Carotid body cell culture and selective growth of glomus cells

Stem Cell Niche in the Mammalian Carotid Body

Accumulating evidence suggests that the mammalian carotid body (CB) constitutes a neurogenic center that contains a functionally active germinal niche. A variety of transcription factors is required for the generation of a precursor cell pool in the developing CB. Most of them are later silenced in their progeny, thus allowing for the maturation of the differentiated neurons. In the adult CB, neurotransmitters and vascular cytokines released by glomus cells upon exposure to chronic hypoxia act as paracrine signals that induce proliferation and differentiation of pluripotent stem cells, neuronal and vascular progenitors. Key proliferation markers such as Ki-67 and BrdU are widely used to evaluate the proliferative status of the CB parenchymal cells in the initial phase of this neurogenesis. During hypoxia sustentacular cells which are dormant cells in normoxic conditions can proliferate and differentiate into new glomus cells. However, more recent data have revealed that the majority of the newly formed glomus cells is derived from the glomus cell lineage itself. The mature glomus cells express numerous trophic and growth factors, and their corresponding receptors, which act on CB cell populations in autocrine or paracrine ways. Some of them initially serve as target-derived survival factors and then as signaling molecules in developing vascular targets. Morphofunctional insights into the cellular interactions in the CB stem cell microenvironment can be helpful in further understanding the therapeutic potential of the CB cell niche.

Growth Factors in the Carotid Body-An Update

The carotid body may undergo plasticity changes during development/ageing and in response to environmental (hypoxia and hyperoxia), metabolic, and inflammatory stimuli. The different cell types of the carotid body express a wide series of growth factors and corresponding receptors, which play a role in the modulation of carotid body function and plasticity. In particular, type I cells express nerve growth factor, brain-derived neurotrophic factor, neurotrophin 3, glial cell line-derived neurotrophic factor, ciliary neurotrophic factor, insulin-like-growth factor-I and -II, basic fibroblast growth factor, epidermal growth factor, transforming growth factor-α and -β, interleukin-1β and -6, tumor necrosis factor-α, vascular endothelial growth factor, and endothelin-1. Many specific growth factor receptors have been identified in type I cells, indicating autocrine/paracrine effects. Type II cells may also produce growth factors and express corresponding receptors. Future research will have to consider growth factors in further experimental models of cardiovascular, metabolic, and inflammatory diseases and in human (normal and pathologic) samples. From a methodological point of view, microarray and/or proteomic approaches would permit contemporary analyses of large groups of growth factors. The eventual identification of physical interactions between receptors of different growth factors and/or neuromodulators could also add insights regarding functional interactions between different trophic mechanisms.

Chronic hypoxia changes gene expression profile of primary rat carotid body cells: consequences on the expression of NOS isoforms and ET-1 receptors

Sustained chronic hypoxia (CH) produces morphological and functional changes in the carotid body (CB). Nitric oxide (NO) and endothelin-1 (ET-1) play a major role as modulators of the CB oxygen chemosensory process. To characterize the effects of CH related to normoxia (Nx) on gene expression, particularly on ET-1 and NO pathways, primary cultures of rat CB cells were exposed to 7 days of CH. Total RNA was extracted, and cDNA-32P was synthesized and hybridized with 1,185 genes printed on a nylon membrane Atlas cDNA Expression Array. Out of 324 differentially expressed genes, 184 genes were upregulated, while 140 genes were downregulated. The cluster annotation and protein network analyses showed that both NO and ET-1 signaling pathways were significantly enriched and key elements of each pathway were differentially expressed. Thus, we assessed the effect of CH at the protein level of nitric oxide synthase (NOS) isoforms and ET-1 receptors. CH induced an increase in the expression of endothelial NOS, inducible NOS, and ETB. During CH, the administration of SNAP, a NO donor, upregulated ETB. Treatment with Tezosentan (ET-1 receptor blocker) during CH upregulated all three NOS isoforms, while the NOS blocker L-NAME induced upregulation of iNOS and ETB and downregulated the protein levels of ETA. These results show that CH for 7 days changed the cultured cell CB gene expression profile, the NO and ET-1 signaling pathways were highly enriched, and these two signaling pathways interfered with the protein expression of each other.

