The influence of NaV1.9 on inflammatory mediator‐induced activation of airway vagal nodose C‐fibres was evaluated by comparing responses in wild‐type versus NaV1.9‐/‐ mice. A single‐cell RT‐PCR ...analysis indicated that virtually all nodose C‐fibre neurons expressed NaV1.9 (SCN11A) mRNA. Using extracellular electrophysiological recordings in an isolated vagally innervated mouse trachea–lung preparation, it was noted that mediators acting via G protein‐coupled receptors (PAR2), or ionotropic receptors (P2×3) were 70–85% less effective in evoking action potential discharge in the absence of NaV1.9. However, there was no difference in action potential discharge between wild‐type and NaV1.9‐/‐ when the stimulus was a rapid punctate mechanical stimulus. An analysis of the passive and active properties of isolated nodose neurons revealed no difference between neurons from wild‐type and NaV1.9‐/‐ mice, with the exception of a modest difference in the duration of the afterhyperpolarization. There was also no difference in the amount of current required to evoke action potentials (rheobase) or the action potential voltage threshold. The inward current evoked by the chemical mediator by a P2×3 agonist was the same in wild‐type versus NaV1.9‐/‐ neurons. However, the current was sufficient to evoke action potential only in the wild‐type neurons. The data support the speculation that NaV1.9 could be an attractive therapeutic target for inflammatory airway disease by selectively inhibiting inflammatory mediator‐associated vagal C‐fibre activation.
Key points
Inflammatory mediators were much less effective in activating the terminals of vagal airway C‐fibres in mice lacking NaV1.9.
The active and passive properties of nodose neurons were the same between wild‐type neurons and NaV1.9‐/‐ neurons.
Nerves lacking NaV1.9 responded, normally, with action potential discharge to rapid punctate mechanical stimulation of the terminals or the rapid stimulation of the cell bodies with inward current injections.
NaV1.9 channels could be an attractive target to selectively inhibit vagal nociceptive C‐fibre activation evoked by inflammatory mediators without blocking the nerves’ responses to the potentially hazardous stimuli associated with aspiration.
figure legend We tested the hypothesis that NaV1.9 plays an important role in the excitability of airway vagal nodose C‐fibre. The data reveal that NaV1.9 is important in the activation of nodose C‐fibre terminals evoked by inflammatory mediators that act via G protein‐coupled receptors or ionotropic receptors but less critical in the activation by rapid punctate mechanical stimulation. The presence of NaV1.9 does not influence the membrane properties of the neurons, nor their excitability as assessed by rapid injections of depolarizing current. NaV1.9 provides an intriguing target for treating chronic coughing and the excessive reflex bronchospasm and secretions associated with inflammatory airway disease.
Acute exacerbation of idiopathic pulmonary fibrosis has been defined as an acute, clinically significant, respiratory deterioration of unidentifiable cause. The objective of this international ...working group report on acute exacerbation of idiopathic pulmonary fibrosis was to provide a comprehensive update on the topic. A literature review was conducted to identify all relevant English text publications and abstracts. Evidence-based updates on the epidemiology, etiology, risk factors, prognosis, and management of acute exacerbations of idiopathic pulmonary fibrosis are provided. Finally, to better reflect the current state of knowledge and improve the feasibility of future research into its etiology and treatment, the working group proposes a new conceptual framework for acute respiratory deterioration in idiopathic pulmonary fibrosis and a revised definition and diagnostic criteria for acute exacerbation of idiopathic pulmonary fibrosis.
Key points
Mechanical and metabolic stimuli from contracting muscles evoke reflex increases in blood pressure, heart rate and sympathetic nerve activity. Little is known, however, about the nature of ...the mechano‐gated channels on the thin fibre muscle afferents that contribute to evoke this reflex, termed the exercise pressor reflex.
We determined the effect of GsMTx4, an inhibitor of mechano‐gated Piezo channels, on the exercise pressor reflex evoked by intermittent contraction of the triceps surae muscles in decerebrated, unanaesthetized rats.
GsMTx4 reduced the pressor, cardioaccelerator and renal sympathetic nerve responses to intermittent contraction but did not reduce the pressor responses to femoral arterial injection of compounds that stimulate the metabolically‐sensitive thin fibre muscle afferents.
