sensing in pancreatic beta-cells: a model for the study of other glucose-regulated cells in gut, pancreas, and hypothalamus.

Nutrient homeostasis is known to be regulated by pancreatic islet tissue. The function of islet beta-cells is controlled by a glucose sensor that operates at physiological glucose concentrations and acts in synergy with signals that integrate messages originating from hypothalamic neurons and endocrine cells in gut and pancreas. Evidence exists that the extrapancreatic cells producing and secreting these (neuro)endocrine signals also exhibit a glucose sensor and an ability to integrate nutrient and (neuro)hormonal messages. Similarities in these cellular and molecular pathways provide a basis for a network of coordinated functions between distant cell groups, which is necessary for an appropriate control of nutrient homeostasis. The glucose sensor seems to be a fundamental component of these control mechanisms. Its molecular characterization is most advanced in pancreatic beta-cells, with important roles for glucokinase and mitochondrial oxidative fluxes in the regulation of ATP-sensitive K+ channels. Other glucose-sensitive cells in the endocrine pancreas, hypothalamus, and gut were found to share some of these molecular characteristics. We propose that similar metabolic signaling pathways influence the function of pancreatic alpha-cells, hypothalamic neurons, and gastrointestinal endocrine and neural cells.

Animals↗
PubMed1973

Respiratory chemosensitivity in the medulla oblongata.

Respiratory regulation is considered as a feedback mechanism serving the homeostasis of the hydrogen ion concentration in brain extracellular fluid during rest as well as during exercise. Only in hypoxia the working range of the regulator is shifted in such a way that a sufficient O2 partial pressure is maintained at the cost of hydrogen ion concentration. The main sensing element of the regulator is the ‘central' chemosensitivity. The location of the chemosensitive mechanism in two plaques of a superficial layer of the ventral medulla oblongata is amply discussed. This region is separated from the respiratory centres and provides the centres with a tonic pH sensitive impulse flow. It is not necessary to assume additional chemosensitivity of the centres. In muscular exercise additional impulses reach the centres which are able to compensate the otherwise expected deviation of extracellular pH in brain caused by the increased CO2 production in the body. If the brain is considered as a computer the described homeostatic mechanism may be viewed as assuring the reproducibility of the nerve cells as units of the computer.

Buffers↗
PubMed1993

Chemical control of eukaryotic cell movement: a new model.

Cellular chemotaxis and chemokinesis play important roles in many biological processes. Most continuum mathematical models for these regulatory mechanisms are based on the model of Keller & Segel (1971 a, b), in which cells respond directly to the local concentration of extracellular chemical. We have developed a new model which reflects the receptor-based mechanisms underlying chemical control of cell motion. Our model consists of three coupled partial differential equations, and we use the Boyden chamber (millipore) assay to compare it with a simpler model based on the Keller-Segel approach. The predictions of our model capture the key qualitative features of the experimental data, whereas the simpler model only does so when appropriate functional forms are chosen for the dependence of the transport coefficients on chemical concentration. Using experimental data on the variation of receptor kinetic parameters with temperature, we use our model to predict the effect of decreasing the temperature on both the "leading front" and "migrated cell" measurements taken from Boyden chamber assays. Our results show that changes in the kinetic parameters play a key role in controlling the temperature dependence of cell chemotaxis and chemokinesis.

Chemoreceptor Cells↗
PubMed1991

The vasopressin-like immunoreactive (VPLI) neurons of the locust, Locusta migratoria. II. Physiology.

The two vasopressin-like immunoreactive (VPLI) neurons of the locust, Locusta migratoria, have cell bodies in the suboesophageal ganglion and extensive arborizations throughout the CNS. One of the two peptides responsible for AVP-like immunoreactivity is a vasopressin-related peptide with putative 'diuretic hormone' properties. These neurons also have FLRF-like immunoreactivity, probably due to the FMRF-amide-related peptide. SchistoFLRF-amide, isolated from Schistocerca gregaria. This peptide has cardioinhibitory activity and a dual potentiation/inhibition of slow motoneuron induced muscle-twitch tension. Although haemolymph AVP-like peptide titre fluctuates under various conditions, the mechanism that regulates neurohaemal release of this peptide is not understood. Very little is known of the release of SchistoFLRF-amide. We have used intracellular recording from VPLI neurons in vivo to reveal synaptic inputs that lead to changes in their level of spiking activity, and probably, release of both the AVP-like peptides and SchistoFLRF-amide. This pair of neurosecretory cells has a major, common excitatory input whose sustained rate of activity is inversely related to light intensity; VPLI spiking activity, driven by this input, is greater in the dark than in light. This input is from a pair of descending brain interneurons. Their light-sensitivity persists after ablation of compound eyes, optic lobes and ocelli, showing them to be part of an extra-ocular photoreceptor system. Attempts to record from, and individually stain, the descending neuron have been unsuccessful, although its axon location and diameter in the circumoesophageal connective have been determined. Possible locations for its cell body have been identified; one region, close to the pars intercerebralis, is known to be photosensitive in some insects. Mechanosensory stimuli also lead to brief increases in VPLI spiking activity via the descending interneuron, though this modality rapidly habituates. We detect no changes in VPLI spiking activity that consistently correlate with the osmolality of perfusion salines; such changes might have been expected from their previously proposed role in water homeostasis. Alternative roles for VPLI cells are discussed.

