An important functional role of persistent Na+ current in carotid body hypoxia transduction

2006 ◽  
Vol 101 (4) ◽  
pp. 1076-1084 ◽  
Author(s):  
Edward Vincent S. Faustino ◽  
David F. Donnelly
Keyword(s):  
Carotid Body ◽  
Acute Hypoxia ◽  
Whole Body ◽  
Conduction Time ◽  
Afferent Neurons ◽  
Patch Clamp Recording ◽  
Peripheral Chemoreceptor ◽  
Whole Cell Patch Clamp ◽  
Old Rats

Systemic hypoxia in mammals is sensed and transduced by the carotid body into increased action potential (AP) frequency on the sinus nerve, resulting in increased ventilation. The mechanism of hypoxia transduction is not resolved, but previous work suggested that fast Na+ channels play an important role in determining the rate and timing of APs (Donnelly, DF, Panisello JM, and Boggs D. J Physiol. 511: 301–311, 1998). We speculated that Na+ channel activity between APs, termed persistent Na+ current ( INaP), is responsible for AP generation that and riluzole and phenytoin, which inhibit this current, would impair organ function. Using whole cell patch clamp recording of intact petrosal neurons with projections to the carotid body, we demonstrated that INaP is present in chemoreceptor afferent neurons and is inhibited by riluzole. Furthermore, discharge frequencies of single-unit, chemoreceptor activity, in vitro, during normoxia (Po2 150 Torr) and during acute hypoxia (Po2 90 Torr) were significantly reduced by riluzole concentrations at or above 5 μM, and by phenytoin at 100 μM, without significant affect on nerve conduction time, AP magnitude (inferred from extracellular field), and AP duration. The effect of both drugs appeared solely postsynaptic because hypoxia-induced catecholamine release in the carotid body was not altered by either drug. The respiratory response of unanesthetized, unrestrained 2-wk-old rats to acute hypoxia (12% inspired O2 fraction), which was measured with whole body plethysmography, was significantly reduced after treatment with riluzole (2 mg/kg ip) and phenytoin (20 mg/kg ip). We conclude that INaP is present in chemoreceptor afferent neurons and serves an important role in peripheral chemoreceptor function and, hence, in the ventilatory response to hypoxia.

scholarly journals Mitochondrial Succinate Metabolism and Reactive Oxygen Species Are Important but Not Essential for Eliciting Carotid Body and Ventilatory Responses to Hypoxia in the Rat

Antioxidants ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 840
Author(s):  
Agnieszka Swiderska ◽  
Andrew M. Coney ◽  
Abdulaziz A. Alzahrani ◽  
Hayyaf S. Aldossary ◽  
Nikolaos Batis ◽  
...  
Keyword(s):  
Carotid Body ◽  
Ex Vivo ◽  
Acute Hypoxia ◽  
Whole Body ◽  
Dimethyl Malonate ◽  
Peripheral Chemoreceptor ◽  
Ventilatory Responses ◽  
Mitochondrial Ros ◽  
O2 Sensing

Reflex increases in breathing in response to acute hypoxia are dependent on activation of the carotid body (CB)—A specialised peripheral chemoreceptor. Central to CB O2-sensing is their unique mitochondria but the link between mitochondrial inhibition and cellular stimulation is unresolved. The objective of this study was to evaluate if ex vivo intact CB nerve activity and in vivo whole body ventilatory responses to hypoxia were modified by alterations in succinate metabolism and mitochondrial ROS (mitoROS) generation in the rat. Application of diethyl succinate (DESucc) caused concentration-dependent increases in chemoafferent frequency measuring approximately 10–30% of that induced by severe hypoxia. Inhibition of mitochondrial succinate metabolism by dimethyl malonate (DMM) evoked basal excitation and attenuated the rise in chemoafferent activity in hypoxia. However, approximately 50% of the response to hypoxia was preserved. MitoTEMPO (MitoT) and 10-(6′-plastoquinonyl) decyltriphenylphosphonium (SKQ1) (mitochondrial antioxidants) decreased chemoafferent activity in hypoxia by approximately 20–50%. In awake animals, MitoT and SKQ1 attenuated the rise in respiratory frequency during hypoxia, and SKQ1 also significantly blunted the overall hypoxic ventilatory response (HVR) by approximately 20%. Thus, whilst the data support a role for succinate and mitoROS in CB and whole body O2-sensing in the rat, they are not the sole mediators. Treatment of the CB with mitochondrial selective antioxidants may offer a new approach for treating CB-related cardiovascular–respiratory disorders.