Expression levels of Piezo2 channels were greater than Piezo1 channels in rat dorsal root ganglia.
Our findings suggest that mechanically‐sensitive Piezo proteins contribute to the generation of the mechanical component of the exercise pressor reflex in rats.
Mechanical and metabolic stimuli within contracting skeletal muscles evoke reflex autonomic and cardiovascular adjustments. In cats and rats, gadolinium has been used to investigate the role played by the mechanical component of this reflex, termed the exercise pressor reflex. Gadolinium, however, has poor selectivity for mechano‐gated channels and exerts multiple off‐target effects. We tested the hypothesis that GsMTX4, a more selective mechano‐gated channel inhibitor than gadolinium and a particularly potent inhibitor of mechano‐gated Piezo channels, reduced the exercise pressor reflex in decerebrate rats. Injection of 10 μg of GsMTx4 into the arterial supply of the hindlimb reduced the peak pressor (control: 24 ± 5, GsMTx4: 12 ± 5 mmHg, P < 0.01), cardioaccelerator and renal sympathetic nerve responses to tendon stretch, a purely mechanical stimulus, but had no effect on the pressor responses to intra‐arterial injection of α,β‐methylene ATP or lactic acid. Moreover, injection of 10 μg of GsMTx4 into the arterial supply of the hindlimb reduced the peak pressor (control: 24 ± 2, GsMTx4: 14 ± 3 mmHg, P < 0.01), cardioaccelerator and renal sympathetic nerve responses to electrically‐induced intermittent hindlimb muscle contractions. By contrast, injection of 10 μg of GsMTx4 into the jugular vein had no effect on the pressor, cardioaccelerator, or renal sympathetic nerve responses to contraction. Quantitative RT‐PCR and western blot analyses indicated that both Piezo1 and Piezo2 channel isoforms were natively expressed in rat dorsal root ganglia tissue. We conclude that GsMTx4 reduced the exercise pressor reflex in decerebrate rats and that the reduction was attributable, at least in part, to its effect on mechano‐gated Piezo channels.
Key points
Mechanical and metabolic stimuli from contracting muscles evoke reflex increases in blood pressure, heart rate and sympathetic nerve activity. Little is known, however, about the nature of the mechano‐gated channels on the thin fibre muscle afferents that contribute to evoke this reflex, termed the exercise pressor reflex.
We determined the effect of GsMTx4, an inhibitor of mechano‐gated Piezo channels, on the exercise pressor reflex evoked by intermittent contraction of the triceps surae muscles in decerebrated, unanaesthetized rats.
GsMTx4 reduced the pressor, cardioaccelerator and renal sympathetic nerve responses to intermittent contraction but did not reduce the pressor responses to femoral arterial injection of compounds that stimulate the metabolically‐sensitive thin fibre muscle afferents.
Expression levels of Piezo2 channels were greater than Piezo1 channels in rat dorsal root ganglia.
Our findings suggest that mechanically‐sensitive Piezo proteins contribute to the generation of the mechanical component of the exercise pressor reflex in rats.
The influence of Na
1.9 on inflammatory mediator-induced activation of airway vagal nodose C-fibres was evaluated by comparing responses in wild-type versus Na
1.9-/- mice. A single-cell RT-PCR ...analysis indicated that virtually all nodose C-fibre neurons expressed Na
1.9 (SCN11A) mRNA. Using extracellular electrophysiological recordings in an isolated vagally innervated mouse trachea-lung preparation, it was noted that mediators acting via G protein-coupled receptors (PAR2), or ionotropic receptors (P2×3) were 70-85% less effective in evoking action potential discharge in the absence of Na
1.9. However, there was no difference in action potential discharge between wild-type and Na
1.9-/- when the stimulus was a rapid punctate mechanical stimulus. An analysis of the passive and active properties of isolated nodose neurons revealed no difference between neurons from wild-type and Na
1.9-/- mice, with the exception of a modest difference in the duration of the afterhyperpolarization. There was also no difference in the amount of current required to evoke action potentials (rheobase) or the action potential voltage threshold. The inward current evoked by the chemical mediator by a P2×3 agonist was the same in wild-type versus Na
1.9-/- neurons. However, the current was sufficient to evoke action potential only in the wild-type neurons. The data support the speculation that Na
1.9 could be an attractive therapeutic target for inflammatory airway disease by selectively inhibiting inflammatory mediator-associated vagal C-fibre activation. KEY POINTS: Inflammatory mediators were much less effective in activating the terminals of vagal airway C-fibres in mice lacking Na
1.9. The active and passive properties of nodose neurons were the same between wild-type neurons and Na
1.9-/- neurons. Nerves lacking Na
1.9 responded, normally, with action potential discharge to rapid punctate mechanical stimulation of the terminals or the rapid stimulation of the cell bodies with inward current injections. Na
1.9 channels could be an attractive target to selectively inhibit vagal nociceptive C-fibre activation evoked by inflammatory mediators without blocking the nerves' responses to the potentially hazardous stimuli associated with aspiration.