Animals↗
PubMed1994

Vomeronasal system, LHRH, and sex behaviour.

Vomeronasal chemosensory input is important for male hamster mating behavior, especially in inexperienced animals. Experiments reviewed here showed that intracerebroventricular injection of luteinizing hormone-releasing hormone (LHRH) substantially restores mating behavior impaired by removal of vomeronasal organs in inexperienced hamsters. An analogue molecule Ac5-10LHRH, which fails to release luteinizing hormone (LH) from the pituitary, has similar behavioural effects. These findings are consistent with the idea that vomeronasal sensory input may trigger intracerebral release of LHRH which then facilitates mating behaviour. Immunocytochemistry for the immediate-early gene-product Fos, used as an indicator of regional brain activation, indicates a selective activation of central vomeronasal pathways during mating behaviour. Chemosensory and other sensory inputs contribute to activation in medial amygdala and bed-nucleus of stria terminalis, but medial preoptic/anterior hypothalamic area activation appears more closely tied to mating behavior itself. Any of these areas may be sites of interaction between vomeronasal chemosensory input and LHRH-containing cells and fibers.

Amygdala↗
PubMed1962

Electrophysiological studies of a water receptor associated with the taste sensilla of the blow-fly.

Electrophysiological evidence is given that water is the specific stimulus for a fourth sensory cell associated with the taste sensilla of the blowfly. Water elicited impulses from a single cell which responded in two distinct phases: an initial rapid rate of discharge followed by a lesser, sustained steady rate. The latter, in the case of sucrose solutions, was inhibited in direct proportion to the log of the osmotic pressure over a 10(4) range of pressures. Other non-electrolytes inhibited, but the effect could not be simply correlated with parameters of the solutions. Electrolytes inhibited the water response more sharply and at lower concentrations. The inhibition in all cases was not dependent on impulses in the other sensory cells of the taste sensillum.

Animals↗
PubMed1999

Localisation of actin, villin, fimbrin, ezrin and ankyrin in rat taste receptor cells.

Mammalian taste buds consist of 50-150 pear-or spindle-shaped taste receptor cells which contain, at their apical cell surface, a bundle of microvillar projections. The microvilli probably serve to increase the receptive membrane surface of the chemosensory receptor cells. The molecular basis controlling the ultrastructure of taste receptor microvilli is present unknown. In the present study we analysed, by immunostaining at the light and electron microscopic levels and by immunoblotting, components of the cytoskeleton of these microvilli. We show here that taste cell microvilli contain the major cytoskeletal proteins of intestinal microvilli, actin, fimbrin and villin. Another actin-binding, peripheral membrane protein of intestinal microvilli, ezrin, was also localised to taste cell microvilli, where ezrin might play a role, for example, in placement of specific membrane proteins to the microvillus membrane. In search of further linkage proteins, we found ankyrin localised along the basolateral cell surface of taste receptor cells, where ankyrin might be involved in the immobilisation of the Na+, K+-ATPase or other ion-translocating proteins of taste cells to the membrane cytoskeleton.

Actins↗
PubMed1991

Across-fiber patterns may contain a sensory code for stimulus intensity.

Various models for sensory coding have used statistical approaches based on the assumption that the stimulus intensity parameter is represented in the afferent neurons as mean firing frequency. In this paper we question the assumption that this is the only code for intensity. We show that in lobster olfactory receptors narrowly tuned to hydroxyproline, an across-fiber pattern (AFP) code distinguished more concentration levels over a 5 log step range than a response magnitude code and, unlike the latter, was unaffected by response summation time. AFP discrimination of stimulus intensity appears to be based on high inter-cell response variability and low intra-cell response variability.

Animals↗
PubMed1997

Taste reception mechanisms in the blowfly: evidence of amiloride-sensitive and insensitive receptor sites.