scholarly journals Ventilatory and carotid body chemoreceptor responses to purinergic P2X receptor antagonists in newborn rats

2011 ◽  
Vol 110 (1) ◽  
pp. 83-94 ◽  
Author(s):  
Lalah M. Niane ◽  
David F. Donnelly ◽  
Vincent Joseph ◽  
Aida Bairam
Keyword(s):  
Carotid Body ◽  
Discharge Rate ◽  
Hypoxic Condition ◽  
P2x Receptor ◽  
Whole Body ◽  
Newborn Rats ◽  
Adult Rats ◽  
Before And After ◽  
Old Rats

Adenosine triphosphate, acting through purinergic P2X receptors, has been shown to stimulate ventilation and increase carotid body chemoreceptor activity in adult rats. However, its role during postnatal development of the ventilatory response to hypoxia is yet unknown. Using whole body plethysmography, we measured ventilation in normoxia and in moderate hypoxia (12% fraction of inspired O2, 20 min) before and after intraperitoneal injection of suramin (P2X2 and P2X3 receptor antagonist, 40 mg/kg) in 4-, 7-, 12-, and 21-day-old rats. Suramin reduced baseline breathing (∼20%) and the response to hypoxia (∼30%) in all rats, with a relatively constant effect across ages. We then tested the effect of the specific P2X3 antagonist, A-317491 (150 mg/kg), in rats aged 4, 7, and 21 days. As with suramin, A-317491 reduced baseline ventilation (∼55%) and the hypoxic response (∼40%) at all ages studied. Single-unit carotid body chemoreceptor activity was recorded in vitro in 4-, 7-, and 21-day-old rats. Suramin (100 μM) and A-317491 (10 μM) significantly depressed the sinus nerve chemosensory discharge rate (∼80%) in normoxia (Po2 ∼150 Torr) and hypoxia (Po2 ∼60 Torr), and this decrease was constant across ages. We conclude that, in newborn rats, P2X purinergic receptors are involved in the regulation of breathing under basal and hypoxic condition, and P2X3-containing receptors play a major role in carotid body function. However, these effects are not age dependent within the age range studied.

Perinatal hyperoxia for 14 days increases nerve conduction time and the acute unitary response to hypoxia of rat carotid body chemoreceptors

2005 ◽  
Vol 99 (1) ◽  
pp. 114-119 ◽  
Author(s):  
David F. Donnelly ◽  
Insook Kim ◽  
Claire Carle ◽  
John L. Carroll
Keyword(s):  
Functional Impairment ◽  
Nerve Conduction ◽  
Single Unit ◽  
Acute Hypoxia ◽  
Adult Life ◽  
Perinatal Period ◽  
Postnatal Period ◽  
Conduction Time ◽  
Activity Levels

Hyperoxia in the immediate perinatal period, but not in adult life, is associated with a life-long impairment of the ventilatory response to acute hypoxia. This effect is attributed to a functional impairment of peripheral chemoreceptors, including a reduction in the number of chemoreceptor afferent fibers and a reduction in “whole nerve” afferent activity. The purpose of the present study was to assess the activity levels of single chemoreceptor units in the immediate posthyperoxic period to determine whether functional impairment extended to single chemoreceptor units and whether the impairment was only induced by hyperoxia exposure in the immediate postnatal period. Two groups of rat pups were exposed to 60% inspired O2 fraction for 2 wk at ages 0–14 days and 14–28 days, at which time single-unit activities were isolated and recorded in vitro. Compared with control pups, hyperoxia-treated pups had a 10-fold reduction in baseline (normoxia) spiking activity. Peak unit responses to 12, 5, and 0% O2 were reduced and nerve conduction time was significantly slower in both hyperoxia-treated groups compared with control groups. We conclude that 1) hyperoxia greatly reduces single-unit chemoreceptor activities during normoxia and acute hypoxia, 2) the treatment effect is not limited to the immediate newborn period, and 3) at least part of the impairment may be due to changes in the afferent axonal excitability.

