56 research outputs found
CO2-dependent opening of an inwardly rectifying K+ channel
No full textCO2 chemosensing is a vital function for the
maintenance of life that helps to control acid–base balance.
Most studies have reported that CO2 is measured via its
proxy, pH. Here we report an inwardly rectifying channel,
in outside-out excised patches from HeLa cells that was
sensitive to modest changes in PCO2 under conditions of
constant extracellular pH. As PCO2 increased, the open
probability of the channel increased. The single-channel
currents had a conductance of 6.7 pS and a reversal
potential of –70 mV, which lay between the K+ and Cl–
equilibrium potentials. This reversal potential was shifted
by +61 mV following a tenfold increase in extracellular
[K+] but was insensitive to variations of extracellular [Cl–].
The single-channel conductance increased with extracellular
[K+]. We propose that this channel is a member of the
Kir family. In addition to this K+ channel, we found that
many of the excised patches also contained a conductance
carried via a Cl–-selective channel. This CO2-sensitive Kir
channel may hyperpolarize excitable cells and provides a
potential mechanism for CO2-dependent inhibition during
hypercapnia
International Consortium to Classify Ageing-related Pathologies (ICCARP) senescence definitions: achieving international consensus.
No full textWith the global increase in ageing populations, a clear understanding of the physiological and pathological changes associated with ageing is vital for advancing research and clinical practice. Following the World Health Organization's decision to classify age-related aetiologies [1], the International Consortium to Classify Ageing-related Pathologies (ICCARP) was established in 2023, led by Cardiff Metropolitan University [2]. The aim of the ICCARP is to develop a systematic and comprehensive classification system for ageingrelated changes including pathologies, diseases, and syndromes. Currently, the ICCARP is in the process Emma Short and Robert TR Huckstepp are Joint first authors
ATP and mechanisms of central CO2 chemosensitivity
No full textATP release from the surface of the ventro-lateral medulla (VLM) is integral to the hypercapnic response in vivo and can be seen in vitro. By employing horizontal slices of the ventral medulla containing the ventral chemosensitive nuclei, I have developed a model that consistently evokes hypercapnia-induced ATP release in vitro. Using this preparation I have studied CO2-triggered ATP release by means of microelectrode biosensors. I conclude that it is the change in PCO2 itself, and not associated pH changes that accompany it, that is directly responsible for eliciting ATP release from the surface of the VLM. In addition ATP release from this region may have a role in the response to hypocapnia as well as hypercapnia. Using pharmacological agents I have demonstrated that gating of connexin hemichannels mediates ATP release. The dorso-ventral distribution of Cx26 ascertained via quantitative PCR and immunofluorescence makes this hemichannel the most likely candidate. Dye loading the cells responsible for ATP release with carboxyfluorescein, which co-localised with Cx26, revealed these cells reside in the pia mater and subpial astrocytes. Application of gap-junction antagonists, with selectivity towards connexin 26, greatly reduced ATP release in response to elevated CO2 in vitro and in vivo and reduced the tone of ATP at the VLM surface. Moreover, by loading Cx26 expressing HeLa cells with ATP, I was able to recapitulate the entire in vivo response. Therefore I propose that ATP is released from sub-pial astrocytes and leptomeningeal cells through connexin 26 hemichannels in response to alterations in PCO2. Here Cx26 performs a dual role, as both the chemosensory transducer and the conduit for ATP release
Your input is a breath of fresh air! A chemosensory microcircuit of medullary raphe and RTN neurons
No full textBreathing is our first act upon birth and the last action we complete before death. The first to last breath taken, is in fact, how we define someone’s life. Since it was first reported that the blood concentration of CO2istightly controlled, and provides the dominant drive to breathe, the search for the cells that regulate it began. It took almost 60 years for the identification of the first central chemosensitive areas, regions within the brain that respond to specific chemical stimuli (such as CO2or its proxy H+), found at the ventrolateral surface of the medulla (VLM). Since then the debate over which cells in these areas are responsible for detectingCO2and signalling its fluctuations to the respiratory oscillators, has been extensive and heated. Chemosensitive cells are thought to have cell bodies located in, or close to, the VLM with dendrites in close apposition to blood vessels to better detect changes in blood gases. Several candidates fulfil this criteria, including the retrotrapezoid nucleus (RTN) and medullary raphe
ATP and mechanisms of central CO2 chemosensitivity
No full textATP release from the surface of the ventro-lateral medulla (VLM) is integral to the hypercapnic response in vivo and can be seen in vitro. By employing horizontal slices of the ventral medulla containing the ventral chemosensitive nuclei, I have developed a model that consistently evokes hypercapnia-induced ATP release in vitro. Using this preparation I have studied CO2-triggered ATP release by means of microelectrode biosensors. I conclude that it is the change in PCO2 itself, and not associated pH changes that accompany it, that is directly responsible for eliciting ATP release from the surface of the VLM. In addition ATP release from this region may have a role in the response to hypocapnia as well as hypercapnia. Using pharmacological agents I have demonstrated that gating of connexin hemichannels mediates ATP release. The dorso-ventral distribution of Cx26 ascertained via quantitative PCR and immunofluorescence makes this hemichannel the most likely candidate. Dye loading the cells responsible for ATP release with carboxyfluorescein, which co-localised with Cx26, revealed these cells reside in the pia mater and subpial astrocytes. Application of gap-junction antagonists, with selectivity towards connexin 26, greatly reduced ATP release in response to elevated CO2 in vitro and in vivo and reduced the tone of ATP at the VLM surface. Moreover, by loading Cx26 expressing HeLa cells with ATP, I was able to recapitulate the entire in vivo response. Therefore I propose that ATP is released from sub-pial astrocytes and leptomeningeal cells through connexin 26 hemichannels in response to alterations in PCO2. Here Cx26 performs a dual role, as both the chemosensory transducer and the conduit for ATP release.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Redefining the components of central CO2 chemosensitivity : towards a better understanding of mechanism
