https://dash.harvard.edu/bitstream/handle/1/29005173/Formulation%20of%20Functionalized%20PLGA-PEG.pdf?sequence=1

Formulation of functionalized PLGA-PEG nanoparticles for in vivo targeted drug delivery

O2 sensing is a fundamental biological process necessary for adaptation of living organisms to variable habitats and physiological situations. Cellular responses to hypoxia can be acute or chronic. Acute responses rely mainly on O2-regulated ion channels, which mediate adaptive changes in cell excitability, contractility, and secretory activity. Chronic responses depend on the modulation of hypoxia-inducible transcription factors, which determine the expression of numerous genes encoding enzymes, transporters and growth factors. O2-regulated ion channels and transcription factors are part of a widely operating signaling system that helps provide sufficient O2 to the tissues and protect the cells against damage due to O2 deficiency. Despite recent advances in the molecular characterization of O2-regulated ion channels and hypoxia-inducible factors, several unanswered questions remain regarding the nature of the O2 sensor molecules and the mechanisms of interaction between the sensors and the effectors. Current models of O2 sensing are based on either a heme protein capable of reversibly binding O2 or the production of oxygen reactive species by NAD(P)H oxidases and mitochondria. Complete molecular characterization of the hypoxia signaling pathways will help elucidate the differential sensitivity to hypoxia of the various cell types and the gradation of the cellular responses to variable levels of PO2. A deeper understanding of the cellular mechanisms of O2 sensing will facilitate the development of new pharmacological tools effective in the treatment of diseases such as stroke or myocardial ischemia caused by localized deficits of O2.

Cellular Mechanism of Oxygen Sensing

The discovery of the sensory nature of the carotid body dates back to the beginning of the 20th century. Following these seminal discoveries, research into carotid body mechanisms moved forward progressively through the 20th century, with many descriptions of the ultrastructure of the organ and stimulus-response measurements at the level of the whole organ. The later part of 20th century witnessed the first descriptions of the cellular responses and electrophysiology of isolated and cultured type I and type II cells, and there now exist a number of testable hypotheses of chemotransduction. The goal of this article is to provide a comprehensive review of current concepts on sensory transduction and transmission of the hypoxic stimulus at the carotid body with an emphasis on integrating cellular mechanisms with the whole organ responses and highlighting the gaps or discrepancies in our knowledge. It is increasingly evident that in addition to hypoxia, the carotid body responds to a wide variety of blood-borne stimuli, including reduced glucose and immune-related cytokines and we therefore also consider the evidence for a polymodal function of the carotid body and its implications. It is clear that the sensory function of the carotid body exhibits considerable plasticity in response to the chronic perturbations in environmental O2 that is associated with many physiological and pathological conditions. The mechanisms and consequences of carotid body plasticity in health and disease are discussed in the final sections of this article.

Peripheral Chemoreceptors: Function and Plasticity of the Carotid Body

The respiratory response to hypoxia in mammals develops from an inhibition of breathing movements in utero into a sustained increase in ventilation in the adult. This ventilatory response to hypoxia (HVR) in mammals is the subject of this review. The period immediately after birth contains a critical time window in which environmental factors can cause long-term changes in the structural and functional properties of the respiratory system, resulting in an altered HVR phenotype. Both neonatal chronic and chronic intermittent hypoxia, but also chronic hyperoxia, can induce such plastic changes, the nature of which depends on the time pattern and duration of the exposure (acute or chronic, episodic or not, etc.). At adult age, exposure to chronic hypoxic paradigms induces adjustments in the HVR that seem reversible when the respiratory system is fully matured. These changes are orchestrated by transcription factors of which hypoxia-inducible factor 1 has been identified as the master regulator. We discuss the mechanisms underlying the HVR and its adaptations to chronic changes in ambient oxygen concentration, with emphasis on the carotid bodies that contain oxygen sensors and initiate the response, and on the contribution of central neurotransmitters and brain stem regions. We also briefly summarize the techniques used in small animals and in humans to measure the HVR and discuss the specific difficulties encountered in its measurement and analysis.

The Ventilatory Response to Hypoxia in Mammals: Mechanisms, Measurement, and Analysis

ATP-dependent priming of the secretory granules precedes Ca(2+)-regulated neuroendocrine secretion, but the exact nature of this reaction is not fully established in all secretory cell types. We have further investigated this reaction in the insulin-secreting pancreatic B-cell and demonstrate that granular acidification driven by a V-type H(+)-ATPase in the granular membrane is a decisive step in priming. This requires simultaneous Cl(-) uptake through granular ClC-3 Cl(-) channels. Accordingly, granule acidification and priming are inhibited by agents that prevent transgranular Cl(-) fluxes, such as 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and an antibody against the ClC-3 channels, but accelerated by increases in the intracellular ATP:ADP ratio or addition of hypoglycemic sulfonylureas. We suggest that this might represent an important mechanism for metabolic regulation of Ca(2+)-dependent exocytosis that is also likely to be operational in other secretory cell types.

