Role of endothelin and endothelin A-type receptor in adaptation of the carotid body to chronic hypoxia

2002 ◽  
Vol 282 (6) ◽  
pp. L1314-L1323 ◽  
Author(s):  
J. Chen ◽  
L. He ◽  
B. Dinger ◽  
L. Stensaas ◽  
S. Fidone
Keyword(s):  
Carotid Body ◽  
Chronic Hypoxia ◽  
Acute Hypoxia ◽  
Critical Role ◽  
Immunocytochemical Staining ◽  
Type I ◽  
Type I Cells ◽  
I Cells

Chronic exposure in a low-Po 2 environment (i.e., chronic hypoxia, CH) elicits an elevated hypoxic ventilatory response and increased hypoxic chemosensitivity in arterial chemoreceptors in the carotid body. In the present study, we examine the hypothesis that changes in chemosensitivity are mediated by endothelin (ET), a 21-amino-acid peptide, and ETA receptors, both of which are normally expressed by O2-sensitive type I cells. Immunocytochemical staining showed incremental increases in ET and ETAexpression in type I cells after 3, 7, and 14 days of CH (380 Torr). Peptide and receptor upregulation was confirmed in quantitative RT-PCR assays conducted after 14 days of CH. In vitro recordings of carotid sinus nerve activity after in vivo exposure to CH for 1–16 days demonstrated a time-dependent increase in chemoreceptor activity evoked by acute hypoxia. In normal carotid body, the specific ETAantagonist BQ-123 (5 μM) inhibited 11% of the nerve discharge elicited by hypoxia, and after 3 days of CH the drug diminished the hypoxia-evoked discharge by 20% ( P < 0.01). This inhibitory effect progressed to 45% at day 9 of CH and to nearly 50% after 12, 14, and 16 days of CH. Furthermore, in the presence of BQ-123, the magnitude of the activity evoked by hypoxia did not differ in normal vs. CH preparations, indicating that the increased activity was the result of endogenous ET acting on an increasing number of ETA. Collectively, our data suggest that ET and ETA autoreceptors on O2-sensitive type I cells play a critical role in CH-induced increased chemosensitivity in the rat carotid body.

scholarly journals Adaptation to chronic hypoxia involves immune cell invasion and increased expression of inflammatory cytokines in rat carotid body

2009 ◽  
Vol 296 (2) ◽  
pp. L158-L166 ◽  
Author(s):  
X. Liu ◽  
L. He ◽  
L. Stensaas ◽  
B. Dinger ◽  
S. Fidone
Keyword(s):  
Inflammatory Cytokines ◽  
Cell Invasion ◽  
Carotid Body ◽  
Chronic Hypoxia ◽  
Immune Cell ◽  
Cytokine Expression ◽  
Type I ◽  
Type I Cells ◽  
I Cells

Exposure to chronic hypoxia (CH; 3–28 days at 380 Torr) induces adaptation in mammalian carotid body such that following CH an acute hypoxic challenge elicits an abnormally large increase in carotid sinus nerve impulse activity. The current study examines the hypothesis that CH initiates an immune response in the carotid body and that chemoreceptor hyperexcitability is dependent on the expression and action of inflammatory cytokines. CH resulted in a robust invasion of ED1+ macrophages, which peaked on day 3 of exposure. Gene expression of proinflammatory cytokines, IL-1β, TNFα, and the chemokine, monocyte chemoattractant protein-1, was increased >2-fold after 1 day of hypoxia followed by a >2-fold increase in IL-6 on day 3. After 28 days of CH, IL-6 remained elevated >5-fold, whereas expression of other cytokines recovered to normal levels. Cytokine expression was not restricted to immune cells. Studies of cultured type I cells harvested following 1 day of in vivo hypoxia showed elevated transcript levels of inflammatory cytokines. In situ hybridization studies confirmed expression of IL-6 in type I cells and also showed that CH induces IL-6 expression in supporting type II cells. Concurrent treatment of CH rats with anti-inflammatory drugs (ibuprofen or dexamethasone) blocked immune cell invasion and severely reduced CH-induced cytokine expression in carotid body. Drug treatment also blocked the development of chemoreceptor hypersensitivity in CH animals. Our findings indicate that chemoreceptor adaptation involves novel neuroimmune mechanisms, which may alter the functional phenotypes of type I cells and chemoafferent neurons.

