Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Chemoreceptor Cells”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1991

Single K+ channels in membrane patches of arterial chemoreceptor cells are modulated by O2 tension.

Type I cells of the carotid body are known to participate in the detection of O2 tension in arterial blood but the primary chemotransduction mechanisms are not well understood. Here we report the existence in excised membrane patches of type I cells of a single K+ channel type modulated by changes in PO2. Open probability of the O2-sensitive K+ channel reversibly decreased by at least 50% on exposure to hypoxia but single-channel conductance (approximately 20 pS) was unaltered. In the range between 70 and 150 mmHg (1 mmHg = 133 Pa) the decrease of single-channel open probability was proportional to the PO2 measured in the vicinity of the membrane patch. The inhibition of K+ channel activity by low PO2 was independent of the presence of non-hydrolyzable guanine triphosphate analogues at the internal face of the membrane. The results indicate that the O2 sensor of type I cells is in the plasma membrane and suggest that environmental O2 interacts directly with the K+ channels.

Animals↗
PubMed1992

Gating of O2-sensitive K+ channels of arterial chemoreceptor cells and kinetic modifications induced by low PO2.

We have studied the kinetic properties of the O2-sensitive K+ channels (KO2 channels) of dissociated glomus cells from rabbit carotid bodies exposed to variable O2 tension (PO2). Experiments were done using single-channel and whole-cell recording techniques. The major gating properties of KO2 channels in excised membrane patches can be explained by a minimal kinetic scheme that includes several closed states (C0 to C4), an open state (O), and two inactivated states (I0 and I1). At negative membrane potentials most channels are distributed between the left-most closed states (C0 and C1), but membrane depolarization displaces the equilibrium toward the open state. After opening, channels undergo reversible transitions to a short-living closed state (C4). These transitions configure a burst, which terminates by channels either returning to a closed state in the activation pathway (C3) or entering a reversible inactivated conformation (I0). Burst duration increases with membrane depolarization. During a maintained depolarization, KO2 channels make several bursts before ending at a nonreversible, absorbing, inactivated state (I1). On moderate depolarizations, KO2 channels inactivate very often from a closed state. Exposure to low PO2 reversibly induces an increase in the first latency, a decrease in the number of bursts per trace, and a higher occurrence of closed-state inactivation. The open state and the transitions to adjacent closed or inactivated states seem to be unaltered by hypoxia. Thus, at low PO2 the number of channels that open in response to a depolarization decreases, and those channels that follow the activation pathway open more slowly and inactivate faster. At the macroscopic level, these changes are paralleled by a reduction in the peak current amplitude, slowing down of the activation kinetics, and acceleration of the inactivation time course. The effects of low PO2 can be explained by assuming that under this condition the closed state C0 is stabilized and the transitions to the absorbing inactivated state I1 are favored. The fact that hypoxia modifies kinetically defined conformational states of the channels suggests that O2 levels determine the structure of specific domains of the KO2 channel molecule. These results help to understand the molecular mechanisms underlying the enhancement of the excitability of glomus cells in response to hypoxia.

Animals↗
PubMed2000

An oxygen-, acid- and anaesthetic-sensitive TASK-like background potassium channel in rat arterial chemoreceptor cells.

The biophysical and pharmacological properties of an oxygen-sensitive background K+ current in rat carotid body type-I cells were investigated and compared with those of recently cloned two pore domain K+ channels. Under symmetrical K+ conditions the oxygen-sensitive whole cell K+ current had a linear dependence on voltage indicating a lack of intrinsic voltage sensitivity. Single channel recordings identified a K+ channel, open at resting membrane potentials, that was inhibited by hypoxia. This channel had a single channel conductance of 14 pS, flickery kinetics and showed little voltage sensitivity except at extreme positive potentials. Oxygen-sensitive current was inhibited by 10 mM barium (57% inhibition), 200 microM zinc (53% inhibition), 200 microM bupivacaine (55% inhibition) and 1 mM quinidine (105 % inhibition). The general anaesthetic halothane (1.5%) increased the oxygen-sensitive K+ current (by 176%). Halothane (3 mM) also stimulated single channel activity in inside-out patches (by 240%). Chloroform had no effect on background K+ channel activity. Acidosis (pH 6.4) inhibited the oxygen-sensitive background K+ current (by 56%) and depolarised type-I cells. The pharmacological and biophysical properties of the background K+ channel are, therefore, analogous to those of the cloned channel TASK-1. Using in situ hybridisation TASK-1 mRNA was found to be expressed in type-I cells. We conclude that the oxygen- and acid-sensitive background K+ channel of carotid body type-I cells is likely to be an endogenous TASK-1-like channel.