Chemoreceptor nerve excitation may not be proportional to catecholamine secretion

1996 ◽  
Vol 81 (2) ◽  
pp. 657-664 ◽  
Author(s):  
D. F. Donnelly
Keyword(s):  
Carotid Body ◽  
Catecholamine Secretion ◽  
Nerve Activity ◽  
Peripheral Chemoreceptor ◽  
Carotid Bodies ◽  
Carbon Fiber Microelectrodes ◽  
S Peak ◽  
Nerve Excitation ◽  
Catecholamine Levels

Enhanced catecholamine secretion from the carotid body glomus cells is hypothesized to play an essential role in mediating the peripheral chemoreceptor response to hypoxia. To test aspects of this hypothesis, the relationship between catecholamine secretion and nerve activity was examined during repetitive hypoxia stimuli and after catecholamine depletion with reserpine. Single-fiber afferent serve activity was measured along with an estimate of free tissue catecholamine by using Nafion-coated carbon-fiber microelectrodes placed in rat carotid bodies in vitro. Baseline and stimulated nerve and catecholamine levels were quantified during repetitive stimulation (anoxia of 1-min duration; PO2 = 0 Torr at nadir, repeated each 200 s). Peak stimulated catecholamine progressively decreased from 26.4 +/- 2.6 microM for the first stimulus to 7.5 +/- 0.9 microM for the fifth stimulus (n = 15), but peak nerve activity was much less affected (23.0 +/- 1.9 Hz, first trial; 19.9 +/- 1.4 Hz, fifth trial). An exposure to moderate hypoxia (approximately 80 Torr) before the repetitive anoxia stimuli produced catecholamine levels comparable to those obtained during repetitive anoxia, but peak nerve activity was significantly less (22.5 +/- 3.4 vs. 12.7 +/- 2.1 Hz). Pretreatment with reserpine (1 mg/100 g) resulted in a large reduction in the average hypoxia-induced catecholamine response (1.4 +/- 0.3 microM, n = 9), but peak nerve activity was not different from nontreated controls. These results demonstrate an independence between carotid body catecholamine secretion and nerve activity, suggesting that nerve excitation is, at least, partially mediated through pathways independent of granule secretion.

scholarly journals Morphine-induced synaptic plasticity in the VTA is reversed by HDAC inhibition

2016 ◽  
Vol 116 (3) ◽  
pp. 1093-1103 ◽  
Author(s):  
Michael E. Authement ◽  
Ludovic D. Langlois ◽  
Haifa Kassis ◽  
Shawn Gouty ◽  
Matthieu Dacher ◽  
...  
Keyword(s):  
Behavioral Plasticity ◽  
Drugs Of Abuse ◽  
Patch Clamp Recording ◽  
Whole Cell Patch Clamp ◽  
Synaptic Changes ◽  
Induced Changes ◽  
And Behavior ◽  
H3 Acetylation

Dopamine (DA) dysfunction originating from the ventral tegmental area (VTA) occurs as a result of synaptic abnormalities following consumption of drugs of abuse and underlies behavioral plasticity associated with drug abuse. Drugs of abuse can cause changes in gene expression through epigenetic mechanisms in the brain that underlie some of the lasting neuroplasticity and behavior associated with addiction. Here we investigated the function of histone acetylation and histone deacetylase (HDAC)2 in the VTA in recovery of morphine-induced synaptic modifications following a single in vivo exposure to morphine. Using a combination of immunohistochemistry, Western blot, and whole cell patch-clamp recording in rat midbrain slices, we show that morphine increased HDAC2 activity in VTA DA neurons and reduced histone H3 acetylation at lysine 9 (Ac-H3K9) in the VTA 24 h after the injection. Morphine-induced synaptic changes at glutamatergic synapses involved endocannabinoid signaling to reduce GABAergic synaptic strength onto VTA DA neurons. Both plasticities were recovered by in vitro incubation of midbrain slices with a class I-specific HDAC inhibitor (HDACi), CI-994, through an increase in acetylation of histone H3K9. Interestingly, HDACi incubation also increased levels of Ac-H3K9 and triggered GABAergic and glutamatergic plasticities in DA neurons of saline-treated rats. Our results suggest that acute morphine-induced changes in VTA DA activity and synaptic transmission engage HDAC2 activity locally in the VTA to maintain synaptic modifications through histone hypoacetylation.