Effect of chronic hypoxia on cholinergic chemotransmission in rat carotid body

2005 ◽  
Vol 98 (2) ◽  
pp. 614-619 ◽  
Author(s):  
L. He ◽  
B. Dinger ◽  
S. Fidone
Keyword(s):  
Receptor Antagonist ◽  
Carotid Body ◽  
Nicotinic Receptor ◽  
Chronic Hypoxia ◽  
Prolonged Exposure ◽  
Acute Hypoxia ◽  
Nerve Terminals ◽  
Type I ◽  
Type I Cells ◽  
I Cells

Current views suggest that oxygen sensing in the carotid body occurs in chemosensory type I cells, which excite synaptically apposed chemoafferent nerve terminals in the carotid sinus nerve (CSN). Prolonged exposure in a low-oxygen environment [i.e., chronic hypoxia (CH)] elicits an elevated stimulus-evoked discharge in chemoreceptor CSN fibers (i.e., increased chemosensitivity). In the present study, we evaluated cholinergic chemotransmission in the rat carotid body in an effort to test the hypothesis that CH enhances ACh-mediated synaptic activity between type I cells and chemoafferent nerve terminals. Animals were exposed in a hypobaric chamber (barometric pressure = 380 Torr) for 9–22 days before evaluation of chemoreceptor activity using an in vitro carotid body/CSN preparation. Nerve activity evoked by ACh was significantly larger ( P < 0.01) after CH, suggesting increased expression of cholinergic receptors. Approximately 80% of the CSN impulse activity elicited by ACh (100- or 1,000-μg bolus) in both normal and CH preparations was blocked by the specific nicotinic receptor antagonist mecamylamine (100 μM). CSN activity elicited by acute hypoxia or hypercapnia in normal preparations was likewise blocked (≥80%) in the presence of 100 μM mecamylamine, but after CH the enhanced CSN activity elicited by acute hypoxia or hypercapnia was not reduced in the presence of 100 or 500 μM mecamylamine. A muscarinic receptor antagonist, atropine (10 μM), and a specific nicotinic receptor α7 subunit antagonist, methyllycaconatine (50 nM), blocked ∼50% of the hypoxia-evoked activity in normal preparations but were ineffective after CH. Prolonged exposure to hypoxia appears to dramatically alter chemotransmission in the carotid body, and may induce alternative neurotransmitter mechanisms and/or electrical coupling between type I cells and chemoafferent nerve terminals.

Effect of chronic hypoxia on purinergic synaptic transmission in rat carotid body

2006 ◽  
Vol 100 (1) ◽  
pp. 157-162 ◽  
Author(s):  
L. He ◽  
J. Chen ◽  
B. Dinger ◽  
L. Stensaas ◽  
S. Fidone
Keyword(s):  
Carotid Body ◽  
Chronic Hypoxia ◽  
Cholinergic Receptor ◽  
Nerve Fibers ◽  
Receptor Expression ◽  
Type I ◽  
Simultaneous Exposure ◽  
Type I Cells ◽  
I Cells

Recent studies indicate that chemoafferent nerve fiber excitation in the rat carotid body is mediated by acetylcholine and ATP, acting at nicotinic cholinergic receptors and P2X2 purinoceptors, respectively. We previously demonstrated that, after a 10- to 14-day exposure to chronic hypoxia (CH), the nicotinic cholinergic receptor blocker mecamylamine no longer inhibits rat carotid sinus nerve (CSN) activity evoked by an acute hypoxic challenge. The present experiments examined the effects of CH (9–16 days at 380 Torr) on the expression of P2X2 purinoceptors in carotid body and chemoafferent neurons, as well as the effectiveness of P2X2 receptor blocking drugs on CSN activity evoked by hypoxia. In the normal carotid body, immunocytochemical studies demonstrated a dense plexus of P2X2-positive nerve fibers penetrating lobules of type I cells. In addition, type I cells were lightly stained, indicating P2X2 receptor expression. After CH, the intensity of P2X2 receptor immunostaining was maintained in chemosensory type I cells and in the soma of chemoafferent neurons. P2 receptor expression on type I cells was confirmed by demonstrations of ATP-evoked increased intracellular Ca2+; this response was modulated by simultaneous exposure to hypoxia. In normal preparations, CSN activity evoked by hypoxia in vitro was 65% inhibited in the presence of specific P2X2 receptor antagonists. However, unlike the absence of mecamylamine action after CH, P2X2 antagonists remained effective against hypoxia-evoked activity after CH. Our findings indicate that ATP acting at P2X2 receptors contributes to adjusted chemoreceptor activity after CH, indicating a possible role for purinergic mechanisms in the adaptation of the carotid body in a chronic low-O2 environment.