Prenatal diagnosis of sex chromosome mosaicism with two marker chromosomes in three cell lines and a review of the literature

The present study described the diagnosis of a fetus with sex chromosome mosaicism in three cell lines and two marker chromosomes. A 24‑year‑old woman underwent amniocentesis at 21 weeks and 4 days of gestation due to noninvasive prenatal testing identifying that the fetus had sex chromosome abnormalities. Amniotic cell culture revealed a karyotype of 45,X[13]/46,X,+mar1[6]/46,X,+mar2[9], and prenatal ultrasound was unremarkable. The woman underwent repeat amniocentesis at 23 weeks and 4 days of gestation for molecular detection. Single nucleotide polymorphism (SNP) microarray analysis on uncultured amniocytes revealed that the fetus had two Y chromosomes and 7.8‑Mb deletions in Yq11.222q12. The deletion regions included DAZ, RBMY and PRY genes, which could cause spermatogenesis obstacle and sterility. Interphase fluorescence in situ hybridization (FISH) using centromeric probes DXZ1/DYZ3/D18Z1 was performed on uncultured amniocytes to verify the two marker chromosomes to be Y chromosome derivatives. According to these examinations, the mar1 was identified as a derivative of the Y chromosome with a deletion in Yq11.222q12, and the mar2 was identified as a dicentric derivative of the Y chromosome. The molecular karyotype was therefore 45,X,ish(DXZ1+, DYZ3‑,D18Z1++)[5]/46,X,del(Y)(q11.222),ish(DXZ1+,DYZ3+,D18Z1++)[11]/46, X,idic(Y)(q11.222),ish(DXZ1+,DYZ3++,D18Z1++)[14]. The comprehensive use of cytogenetic, SNP array and FISH detections was advantageous for accurately identifying the karyotype, identifying the origin of the marker chromosome and preparing effective genetic counseling.

Peripheral chemoreceptors: function and plasticity of the carotid body

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.

Divergent postnatal development of the carotid body in DBA/2J and A/J strains of mice

We have previously shown that the adult DBA/2J and A/J strains of mice differ in carotid body volume and morphology. The question has arisen whether these differences develop during the prenatal or postnatal period. Investigating morphological development of the carotid body and contributing genes in these mice can provide further understanding of the appropriate formation of the carotid body. We examined the carotid body of these mice from 1 day to 4 wk old for differences in volume, morphology, and gene expression of Gdnf family, Dlx2, Msx2, and Phox2b. The two strains showed divergent morphology starting at 1 wk old. The volume of the carotid body increased from 1 wk up to 2 wk old to the level of 4 wk old in the DBA/2J mice but not in the A/J mice. This corresponds with immunoreactivity of LC3, an autophagy marker, in A/J tissues at 10 days and 2 wk. The differences in gene expression were examined at 1 wk, 10 days, and 2 wk old, because divergent growth occurred during this period. The DBA/2J's carotid body at 1 wk old showed a greater expression of Msx2 than the A/J's carotid body. No other candidate genes showed consistent differences between the ages and strains. The difference was not seen in sympathetic cervical ganglia of 1 wk old, suggesting that the difference is carotid body specific. The current study indicates the critical postnatal period for developing distinctive morphology of the carotid body in these mice. Further studies are required to further elucidate a role of Msx2 and other uninvestigated genes.

Trophic factors in the carotid body

The aim of the present study is to provide a review of the expression and action of trophic factors in the carotid body. In glomic type I cells, the following factors have been identified: brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, artemin, ciliary neurotrophic factor, insulin-like growth factors-I and -II, basic fibroblast growth factor, epidermal growth factor, transforming growth factor-alpha and -beta1, interleukin-1beta and -6, tumour necrosis factor-alpha, vascular endothelial growth factor, and endothelin-1 (ET-1). Growth factor receptors in the above cells include p75LNGFR, TrkA, TrkB, RET, GDNF family receptors alpha1-3, gp130, IL-6Ralpha, EGFR, FGFR1, IL1-RI, TNF-RI, VEGFR-1 and -2, ETA and ETB receptors, and PDGFR-alpha. Differential local expression of growth factors and corresponding receptors plays a role in pre- and postnatal development of the carotid body. Their local actions contribute toward producing the morphologic and molecular changes associated with chronic hypoxia and/or hypertension, such as cellular hyperplasia, extracellular matrix expansion, changes in channel densities, and neurotransmitter patterns. Neurotrophic factor production is also considered to play a key role in the therapeutic effects of intracerebral carotid body grafts in Parkinson's disease. Future research should also focus on trophic actions on carotid body type I cells by peptide neuromodulators, which are known to be present in the carotid body and to show trophic effects on other cell populations, that is, angiotensin II, adrenomedullin, bombesin, calcitonin, calcitonin gene-related peptide, cholecystokinin, erythropoietin, galanin, opioids, pituitary adenylate cyclase-activating polypeptide, atrial natriuretic peptide, somatostatin, tachykinins, neuropeptide Y, neurotensin, and vasoactive intestinal peptide.