Acidosis↗
PubMed2004

Postnatal development of E-4031-sensitive potassium current in rat carotid chemoreceptor cells.

The O2 sensitivity of dissociated type I cells from rat carotid body increases with age until approximately 14-16 days. Hypoxia-induced depolarization appears to be mediated by an O2-sensitive K+ current, but other K+ currents may modulate depolarization. We hypothesized that membrane potential may be stabilized in newborn type I cells by human ether-a-go-go-related gene (HERG)-like K+ currents that inhibit hypoxia-induced depolarization and that a decrease in this current with age could underlie, in part, the developmental increase in type I cell depolarization response to hypoxia. In dissociated type I cells from 0- to 1- and 11- to 16-day-old rats, using perforated patch-clamp and 70 mM K+ extracellular solution, we measured repolarization-induced inward K+ tail currents in the absence and presence of E-4031, a specific HERG channel blocker. This allowed isolation of the E-4031-sensitive HERG-like current. E-4031-sensitive peak currents in type I cells from 0- to- 1-day-old rats were 2.5-fold larger than in cells from 11- to 16-day-old rats. E-4031-sensitive current density in newborn type I cells was twofold greater than in cells from 11- to 16-day-old rats. Under current clamp conditions, E-4031 enhanced hypoxia-induced depolarization in type I cells from 0- to- 1-day-old but not 11- to 16-day-old rats. With use of fura 2 to measure intracellular Ca2+, E-4031 increased the cytosolic Ca2+ concentration response to anoxia in cells from 0- to- 1-day-old but not cells from 11- to 16-day-old rats. E-4031-sensitive K+ currents are present in newborn carotid body type I cells and decline with age. These findings are consistent with a role for E-4031-sensitive K+ current, and possibly HERG-like K+ currents, in the type I cell hypoxia response maturation.

Aging↗
PubMed2001

O(2) modulates large-conductance Ca(2+)-dependent K(+) channels of rat chemoreceptor cells by a membrane-restricted and CO-sensitive mechanism.

Hypoxic inhibition of large-conductance Ca(2+)-dependent K(+) channels (maxiK) of rat carotid body type I cells is a well-established fact. However, the molecular mechanisms of such inhibition and the role of these channels in the process of hypoxic transduction remain unclear. We have examined the mechanisms of interaction of O(2) with maxiK channels exploring the effect of hypoxia on maxiK currents recorded with the whole-cell and the inside-out configuration of the patch-clamp technique. Hypoxia inhibits channel activity both in whole-cell and in excised membrane patches. This effect is strongly voltage- and Ca(2+)-dependent, being maximal at low [Ca(2+)] and low membrane potential. The analysis of single-channel kinetics reveals a gating scheme comprising three open and five closed states. Hypoxia inhibits channel activity increasing the time the channel spends in the longest closed states, an effect that could be explained by a decrease in the Ca(2+) sensitivity of those closed states. Reducing maxiK channels with dithiothreitol (DTT) increases channel open probability, whereas oxidizing the channels with 2,2'-dithiopyridine (DTDP) has the opposite effect. These results suggest that hypoxic inhibition is not related with a reduction of channel thiol groups. However, CO, a competitive inhibitor of O(2) binding to hemoproteins, fully reverts hypoxic inhibition, both at the whole-cell and the single-channel level. We conclude that O(2) interaction with maxiK channels does not require cytoplasmic mediators. Such interaction could be mediated by a membrane hemoprotein that, as an O(2) sensor, would modulate channel activity.

Animals↗
PubMed1989

Ionic currents in dispersed chemoreceptor cells of the mammalian carotid body.