Characteristics of carotid body chemosensitivity in NADPH oxidase-deficient mice

2002 ◽  
Vol 282 (1) ◽  
pp. C27-C33 ◽  
Author(s):  
L. He ◽  
J. Chen ◽  
B. Dinger ◽  
K. Sanders ◽  
K. Sundar ◽  
...  
Keyword(s):  
Tyrosine Hydroxylase ◽  
Nadph Oxidase ◽  
Carotid Body ◽  
Gene Knockout ◽  
Type I ◽  
Type I Cells ◽  
Carotid Bodies ◽  
Marker Antigen ◽  
I Cells

Various heme-containing proteins have been proposed as primary molecular O2 sensors for hypoxia-sensitive type I cells in the mammalian carotid body. One set of data in particular supports the involvement of a cytochrome b NADPH oxidase that is commonly found in neutrophils. Subunits of this enzyme have been immunocytochemically localized in type I cells, and diphenyleneiodonium, an inhibitor of the oxidase, increases carotid body chemoreceptor activity. The present study evaluated immunocytochemical and functional properties of carotid bodies from normal mice and from mice with a disrupted gp91 phagocytic oxidase (gp91 phox ) DNA sequence gene knockout (KO), a gene that codes for a subunit of the neutrophilic form of NADPH oxidase. Immunostaining for tyrosine hydroxylase, a signature marker antigen for type I cells, was found in groups or lobules of cells displaying morphological features typical of the O2-sensitive cells in other species, and the incidence of tyrosine hydroxylase-immunopositive cells was similar in carotid bodies from both strains of mice. Studies of whole cell K+currents also revealed identical current-voltage relationships and current depression by hypoxia in type I cells dissociated from normal vs. KO animals. Likewise, hypoxia-evoked increases in intracellular Ca2+ concentration were not significantly different for normal and KO type I cells. The whole organ response to hypoxia was evaluated in recordings of carotid sinus nerve activity in vitro. In these experiments, responses elicited by hypoxia and by the classic chemoreceptor stimulant nicotine were also indistinguishable in normal vs. KO preparations. Our data demonstrate that carotid body function remains intact after sequence disruption of the gp91 phox gene. These findings are not in accord with the hypothesis that the phagocytic form of NADPH oxidase acts as a primary O2 sensor in arterial chemoreception.

scholarly journals Modulation of chronic hypoxia-induced chemoreceptor hypersensitivity by NADPH oxidase subunits in rat carotid body

2010 ◽  
Vol 108 (5) ◽  
pp. 1304-1310 ◽  
Author(s):  
L. He ◽  
X. Liu ◽  
J. Chen ◽  
B. Dinger ◽  
L. Stensaas ◽  
...  
Keyword(s):  
Nadph Oxidase ◽  
Carotid Body ◽  
Chronic Hypoxia ◽  
Body Tissue ◽  
Regulatory Subunit ◽  
Type I ◽  
Ros Production ◽  
Tissue Slices ◽  
Type I Cells ◽  
I Cells

Previous studies in our laboratory established that reactive oxygen species (ROS) generated by NADPH oxidase (NOX) facilitate the open state of a subset of K+ channels in oxygen-sensitive type I cells of the carotid body. Thus pharmacological inhibition of NOX or deletion of a NOX gene resulted in enhanced chemoreceptor sensitivity to hypoxia. The present study tests the hypothesis that chronic hypoxia (CH)-induced hypersensitivity of chemoreceptors is modulated by increased NOX activity and elevated levels of ROS. Measurements of dihydroethidium fluorescence in carotid body tissue slices showed that increased ROS production following CH (14 days, 380 Torr) was blocked by the specific NOX inhibitor 4-(2-amino-ethyl)benzenesulfonyl fluoride (AEBSF, 3 μM). Consistent with these findings, in normal carotid body AEBSF elicited a small increase in the chemoreceptor nerve discharge evoked by an acute hypoxic challenge, whereas after 9 days of CH the effect of the NOX inhibitor was some threefold larger ( P < 0.001). Evaluation of gene expression after 7 days of CH showed increases in the isoforms NOX2 (∼1.5-fold) and NOX4 (∼3.8-fold) and also increased presence of the regulatory subunit p47phox (∼4.2-fold). Involvement of p47phox was further implicated in studies of isolated type I cells that demonstrated an ∼8-fold and an ∼11-fold increase in mRNA after 1 and 3 days, respectively, of hypoxia in vivo. These findings were confirmed in immunocytochemical studies of carotid body tissue that showed a robust increase of p47phox in type I cells after 14 days of CH. Our findings suggest that increased ROS production by NOX enzymes in type I cells dampens CH-induced hypersensitivity in carotid body chemoreceptors.