Postnatal growth of the carotid body

The size of the carotid body (CB) is increased significantly during the postnatal period. Type I cells in the CB are the chemoreceptive element and possess many neuron-like characteristics. In contrast to previous opinions that the number of type I cells is determined before birth, we have found that type I cells continue to proliferate over a period of at least 1 month after birth in rats. The proliferation of type I cells is influenced by oxygen concentration in ambient air. Specifically, hyperoxia inhibits the type I cell proliferation, resulting in small CBs throughout life and the permanent impairment of CB chemoreception. On the other hand, hypoxia enhances the type I cell proliferation. Whether hypoxia causes long-lasting effects on CB morphology and function remains to be determined. Besides type I cell proliferation, other cellular components in the CB undergo proliferation and growth as well. In the nearby petrosal ganglion and superior cervical ganglion, both involved in CB chemoreception, cellular proliferation is limited to glial cells and no proliferation of neurons is observed. Also, expression of neurotrophic factors, particularly, BDNF and GDNF, is observed in type I cells of neonatal rats. Taken together, the CB undergoes significant morphological and functional changes during the postnatal period over at least 1 month. This process can be altered by oxygen concentration in ambient air.

Expression and function of GDNF family ligands and receptors in the carotid body

The carotid body is a neural crest-derived neuroendocrine organ that detects the oxygen level in blood and regulates ventilation. Unlike many other neural crest derivatives, the trophic factors mediating survival and differentiation of neuroendocrine cells of the carotid body are unknown. Given that many neural crest derivatives rely on the glial cell line-derived neurotrophic factor (GDNF) family of ligands (GFLs) for survival and function, we undertook an analysis of the carotid body as a potential site of GFL action. RET and GDNF family receptor alphas (GFRalpha) 1-3 are expressed in the developing carotid body as detected by RT-PCR and immunocytochemistry. mRNA for GDNF, and artemin (ARTN) were also present. In vitro, treatment with GDNF, neurturin (NRTN), or ARTN, individually or in combination, produced an increase in the number and length of processes of the Type-I glomus cells of the carotid body [embryonic day-17 (E17) rats]. However, GFLs alone or in combination had no effect on glomus cell survival in either postnatal day-1 (P1) or E17 carotid body cultures. These results suggest that one or more GFLs may have a role in carotid body function. In addition, the results of this study suggest that endogenous or exogenous GFLs may enhance target innervation by carotid body transplants.

Carotid body chemoreceptors in dissociated cell culture

Carotid body (CB) glomus or type 1 cells act as peripheral chemoreceptors which detect changes in arterial PO(2), PCO(2), and pH and help maintain homeostasis via the reflex control of ventilation. Over the last approximately 12 years significant progress has been made towards understanding chemotransduction mechanisms using freshly isolated or cultured type 1 cells. The latter preparation allows several powerful experimental manipulations (e.g., co-culture with sensory neurons) resulting in significant advances in our understanding of CB chemoreception. Here, we review several properties of type 1 cells after several days to weeks in culture. Typically, cultured type 1 cells grow in monolayer clusters enveloped by glial-like, type II, or sustentacular cells, which are immunopositive for the glial marker, glial fibrillary acid protein (GFAP). These cells can undergo DNA synthesis, evidenced by uptake of bromodeoxyuridine (BrdU), and show a limited capacity for cell division. Mitosis and survival of type 1 cells can be regulated by oxygen tension and/or growth factors (e.g., bFGF, insulin). In the rat, type 1 cells are immunopositive for several monoaminergic markers, including tyrosine hydroxylase (TH), dopamine transporter (DAT), and 5-HT. They also express cholinergic markers (e.g., vesicular acetylcholine transporter; VAChT), the highly conserved synaptic vesicle protein (SV2), and gap junctional proteins including Connexin 32 (Cx32). Moreover, in long-term culture ( approximately 2 weeks) they retain expression of O(2)-sensitive, TASK-1-like, and Ca(2+)-dependent (BK), K(+) channels as revealed by immunocytochemistry or RT-PCR analysis of mRNA extracted from type 1 clusters after removal from the culture surface.