We used NaV1.9 knockout (KO) mice to evaluate the role of NaV1.9 in chemical activation of vagal C‐fiber terminals in the mouse lungs. Single‐cell rt‐PCR of lung‐labeled neurons revealed that the ...vast majority of TRPV1 expressing vagal sensory neurons innervating the lungs express NaV1.9 mRNA. The mouse lungs were isolated with the vagus nerves and vagal ganglia intact. Action potentials (APs) were recorded using extracellular electrodes positioned near the relevant cell bodies in the vagal ganglion. The stimuli were applied to the receptive field via perfusion through the mouse trachea. The PAR1 agonist, TFLLR(10mM) evoked 270 ± 62 APs in wild type mice (n=23), but only 85 ± 38 action potentials in NaV1.9 ‐/‐ mice (P< 0.01, n=29). PAR1 is a GPCR stimulus, so we next evaluated a,b‐methylene ATP (1ml, 1µM) that stimulates nodose C‐fibers in the mouse lung via activation of the ionotropic P2X2/3 receptor. a,b‐Methylene ATP evoked 93 ± 18 APs in wildtype mice (n=33), compared to only 13 ± 4 APs the NaV1.9 ‐/‐ mice (P=0.0001, n= 35). The C‐fibers of both WT and NaV1.9 ‐/‐ were equally activated by rapid punctate mechanical stimulation of the receptive field with Von Frey fibers. At the patched clamped cell soma, there was no difference in active or passive electrophysiological properties of nodose neurons isolated from WT versus KO animals; rheobases were also the same with AP threshold averaging 0.34 ± 0.1 and 0.29 ± 0.06 mV/ms, respectively. However, bath‐applied ATP was more effective in evoking action potentials in neurons isolated from WT (40 % responding) vs. KO (0 % responding). The data reveal that NaV1.9 is important in the activation of nodose C‐fiber terminals evoked by inflammatory mediators that act via GPCRs or ionotropic receptors but less critical in the activation by rapid punctate mechanical or electrical stimulation. NaV1.9 provides an intriguing target for treating symptoms caused by inflammatory mediator‐induced C‐fiber activation in the airways, e.g. chronic coughing and excessive reflex bronchospasm and secretions associated with inflammatory airway disease.
NaV1.7 plays a crucial role in inducing and conducting action potentials in pain‐transducing sensory nociceptor fibres, suggesting that NaV1.7 blockers could be effective non‐opioid analgesics. While ...SCN9A is expressed in both sensory and autonomic neurons, its functional role in the autonomic system remains less established. Our single neuron rt‐PCR analysis revealed that 82% of sympathetic neurons isolated from guinea‐pig stellate ganglia expressed NaV1.7 mRNA, with NaV1.3 being the only other tetrodotoxin‐sensitive channel expressed in approximately 50% of neurons. We investigated the role of NaV1.7 in conducting action potentials in postganglionic sympathetic nerves and in the sympathetic adrenergic contractions of blood vessels using selective NaV1.7 inhibitors. Two highly selective NaV1.7 blockers, GNE8493 and PF 05089771, significantly inhibited postganglionic compound action potentials by approximately 70% (P < 0.01), with residual activity being blocked by the NaV1.3 inhibitor, ICA 121431. Electrical field stimulation (EFS) induced rapid contractions in guinea‐pig isolated aorta, pulmonary arteries, and human isolated pulmonary arteries via stimulation of intrinsic nerves, which were inhibited by prazosin or the NaV1 blocker tetrodotoxin. Our results demonstrated that blocking NaV1.7 with GNE8493, PF 05089771, or ST2262 abolished or strongly inhibited sympathetic adrenergic responses in guinea‐pigs and human vascular smooth muscle. These findings support the hypothesis that pharmacologically inhibiting NaV1.7 could potentially reduce sympathetic and parasympathetic function in specific vascular beds and airways.