scholarly journals Functional and Pharmacological Evaluation of a Novel SCN2A Variant Linked to Early-onset Epilepsy

2020 ◽  
Author(s):  
Scott K. Adney ◽  
John J. Millichap ◽  
Jean-Marc DeKeyser ◽  
Tatiana Abramova ◽  
Christopher H. Thompson ◽  
...  
Keyword(s):  
Drug Response ◽  
Time Course ◽  
Voltage Dependence ◽  
De Novo ◽  
Patch Clamp Recording ◽  
Variants Of Unknown Significance ◽  
Whole Cell Patch Clamp ◽  
Genetic Features ◽  
Resurgent Current

ABSTRACTObjectiveWe identified a novel de novo SCN2A variant (M1879T) associated with infantile-onset epilepsy that responded dramatically to sodium channel blocker antiepileptic drugs. We analyzed the functional and pharmacological consequences of this variant to establish pathogenicity, and to correlate genotype with phenotype and clinical drug response.MethodsThe clinical and genetic features of an infant boy with epilepsy are presented. We investigated the effect of the variant using heterologously expressed recombinant human NaV1.2 channels. We performed whole-cell patch clamp recording to determine the functional consequences and response to carbamazepine.ResultsThe M1879T variant caused disturbances in channel inactivation including substantially depolarized voltage-dependence of inactivation, slower time course of inactivation, and enhanced resurgent current that collectively represent a gain-of-function. Carbamazepine partially normalized the voltage-dependence of inactivation and produced use-dependent block of the variant channel at high pulsing frequencies. Carbamazepine also suppresses resurgent current conducted by M1879T channels, but this effect was explained primarily by reducing the peak transient current. Molecular modeling suggests that the M1879T variant disrupts contacts with nearby residues in the C-terminal domain of the channel.InterpretationOur study demonstrates the value of conducting functional analyses of SCN2A variants of unknown significance to establish pathogenicity and genotype-phenotype correlations. We also show concordance of in vitro pharmacology using heterologous cells with the drug response observed clinically in a case of SCN2A-associated epilepsy.

In Vitro Properties of Neurons in the Rat Pretectal Nucleus of the Optic Tract

2007 ◽  
Vol 97 (5) ◽  
pp. 3574-3584 ◽  
Author(s):  
N. Prochnow ◽  
P. Lee ◽  
W. C. Hall ◽  
M. Schmidt
Keyword(s):  
Fluorescent Dyes ◽  
Optic Tract ◽  
Cell Populations ◽  
Patch Clamp Recording ◽  
Visual Activity ◽  
Optokinetic Reflex ◽  
Whole Cell Patch Clamp ◽  
Pretectal Nucleus ◽  
Efferent Projections

The nucleus of the optic tract (NOT) has been implicated in the initiation of the optokinetic reflex (OKR) and in the modulation of visual activity during saccades. The present experiments demonstrate that these two functions are served by separate cell populations that can be distinguished by differences in both their cellular physiology and their efferent projections. We compared the response properties of NOT cells in rats using target-directed whole cell patch-clamp recording in vitro. To identify the cells at the time of the recording experiments, they were prelabeled by retrograde axonal transport of WGA-apo-HRP-gold (15 nm), which was injected into their primary projection targets, either the ipsilateral superior colliculus (iSC), or the contralateral NOT (cNOT), or the ipsilateral inferior olive (iIO). Retrograde labeling after injections in single animals of either WGA-apo-HRP-gold with different particle sizes (10 and 20 nm) or two different fluorescent dyes distinguished two NOT cell populations. One projects to both the iSC and cNOT. These cells are spontaneously active in vitro and respond to intracellular depolarizations with temporally regular tonic firing. The other population projects to the iIO and consists of cells that show no spontaneous activity, respond phasically to intracellular depolarization, and show irregular firing patterns. We propose that the spontaneously active pathway to iSC and cNOT is involved in modulating the level of visual activity during saccades and that the phasically active pathway to iIO provides a short-latency relay from the retina to premotor mechanisms involved in reducing retinal slip.