No full textThe field of CO2 chemosensitivity has developed considerably in recent years. There has been a mounting number of competing nuclei proposed as chemosensitive along with an ever increasing list of potential chemosensory transducing molecules. Is it really possible that all of these areas and candidate molecules are involved in the detection of chemosensory stimuli? How do we discriminate rigorously between molecules that are chemosensory transducers at the head of a physiological reflex versus those that just happen to display sensitivity to a chemosensory stimulus? Equally, how do we differentiate between nuclei that have a primary chemosensory function, versus those that are relays in the pathway? We have approached these questions by proposing rigorous definitions for the different components of the chemosensory reflex, going from the salient molecules and ions, through the components of transduction to the identity of chemosensitive cells and chemosensitive nuclei. Our definitions include practical and rigorous experimental tests that can be used to establish the identity of these components. We begin by describing the need for central CO2 chemosensitivity and the problems that the field has faced. By comparing chemosensory mechanisms to those in the visual system we suggest stricter definitions for the components of the chemosensory pathway. We then, considering these definitions, re-evaluate current knowledge of chemosensory transduction, and propose the ‘multiple salient signal hypothesis’ as a framework for understanding the multiplicity of transduction mechanisms and brain areas seemingly involved in chemosensitivity
Release your inhibitions : the role of postinhibitory rebound and synaptic inhibition in the generation of expiratory activity
No full textBreathing in mammals is a fundamental behaviour produced by movements generated and controlled by the central nervous system. The formation of the diaphragm in mammals has led to a unique phenomenon, inspiratory led breathing. In fact, in most mammals at rest, only inspiration is active – expiration is passive. As such research into mechanisms of respiratory rhythm generation has focussed on the inspiratory oscillator, the preBötzinger Complex (preBötC). Whilst we now understand a large number of fundamental properties underlying the behaviour of the preBötC, much less is known about its expiratory counterpart that generates active expiration under conditions of increased respiratory drive; e.g., exercise
CO2-dependent opening of connexin 26 and related beta connexins
No full textWe have previously shown connexin mediated CO2-dependent ATP release from the surface of the medulla oblongata. Given the localization of connexin 26 (Cx26) to the chemosensing areas of the medulla, we have tested in a heterologous expression system (HeLa cells) whether Cx26 may be sensitive to changes in P-CO2. Cx26 responded to an increase in P-CO2 at constant extracellular pH by opening and to a decrease in P-CO2 by closing. Furthermore, Cx26 was partially activated at a physiological P-CO2 of around 40 mmHg. Cx26 in isolated patches responded to changes in P-CO2, suggesting direct CO2 sensitivity of the hemichannel to CO2. Heterologous expression of Cx26 in HeLa cells was sufficient to endow them with the capacity to release ATP in a CO2-sensitive manner. We have examined other heterologously expressed connexins for their ability to respond to changes in P-CO2. The closely related beta connexins Cx30 and Cx32 also displayed sensitivity to changes in P-CO2, but with slightly different characteristics from Cx26. The more distant Cx43 exhibited CO2-dependent closing (possibly mediated through intracellular acidification), while Cx36 displayed no CO2 sensitivity. These surprising findings suggest that connexins may play a hitherto unappreciated variety of signalling roles, and that Cx26 and related beta connexins may impart direct sensitivity to CO2 throughout the brain
Innate sleep apnea in spontaneously hypertensive rats is associated with microvascular rarefaction and neuronal loss in the preBötzinger complex
No full textBACKGROUND:
Sleep apnea (SA) is a major threat to physical health and carries a significant economic burden. These impacts are worsened by its interaction with, and induction of, its comorbidities. SA holds a bidirectional relationship with hypertension, which drives atherosclerosis/arteriolosclerosis, ultimately culminating in vascular dementia.
METHODS:
To enable a better understanding of these sequelae of events, we investigated innate SA and its effects on cognition in adult-aged spontaneously hypertensive rats, which have a range of cardiovascular disorders: plethysmography and electroencephalographic/electromyographic recordings were used to assess sleep-wake state, breathing parameters, and sleep-disordered breathing; immunocytochemistry was used to assess vascular and neural health; the forced alteration Y maze and Barnes maze were used to assess short- and long-term memories, respectively; and an anesthetized preparation was used to assess baroreflex sensitivity.
RESULTS:
Spontaneously hypertensive rats displayed a higher degree of sleep-disordered breathing, which emanates from poor vascular health leading to a loss of preBötzinger Complex neurons. These rats also display small vessel white matter disease, a form of vascular dementia, which may be exacerbated by the SA-induced neuroinflammation in the hippocampus to worsen the related deficits in both long- and short-term memories.
CONCLUSIONS:
Therefore, we postulate that hypertension induces SA through vascular damage in the respiratory column, culminating in neuronal loss in the inspiratory oscillator. This induction of SA, which, in turn, will independently exacerbate hypertension and neural inflammation, increases the rate of vascular dementia
- …