Key points
82% of sympathetic neurons isolated from the stellate ganglion predominantly express NaV1.7 mRNA.
NaV1.7 blockers inhibit action potential conduction in postganglionic sympathetic nerves.
NaV1.7 blockade substantially inhibits sympathetic nerve‐mediated adrenergic contractions in human and guinea‐pig blood vessels.
Pharmacologically blocking NaV1.7 profoundly affects sympathetic and parasympathetic responses in addition to sensory fibres, prompting exploration into the broader physiological consequences of NaV1.7 mutations on autonomic nerve activity.
figure legend Blocking NaV1.7 pharmacologically demonstrated a profound impact on sympathetic adrenergic responses in both guinea‐pigs and human vascular smooth muscle, leading to either complete abolition or strong inhibition. These findings support the hypothesis that pharmacologically inhibiting NaV1.7 could potentially reduce sympathetic functions in specific vascular beds. ACh: acetylcholine, nACHRs: nicotinic acetylcholine receptor, NA: noradrenaline (norepinephrine), α: alpha‐1 adrenoreceptor.
Na
1.7 plays a crucial role in inducing and conducting action potentials in pain-transducing sensory nociceptor fibres, suggesting that Na
1.7 blockers could be effective non-opioid analgesics. While ...SCN9A is expressed in both sensory and autonomic neurons, its functional role in the autonomic system remains less established. Our single neuron rt-PCR analysis revealed that 82% of sympathetic neurons isolated from guinea-pig stellate ganglia expressed Na
1.7 mRNA, with Na
1.3 being the only other tetrodotoxin-sensitive channel expressed in approximately 50% of neurons. We investigated the role of Na
1.7 in conducting action potentials in postganglionic sympathetic nerves and in the sympathetic adrenergic contractions of blood vessels using selective Na
1.7 inhibitors. Two highly selective Na
1.7 blockers, GNE8493 and PF 05089771, significantly inhibited postganglionic compound action potentials by approximately 70% (P < 0.01), with residual activity being blocked by the Na
1.3 inhibitor, ICA 121431. Electrical field stimulation (EFS) induced rapid contractions in guinea-pig isolated aorta, pulmonary arteries, and human isolated pulmonary arteries via stimulation of intrinsic nerves, which were inhibited by prazosin or the Na
1 blocker tetrodotoxin. Our results demonstrated that blocking Na
1.7 with GNE8493, PF 05089771, or ST2262 abolished or strongly inhibited sympathetic adrenergic responses in guinea-pigs and human vascular smooth muscle. These findings support the hypothesis that pharmacologically inhibiting Na
1.7 could potentially reduce sympathetic and parasympathetic function in specific vascular beds and airways. KEY POINTS: 82% of sympathetic neurons isolated from the stellate ganglion predominantly express Na
1.7 mRNA. Na
1.7 blockers inhibit action potential conduction in postganglionic sympathetic nerves. Na
1.7 blockade substantially inhibits sympathetic nerve-mediated adrenergic contractions in human and guinea-pig blood vessels. Pharmacologically blocking Na
1.7 profoundly affects sympathetic and parasympathetic responses in addition to sensory fibres, prompting exploration into the broader physiological consequences of Na
1.7 mutations on autonomic nerve activity.
Idiopathic pulmonary fibrosis is a progressive, uniformly fatal interstitial lung disease. An acute exacerbation of idiopathic pulmonary fibrosis is an episode of acute respiratory worsening without ...an identifiable etiology. Occult viral infection has been proposed as a possible cause of acute exacerbation.
To use unbiased genomics-based discovery methods to define the role of viruses in acute exacerbation of idiopathic pulmonary fibrosis.
Bronchoalveolar lavage and serum from patients with acute exacerbation of idiopathic pulmonary fibrosis, stable disease, and acute lung injury were tested for viral nucleic acid using multiplex polymerase chain reaction, pan-viral microarray, and high-throughput cDNA sequencing.