Postnatal maturation of carotid body and type I cell chemoreception in the rat

1999 ◽  
Vol 276 (5) ◽  
pp. L875-L884 ◽  
Author(s):  
Owen S. Bamford ◽  
Laura M. Sterni ◽  
Michael J. Wasicko ◽  
Marshall H. Montrose ◽  
John L. Carroll
Keyword(s):  
Carotid Body ◽  
Carotid Sinus ◽  
Type I ◽  
Carotid Sinus Nerve ◽  
Postnatal Maturation ◽  
Cell Responses ◽  
Type I Cells ◽  
Intracellular Ca ◽  
I Cells

The site of postnatal maturation of carotid body chemoreception is unclear. To test the hypothesis that maturation occurs synchronously in type I cells and the whole carotid body, the development of changes in the intracellular Ca2+ concentration responses to hypoxia, CO2, and combined challenges was studied with fluorescence microscopy in type I cells and compared with the development of carotid sinus nerve (CSN) responses recorded in vitro from term fetal to 3-wk animals. Type I cell responses to all challenges increased between 1 and 8 days and then remained constant, with no multiplicative O2-CO2interaction at any age. The CSN response to hypoxia also matured by 8 days, but CSN responses to CO2 did not change significantly with age. Multiplicative O2-CO2interaction occurred in the CSN response at 2–3 wk but not in younger groups. We conclude that type I cell maturation underlies maturation of the CSN response to hypoxia. However, because development of responses to CO2 and combined hypoxia-CO2 challenges differed between type I cells and the CSN, responses to these stimuli must mature at other, unidentified sites within the developing carotid body.

scholarly journals Chronic hypoxia-induced acid-sensitive ion channel expression in chemoafferent neurons contributes to chemoreceptor hypersensitivity

2011 ◽  
Vol 301 (6) ◽  
pp. L985-L992 ◽  
Author(s):  
X. Liu ◽  
L. He ◽  
B. Dinger ◽  
S. J. Fidone
Keyword(s):  
Inflammatory Cytokines ◽  
Carotid Body ◽  
Chronic Hypoxia ◽  
Immune Cell ◽  
Pdz Domain ◽  
Scaffolding Protein ◽  
Electrophysiological Recording ◽  
Type I ◽  
Type I Cells ◽  
I Cells

Previously we demonstrated that chronic hypoxia (CH) induces an inflammatory condition characterized by immune cell invasion and increased expression of inflammatory cytokines in rat carotid body. It is well established that chronic inflammatory pain induces the expression of acid-sensitive ion channels (ASIC) in primary sensory neurons, where they contribute to hyperalgesia and allodynia. The present study examines the effect of CH on ASIC expression in petrosal ganglion (PG), which contains chemoafferent neurons that innervate oxygen-sensitive type I cells in the carotid body. Five isoforms of ASIC transcript were increased ∼1.5–2.5-fold in PG following exposure of rats to 1, 3, or 7 days of hypobaric hypoxia (380 Torr). ASIC transcript was not increased in the sympathetic superior cervical ganglion (SCG). In the PG, CH also increased the expression of channel-interacting PDZ domain protein, a scaffolding protein known to enhance the surface expression and the low pH-induced current density mediated by ASIC3. Western immunoblot analysis showed that CH elevated ASIC3 protein in PG, but not in SCG or the (sensory) nodose ganglion. ASIC3 transcript was likewise elevated in PG neurons cultured in the presence of inflammatory cytokines. Increased ASIC expression was blocked in CH rats concurrently treated with the nonsteroidal anti-inflammatory drug ibuprofen (4 mg·kg−1·day−1). Electrophysiological recording of carotid sinus nerve (CSN) activity in vitro showed that the specific ASIC antagonist A-317567 (100 μM) did not significantly alter hypoxia-evoked activity in normal preparations but blocked ∼50% of the hypoxic response following CH. Likewise, a high concentration of ibuprofen, which is known to block ASIC1a, reduced hypoxia-evoked CSN activity by ∼50% in CH preparations. Our findings indicate that CH induces inflammation-dependent phenotypic adjustments in chemoafferent neurons. Following CH, ASIC are important participants in chemotransmission between type I cells and chemoafferent nerve terminals, and these proton-gated channels appear to enhance chemoreceptor sensitivity.