Modulatory effects of 5-hydroxytryptamine on voltage-activated currents in cultured antennal lobe neurones of the sphinx moth Manduca sexta.

1995 ◽  
Vol 198 (3) ◽  
pp. 613-627 ◽  
Author(s):  
A R Mercer ◽  
J H Hayashi ◽  
J G Hildebrand
Keyword(s):  
Manduca Sexta ◽  
Adult Development ◽  
Antennal Lobe ◽  
Ionic Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Recording ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
Reversible Reduction

The modulatory effects of 5-hydroxytryptamine (5-HT or serotonin) on voltage-gated currents in central olfactory neurones of the moth Manduca sexta have been examined in vitro using whole-cell patch-clamp recording techniques. Central olfactory neurones were dissociated from the antennal lobes of animals at stage 5 of the 18 stages of metamorphic adult development. The modulatory actions of 5-HT on voltage-activated ionic currents were examined in a subset of morphologically identifiable antennal lobe neurones maintained for 2 weeks in primary cell culture. 5-HT caused reversible reduction of both a rapidly activating A-type K+ current and a relatively slowly activating K+ current resembling a delayed rectifier-type conductance. 5-HT also reduced the magnitude of voltage-activated Ca2+ influx in these cells. The functional significance of 5-HT-modulation of central neurones is discussed.

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.

Early anoxia-induced vesicular glutamate release results from mobilization of calcium from intracellular stores

1993 ◽  
Vol 70 (1) ◽  
pp. 1-7 ◽  
Author(s):  
A. N. Katchman ◽  
N. Hershkowitz
Keyword(s):  
Calcium Influx ◽  
Glutamate Release ◽  
Hippocampal Slices ◽  
Calcium Currents ◽  
Patch Clamp Recording ◽  
Ca1 Neurons ◽  
Whole Cell Patch Clamp ◽  
Mepsc Frequency ◽  
Synaptic Changes

1. The cause of the increased frequency of glutamatergic miniature excitatory postsynaptic currents (mEPSCs) resulting from anoxia was investigated in CA1 neurons of the in vitro rat hippocampal slice. These neurons were examined by whole-cell patch-clamp recording, and hypoxia was induced by switching the perfusion of the slice from oxygenated artificial cerebral spinal fluid (ACSF) to ACSF saturated with 95% N2-5% O2. Except where noted, experiments were carried out in ACSF containing 1 microM tetrodotoxin (TTX). 2. Although anoxia resulted in a significant increase in the frequency of mEPSCs, the amplitude, rise time, and half-decay time of the mEPSCs were unchanged. This increase in frequency indicates that there is a change in presynaptic neurotransmitter release mechanisms, probably an increase in calcium concentration, soon after the onset of anoxia. The unchanged kinetics and amplitude of the mEPSCs indicate that anoxic-induced synaptic changes are not a result of changes in the postsynaptic glutamate receptor. 3. When hippocampal slices were exposed to anoxic conditions in ACSF with calcium excluded, an increase in mEPSC frequency equal to that in normal ACSF was observed. When 0.2 mM of CdCl2 was added to the zero-calcium ACSF, anoxia still resulted in increases in mEPSC frequency equal to those of normal ACSF. It is therefore concluded that the anoxia-induced increase in mEPSC frequency does not result from an increase in a transmembrane calcium influx. The zero-calcium plus 0.2 mM CdCl2 ACSF solution completely abolished orthodromically elicited synaptic potential (in the absence of TTX), indicating that calcium currents that mediate normal orthodromic transmitter release were completely abolished in the latter experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

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