Four of forty-three patients with acute exacerbation of idiopathic pulmonary fibrosis had evidence of common respiratory viral infection (parainfluenza n = 1, rhinovirus n = 2, coronavirus n = 1); no viruses were detected in the bronchoalveolar lavage from stable patients. Pan-viral microarrays revealed additional evidence of viral infection (herpes simplex virus n = 1, Epstein-Barr virus n = 2, and torque teno virus TTV n = 12) in patients with acute exacerbation. TTV infection was significantly more common in patients with acute exacerbation than stable controls (P = 0.0003), but present in a similar percentage of acute lung injury controls. Deep sequencing of a subset of acute exacerbation cases confirmed the presence of TTV but did not identify additional viruses.
Viral infection was not detected in most cases of acute exacerbation of idiopathic pulmonary fibrosis. TTV was present in a significant minority of cases, and cases of acute lung injury; the clinical significance of this finding remains to be determined.
A reflex arising from contracting hindlimb muscle is responsible in part for the increases in arterial pressure and heart rate evoked by exercise. The afferent arm of this reflex comprises group III ...and IV afferents. δ-Opioid receptors are expressed predominately on the spinal endings of group III afferents, whereas μ-opioid receptors are expressed predominately on the spinal endings of group IV afferents. Using stimuli that activated group III afferents, namely static contraction, calcaneal tendon stretch, and lactic acid injection into the superficial epigastric artery, we tested the hypothesis that, in rats with either patent or ligated femoral arteries, activation of pre- and postsynaptic δ-opioid receptors in the dorsal horn attenuated pressor reflex responses to these stimuli. In rats with patent arteries or ligated femoral arteries, d-Pen
enkephalin (DPDPE), a δ-opioid agonist injected intrathecally (10 μg in 10 μl), significantly attenuated the pressor responses to contraction, stretch, and lactic acid (all
< 0.05). Naltrindole, a δ-opioid receptor antagonist, prevented the attenuation. In contrast, DPDPE did not attenuate the pressor response to capsaicin injection into the superficial epigastric artery in either group of rats (both
> 0.05). Intrathecal injection of saline (10 μl), the vehicle for DPDPE, had no effect on the pressor responses in either group of rats. We conclude that activation of spinal δ-opioid receptors attenuates reflexes evoked by group III afferents in both freely perfused and ligated rats.
The exercise pressor reflex arises from contracting muscle and is manifested by increases in arterial pressure, heart rate, and cardiac contractility. In patients with peripheral artery disease, the ...exercise pressor reflex is exaggerated. This effect is believed to be caused by a metabolite whose concentration is increased when the working muscles are inadequately perfused. Previous work in rats with simulated peripheral artery disease has shown that pharmacological blockade of acid-sensing ion channel 3 (ASIC3), which is found on group III and IV afferents, prevented the exaggeration of the exercise pressor reflex. Blockade of ASIC3, however, may have off-target effects that preclude a conclusion that ASIC3 plays a role in evoking the reflex in rats with simulated peripheral artery disease. In the present experiments performed in decerebrated rats with simulated peripheral artery disease, we compared the exercise pressor reflex in rats with a functional knockout of the ASIC3 (KO) with the reflex in their wild-type counterparts (WT). We found that the exercise pressor reflex in ASIC3 KO rats was significantly lower than the exercise pressor reflex in their WT counterparts (
< 0.05). ASIC 3 KO rats demonstrated lower pressor responses to intra-arterial injection of diprotonated phosphate (86 mM; pH 6.0), lactic acid (12 mM; pH 2.85), and capsaicin (0.2 μg; pH 7.2) (
< 0.05). In contrast, both ligated WT and ASIC3 KO rats displayed similar pressor responses to tendon stretch (
> 0.05). We conclude that ASIC3 play an important role in evoking the exaggerated exercise pressor reflex in rats with peripheral artery disease.
We used a genetic approach to test the hypothesis that the magnitude of the exercise pressor reflex evoked in ligated ASIC3 KO rats was significantly lower than the magnitude of the exercise pressor reflex evoked in their ligated wild-type (WT) counterparts. The pressor response to contraction in ligated ASIC3 KO rats was significantly smaller than was the pressor response to contraction in ligated WT rats.
PDF