The role of amiloride in the labellar responses to various taste stimuli in the blowfly Protophormia terraenovae was studied with the aim of ascertaining whether amiloride-sensitive cation conductances are present in the chemosensory systems of insects. Results include that: 1) amiloride has no effect on the "salt" cell response to any stimulus; 2) amiloride decreases the "sugar" cell response to fructose, but does not affect that to sucrose; 3) the effects of amiloride on the responses of the "water" cell and the "fifth" cell are less clearly definable, due to the probable superimposition of osmotic mechanisms in the former and the poorly known response modalities of the water. In conclusion, amiloride-sensitive receptor sites seem to exist also in insects. However, unlike most vertebrates investigated, they are principally located in the sugar receptor cell, not on the salt cell.

Amiloride↗
PubMed2001

Acid detection by taste receptor cells.

Sourness is a primary taste quality that evokes an innate rejection response in humans and many other animals. Acidic stimuli are the unique sources of sour taste so a rejection response may serve to discourage ingestion of foods spoiled by acid producing microorganisms. The investigation of mechanisms by which acids excite taste receptor cells (TRCs) is complicated by wide species variability and within a species, apparently different mechanisms for strong and weak acids. The problem is further complicated by the fact that the receptor cells are polarized epithelial cells with different apical and basolateral membrane properties. The cellular mechanisms proposed for acid sensing in taste cells include, the direct blockage of apical K(+) channels by protons, an H(+)-gated Ca(2+) channel, proton conduction through apical amiloride-blockable Na(+) channels, a Cl(-) conductance blocked by NPPB, the activation of the proton-gated channel, BNC-1, a member of the Na(+) channel/degenerin super family, and by stimulus-evoked changes in intracellular pH. Acid-induced intracellular pH changes appear to be similar to those reported in other mammalian acid-sensing cells, such as type-I cells of the carotid body, and neurons found in the ventrolateral medulla, nucleus of the solitary tract, the medullary raphe, and the locus coceuleus. Like type-I carotid body cells and brainstem neurons, isolated TRCs demonstrate a linear relationship between intracellular pH (pH(i)) and extracellular pH (pH(o)) with slope, DeltapH(i)/DeltapH(o) near unity. Acid-sensing cells also appear to regulate pH(i) when intracellular pH changes occur under iso-extracellular pH conditions, but fail to regulate their pH when pH(i) changes are induced by decreasing extracellular pH. We shall discuss the current status of proposed acid-sensing taste mechanisms, emphasizing pH-tracking in receptor cells.

Acids↗
PubMed2007

Ionic currents underlying the response of rat dorsal vagal neurones to hypoglycaemia and chemical anoxia.

A proportion of dorsal vagal neurones (DVN) are glucosensors. These cells respond to brief hypoglycaemia either with a K(ATP) channel-mediated hyperpolarization or with depolarization owing to an as yet unknown mechanism. K(ATP) currents are observed not only during hypoglycaemia, but also in response to mitochondrial inhibition. Here we show that similarly to the observations for K(ATP) currents, both hypoglycaemia and inhibition of mitochondrial function elicited a small inward current that persisted in TTX in DVN of rat brainstem slices. Removal of glucose from the bath solution induced this inward current within 50 +/- 4 s in one subpopulation of DVN and in 279 +/- 36 s in another subpopulation. No such subpopulations were observed for the response to mitochondrial inhibition. Biophysical analysis revealed that mitochondrial inhibition or hypoglycaemia inhibited an openly rectifying K+ conductance in 25% of DVN. In the remaining cells, either an increase in conductance, with a reversal potential between -58 and +10 mV, or a parallel inward shift of the holding current was observed. This current most probably resulted from inhibition of the Na+-K+-ATPase and/or the opening of an ion channel. Recordings with electrodes containing 145 mm instead of 5 mm Cl- failed to shift the reversal potential of the inward current, indicating that a Cl- channel was not involved. In summary, glucosensing and non-glucosensing DVN appear to use common electrical pathways to respond to mitochondrial inhibition and to hypoglycaemia. We suggest that differences in glucose metabolism rather than differences in the complement of ion channels distinguish these two cell types.

Action Potentials↗
PubMed1993

Requirement of the carboxyl terminus of a bacterial chemoreceptor for its targeted proteolysis.

The bacterium Caulobacter crescentus yields two different progeny at each cell division; a chemotactically competent swarmer cell and a sessile stalked cell. The chemotaxis proteins are synthesized in the predivisional cell and then partition only to the swarmer cell upon division. The chemoreceptors that were newly synthesized were located at the nascent swarmer pole of the predivisional cell, an indication that asymmetry was established prior to cell division. When the swarmer cell differentiated into a stalked cell, the chemoreceptor was specifically degraded by virtue of an amino acid sequence located at its carboxyl terminus. Thus, a temporally and spatially restricted proteolytic event was a component of this differentiation process.

Amino Acid Sequence↗