Ionic currents of enzymatically dispersed type I and type II cells of the carotid body have been studied using the whole cell variant of the patch-clamp technique. Type II cells only have a tiny, slowly activating outward potassium current. By contrast, in every type I chemoreceptor cell studied we found (a) sodium, (b) calcium, and (c) potassium currents. (a) The sodium current has a fast activation time course and an activation threshold at approximately -40 mV. At all voltages inactivation follows a single exponential time course. The time constant of inactivation is 0.67 ms at 0 mV. Half steady state inactivation occurs at a membrane potential of approximately -50 mV. (b) The calcium current is almost totally abolished when most of the external calcium is replaced by magnesium. The activation threshold of this current is at approximately -40 mV and at 0 mV it reaches a peak amplitude in 6-8 ms. The calcium current inactivates very slowly and only decreases to 27% of the maximal value at the end of 300-ms pulses to 40 mV. The calcium current was about two times larger when barium ions were used as charge carriers instead of calcium ions. Barium ions also shifted 15-20 mV toward negative voltages the conductance vs. voltage curve. Deactivation kinetics of the calcium current follows a biphasic time course well fitted by the sum of two exponentials. At -80 mV the slow component has a time constant of 1.3 +/- 0.4 ms whereas the fast component, with an amplitude about 20 times larger than the slow component, has a time constant of 0.16 +/- 0.03 ms. These results suggest that type I cells have predominantly fast deactivating calcium channels. The slow component of the tails may represent the activity of a small population of slowly deactivating calcium channels, although other possibilities are considered. (c) Potassium current seems to be mainly due to the activity of voltage-dependent potassium channels, but a small percentage of calcium-activated channels may also exist. This current activates slowly, reaches a peak amplitude in 5-10 ms, and thereafter slowly inactivates. Inactivation is almost complete in 250-300 ms. The potassium current is reversibly blocked by tetraethylammonium. Under current-clamp conditions type I cells can spontaneously fire large action potentials. These results indicate that type I cells are excitable and have a variety of ionic conductances. We suggest a possible participation of these conductances in chemoreception.

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↗
PubMed1992

Time course of K+ current inhibition by low oxygen in chemoreceptor cells of adult rabbit carotid body. Effects of carbon monoxide.

K+ currents recorded from adult rabbit chemoreceptor cells are reversibly inhibited on lowering the pO2 in the bathing solution. Bath application of a hypoxic TTX-containing solution revealed that inhibition of K+ current by low pO2 proceeds faster than TTX inhibition of Na+ currents, the apparent t1/2 being 3.68 and 7.14 s, respectively. Addition of carbon monoxide to the hypoxic gas mixture used to equilibrate the bathing solution reversed the inhibition of K+ currents by approx. 70%.

Animals↗
PubMed1995

Different effects of removing extracellular Ca2+ on cytosolic Ca2+ response to anoxia of sensory neurons and carotid chemoreceptor cells from newborn rabbits.

To study the mechanism of the increases in cytosolic Ca2+ ([Ca2+]i) induced by anoxia, the author examined the effect of removing extracellular Ca2+ on the [Ca2+]i response in cultured nodose ganglion neurons (control) and carotid body glomus cells prepared from newborn rabbits using a fura-2 microfluorimetry. The sensory neurons showed a small increase in [Ca2+]i during anoxia which was not affected by the removal of extracellular Ca2+ or D600. On the other hand, in the chemoreceptor glomus cells, Ca2+ removal eliminated the anoxia-induced large [Ca2+]i increase in 85% of the tested cells (n = 67), and depressed it in the rest. Interestingly, recovery from exposure to an anoxic Ca(2+)-free solution reversibly produced a large and transient rise in [Ca2+]i. The magnitude of this post-anoxic/Ca(2+)-free [Ca2+]i transient correlated with the intensity of the suppression of the [Ca2+]i response to anoxia in Ca(2+)-free solution. Also the [Ca2+]i transient was mostly inhibited by L-type Ca2+ channel blockers (nifedipine and D600), but was not affected by tetrodotoxin. These results suggest that the anoxia-induced large increase in [Ca2+]i were, in most glomus cells, coming from extracellular sources and, in a few cells, from both extracellular sources and from intracellular pools, whereas the slight increase in [Ca2+]i in sensory neurons was probably produced by releasing Ca2+ from intracellular stores. The post-anoxic/Ca(2+)-free [Ca2+]i transient, seen in the chemoreceptor cells alone, may have resulted from modification of the anoxic [Ca2+]i response by Ca2+ removal and involves mostly L-type Ca2+ channels and a few other Ca2+ entry pathways.