Priming of insulin granules for exocytosis by granular Cl(-) uptake and acidification

1. In the whole-cell configuration of the patch clamp technique, isolated rat carotid body type I cells exhibited reversible activation of Cl- currents during cell swelling effected by hypotonic extracellular solutions. 2. Hypotonic solutions evoked outwardly rectifying, non-inactivating currents which showed time-independent activation. The reversal potential (E(rev)) for the hypotonically evoked current was 1.6 +/- 0.6 mV (n = 26). Reduction of extracellular Cl- from 133 to 65.5 mM caused a shift in E(rev) of +14.7 +/- 0.4 mV (n = 5). 3. The swelling-activated Cl- current could not activate when ATP was omitted from the patch pipette or when substituted for the non-hydrolysable ATP analogues 5'-adenylylimidodiphosphate, AMP-PNP (2 mM) or beta, gamma-methylene-adenosine 5'-triphosphate. AMP-PCP (2 mM). The current also failed to activate in the absence of free intracellular Ca2+. 4. The swelling-activated Cl- current was sensitive to blockade by the Cl- channel blockers niflumic acid (300 microM) and 4,4'-diisothiocyanatostilbene-2, 2'-disulphonic acid (DIDS; 200 microM), although the blockade by DIDS was voltage dependent. 5. A similar, non-inactivating, outwardly rectifying Cl- current was evoked by the inclusion of cAMP (200 microM) in the patch pipette. This current could be inhibited by niflumic acid (300 microM), DIDS (200 microM) and hypertonic solutions, and was virtually abolished in the absence of intracellular ATP. 6. In conclusion, carotid body type I cells possess Cl- currents activated by cell swelling and rises in intracellular cAMP concentration. These currents may be involved in cell volume regulation, blood volume and osmolarity regulation and the response of the type I cell to chemostimuli.

Swelling- and cAMP-Activated Cl− Currents in Isolated Rat Carotid Body Type I Cells

1. Amperometric recordings were conducted to investigate the ability of hypoxia and anoxia to evoke quantal catecholamine secretion from isolated type I cells of the rat carotid body. 2. Hypoxia (PO2 8-14 mmHg) consistently failed to evoke catecholamine secretion from type I cells, when cells were perfused either at room temperature (21-24 C) or at 35-37 C, and regardless of whether Hepes- or HCO3-/CO2-buffered solutions were used. 3. Elevating extracellular [K+] caused concentration-dependent secretion from individual type I cells, with a threshold concentration of approximately 25 mM. In the presence of this level of extracellular K+, hypoxia (PO2 8-14 mmHg) caused a marked enhancement of secretion which was fully blocked by 200 microM Cd2+, a non-specific blocker of voltage-gated Ca2+ channels. 4. Anoxia (N2-equilibrated solution containing 0.5 mM dithionite) evoked exocytosis from type I cells when extracellular [K+] was 5 mM. This secretion was completely inhibited by removal of extracellular Ca2+, but was not significantly affected by Cd2+ (200 microM), Ni2+ (2 mM), Zn2+ (1 mM) or nifedipine (2 microM). Secretion was also observed when 0.5 mM dithionite was added to air-equilibrated solutions. 5. Anoxia also evoked secretion from chemoreceptive phaeochromocytoma (PC12) cells, which was wholly Ca2+ dependent, but unaffected by Cd2+ (200 microM). 6. Our results suggest that hypoxia can evoke catecholamine secretion from isolated type I cells, but only in the presence of elevated extracellular [K+]. This may be due to the cells being relatively hyperpolarized following dissociation. In addition, we have shown that dithionite evokes catecholamine release regardless of PO2 levels, and this release is due mainly to an artefactual Ca2+ influx pathway activated in the presence of dithionite.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7793.2000.00719.x

Effects of hypoxia and dithionite on catecholamine release from isolated type I cells of the rat carotid body.

Ca 2+ Channel Currents in Type I Carotid Body Cells of Normoxic and Chronically Hypoxic Neonatal Rats

Protein Kinase C Evokes Quantal Catecholamine Release from PC12 Cells via Activation of L-type Ca2+ Channels

Substitution of extracellular Na + with N-methyl D-glucamine caused marked hyperpolarisation in rat isolated carotid body type I cells, suggesting the presence of a standing Na + conductance. Choline substitution produced smaller hyperpolarisations, whilst Li + was virtually without effect. This Na + conductance was not blocked by amiloride, tetrodotoxin, Zn 2+ or Gd 3+ and did not arise from electrogenic Na-glucose co-transport, since substitution of glucose with sucrose could not mimic the effects of Na + substitution. Hypoxia and acidosis did not modify the tonic Na + influx. Our results suggest that Na + influx provides a constant depolarising influence on type I cells which acts to shift membrane potential beyond that required for initiation of neurosecretion, an essential step in carotid body chemotransduction.

A standing Na+ conductance in rat carotid body type I cells.

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

E. Carpenter

Author Tools

Chat about Author