Effect of the endothelin receptor antagonist bosentan on chronic hypoxia-induced morphological and physiological changes in rat carotid body

2007 ◽  
Vol 292 (5) ◽  
pp. L1257-L1262 ◽  
Author(s):  
Jia Chen ◽  
Liang He ◽  
Xuemei Liu ◽  
Bruce Dinger ◽  
Larry Stensaas ◽  
...  
Keyword(s):  
Connective Tissue ◽  
Carotid Body ◽  
Structural Changes ◽  
Chronic Hypoxia ◽  
Fold Increase ◽  
Nuclear Antigen ◽  
Type I ◽  
Type I Cells ◽  
Oxygen Sensitive ◽  
I Cells

Previous experiments have repeatedly demonstrated that exposure to chronic hypoxia (CH) elicits remarkable structural changes and chemosensory hypersensitivity in the mammalian carotid body. Moreover, recent studies have shown that CH upregulates the neuroactive peptide, endothelin (ET), in oxygen-sensitive type I cells. The present study examines the possible involvement of ET in adaptation by concurrently exposing rats to hypobaric CH (BP = 380 Torr) and bosentan, a potent nonpeptide antagonist that blocks ETA and ETB receptors. Carotid body weight indicated that 14 days of CH induced organ enlargement, a response that was blunted in bosentan-treated rats (CH: 2.54 ± 0.19-fold increase; CH plus bosentan: 1.92 ± 0.14-fold increase; P < 0.05). Morphometric studies revealed that bosentan substantially eliminated CH-induced hyperplasia of chemosensory cell lobules as well as expansion of the connective tissue matrix. Vascular dilation associated with CH was not altered by the drug. In untreated animals exposed to 3 days of CH, expression of proliferating cell nuclear antigen (PCNA), a marker of mitosis, was increased in lobules of oxygen-sensitive type I cells and in extralobular vascular and connective tissue cells. The incidence of PCNA expression was significantly ( P < 0.05) reduced in bosentan-treated animals. In vitro assessments of carotid sinus nerve (CSN) activity showed that enhancement of basal and hypoxia-evoked chemosensory activity following 9 days of CH was significantly ( P < 0.001) blunted by concurrent treatment with bosentan. Collectively, our data are consistent with the hypothesis that CH-induced adaptation in the carotid body is at least partially mediated by signaling pathways involving ET receptors.

Chronic hypoxia upregulates connexin43 expression in rat carotid body and petrosal ganglion

2002 ◽  
Vol 92 (4) ◽  
pp. 1480-1486 ◽  
Author(s):  
J. Chen ◽  
L. He ◽  
B. Dinger ◽  
L. Stensaas ◽  
S. Fidone
Keyword(s):  
Gap Junction ◽  
Carotid Body ◽  
Chronic Hypoxia ◽  
Type I ◽  
Mrna Levels ◽  
Cx43 Expression ◽  
Type I Cells ◽  
Oxygen Sensitive ◽  
Ganglion Neurons ◽  
I Cells

Recent studies have demonstrated that oxygen-sensitive type I cells in the carotid body express the gap junction-forming protein connexin43 (Cx43). In the present study, we examined the hypothesis that chronic exposure to hypoxia increases Cx43 expression in type I cells as well as in chemoafferent neurons in the petrosal ganglion. Immunocytochemical studies in tissues from normal rats revealed diffuse and granular Cx43-like immunoreactivity in the cytoplasm of type I cells and dense punctate spots of immunoreactive product at the margins of type I cells and near the borders of chemosensory cell lobules. Cx43-like immunoreactivity was not detectable in petrosal ganglion neurons from normal animals. After a 2-wk exposure to hypobaric (380 Torr) hypoxia, Cx43 immunostaining was substantially enhanced in and around type I cells. Moreover, chronic hypoxia elicited the expression of Cx43-like immunoreactivity in the cytoplasm of afferent neurons throughout the petrosal ganglion. Quantitative RT-PCR studies indicate that chronic hypoxia evokes a substantial increase in Cx43 mRNA levels in the carotid body, along with a marked elevation of Cx43 expression in the petrosal ganglion. Increased Cx43 expression and gap junction formation in type I cells and sensory neurons may contribute to carotid body adaptation during sustained stimulation in extreme physiological conditions.

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