Animals↗
PubMed1997

Evidence for two types of nicotinic receptors in the cat carotid body chemoreceptor cells.

Current concepts on the location and functional significance of nicotinic receptors in the carotid body rest on alpha-bungarotoxin binding and autoradiographic studies. Using an in vitro preparation of the cat carotid body whose catecholamine deposits have been labeled by prior incubation with the tritiated natural precursor [3H]tyrosine, we have found that nicotine induces release of [3H]catecholamines in a dose-dependent manner (IC50 = 9.81 microM). We also found that mecamylamine (50 microM) completely abolished the nicotine-induced release, while alpha-bungarotoxin (100 nM; approximately 20 times its binding Kd) only reduced the release by 56%. These findings indicate that chemoreceptor cells, and perhaps other carotid body structures, contain nicotinic receptors that are not sensitive to alpha-bungarotoxin and force a revision of the current concepts on cholinergic mechanisms in the carotid body chemoreception.

3,4-Dihydroxyphenylacetic Acid↗
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

O2-sensitive K+ currents in carotid body chemoreceptor cells from normoxic and chronically hypoxic rats and their roles in hypoxic chemotransduction.

Carotid body-mediated ventilatory increases in response to acute hypoxia are attenuated in animals reared in an hypoxic environment. Normally, O2-sensitive K+ channels in neurosecretory type I carotid body cells are intimately involved in excitation of the intact organ by hypoxia. We have therefore studied K+ channels and their sensitivity to acute hypoxia (PO2 12-20 mmHg) in type I cells isolated from neonatal rats born and reared in normoxic and hypoxic environments. When compared with cells from normoxic rats, K+ current density in cells from hypoxic rats was significantly reduced, whereas Ca2+ current density was unaffected. Charybdotoxin (20 nM) inhibited K+ currents in cells from normoxic rats by approximately 25% but was without significant effect in cells from hypoxic rats. However, hypoxia caused similar, reversible inhibitions of K+ currents in cells from the two groups. Resting membrane potentials (measured at 37 degrees C using the perforated-patch technique) were similar in normoxic and hypoxic rats. However, although acute hypoxia depolarized type I cells of normoxic rats, it was without effect on membrane potential in type I cells from hypoxic animals. Charybdotoxin (20 nM) also depolarized cells from normoxic rats. Our results suggest that type I cells from chronically hypoxic rats, like normoxic rats, possess O2-sensing mechanisms. However, they lack charybdotoxin-sensitive K+ channels that contribute to resting membrane potential in normoxically reared rats, and this appears to prevent them from depolarizing (and hence triggering Ca2+ influx and neurosecretion) during acute hypoxia.

Animals↗
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↗
PubMed2004

Detection of hypoxia-evoked ATP release from chemoreceptor cells of the rat carotid body.

The carotid body (CB) is a chemosensory organ that detects changes in chemical composition of arterial blood and maintains homeostasis via reflex control of ventilation. Thus, in response to a fall in arterial PO(2) (hypoxia), CB chemoreceptors (type I cells) depolarize, and release neurotransmitters onto afferent sensory nerve endings. Recent studies implicate ATP as a key excitatory neurotransmitter released during CB chemoexcitation, but direct evidence is lacking. Here we use the luciferin-luciferase bioluminescence assay to detect ATP, released from rat chemoreceptors in CB cultures, fresh tissue slices, and whole CB. Hypoxia evoked an increase in extracellular ATP, that was inhibited by L-type Ca(2+)channel blockers and reduced by the nucleoside hydrolase, apyrase. Additionally, iberiotoxin (IbTX; 100 nM), a blocker of O(2)-sensitive Ca(2+)-dependent K(+) (BK) channels, stimulated ATP release and largely occluded the effect of hypoxia. These data strongly support a neurotransmitter role for ATP in carotid body function.

Adenosine Triphosphate↗