Chemoafferent degeneration and carotid body hypoplasia following chronic hyperoxia in newborn rats

1. To define the role of environmental oxygen in regulating postnatal maturation of the carotid body afferent pathway, light and electron microscopic methods were used to compare chemoafferent neurone survival and carotid body development in newborn rats reared from birth in normoxia (21 % O2) or chronic hyperoxia (60 % O2). 2. Four weeks of chronic hyperoxia resulted in a significant 41 % decrease in the number of unmyelinated axons in the carotid sinus nerve, compared with age-matched normoxic controls. In contrast, the number of myelinated axons was unaffected by hyperoxic exposure. 3. Chemoafferent neurones, located in the glossopharyngeal petrosal ganglion, already exhibited degenerative changes following 1 week of hyperoxia from birth, indicating that even a relatively short hyperoxic exposure was sufficient to derange normal chemoafferent development. In contrast, no such changes were observed in the vagal nodose ganglion, demonstrating that the effect of high oxygen levels was specific to sensory neurones in the carotid body afferent pathway. Moreover, petrosal ganglion neurones were sensitive to hyperoxic exposure only during the early postnatal period. 4. Chemoafferent degeneration in chronically hyperoxic animals was accompanied by marked hypoplasia of the carotid body. In view of previous findings from our laboratory that chemoafferent neurones require trophic support from the carotid body for survival after birth, we propose that chemoafferent degeneration following chronic hyperoxia is due specifically to the loss of target tissue in the carotid body.

Role of basic FGF and oxygen in control of proliferation, survival, and neuronal differentiation in carotid body chromaffin cells

Crest-derived glomus cells of the carotid body (CB) are O(2)-sensitive chemoreceptors, which resemble sympathoadrenal (SA) chromaffin cells. In this study, we tested whether perinatal rat glomus cells are sensitive to basic fibroblast growth factor (bFGF) in vitro and whether their sensitivity is regulated by oxygen. In chemically defined medium, bFGF (1-100 ng/ml) caused a significant, dose-dependent increase in the number of surviving tyrosine hydroxylase-positive (TH+) glomus cells in embryonic (E17-E19) CB cultures, following a 48-hr exposure. Though basic FGF (10 ng/ml) appeared mitogenic for these cells, based on stimulation of bromodeoxyuridine (BrdU) uptake, it supported survival of only approximately 60% of the initial TH+ population, suggesting that significant cell death was occurring. This apparent cell loss in E17 cultures could be largely prevented by combined treatment with bFGF and low oxygen (6% O(2)). In contrast, in early postnatal (P1) cultures, glomus cell number was relatively unchanged over 48 hr under control conditions or in presence of mitogenic activity from either bFGF or low oxygen. However, combined treatment with both bFGF and low oxygen stimulated proliferation of P1 glomus cells such that by 48 hr the TH+ population had increased to approximately 1.5x the initial density. Basic FGF (10 ng/ ml) also stimulated neurite outgrowth and neurofilament expression in E18-E19, but not P1-P3, glomus cells. In contrast to bFGF, treatment with nerve growth factor was ineffective. Taken together, these results suggest that bFGF and low oxygen are mitogens for perinatal CB chromaffin cells and interact cooperatively as survival factors. It is plausible that these mechanisms may operate to regulate chemoreceptor cell density, during the animal's transition from in utero (hypoxic) to ex utero (normoxic)life.

Basic fibroblast growth factor regulates ionic currents and excitability of fetal rat carotid body chemoreceptors

Basic fibroblast growth factor (bFGF) and nerve growth factor (NGF) are known mitogens and/or differentiation factors for cells of the sympathoadrenal lineage. Though carotid body (CB) chemoreceptors (type 1 cells) are considered part of this lineage, their response to bFGF is unknown and so far they appear unresponsive to NGF in vitro. In this study we use whole-cell recording to investigate whether bFGF (and NGF) can influence the development of ionic currents in these chemoreceptors, cultured from fetal (E18-19) rat pups. bFGF (10ng/ml) significantly augmented both transient inward Na+ and outward K+ currents in type 1 cells after only 2 days of treatment; after normalizing for the accompanying increase in cell size, as indicated by whole-cell capacitance, the Na+ current density was nonetheless increased by bFGF. Unlike controls, bFGF-treated type 1 cells readily fired action potentials following depolarization. These effects were not mimicked by NGF (100 ng/ml) treatment. Since the carotid body is one of the most richly vascularized organs and bFGF is a potent angiogenic factor, it is conceivable that variations in local bFGF concentrations during fetal development may contribute to the known species differences in CB chemoreceptor excitability.

Effects of hypoxia on the intracellular K+ of clustered and isolated glomus cells of mice and rats

Carotid bodies of rats and mice were used to measure the intracellular potassium activity, ai(K), of clustered and isolated glomus cells normally oxygenated (pO2 102-139 Torr), and during hypoxia (pO2 2-82 Torr) induced by Na-dithionite. ai(K) was measured with intracellular ion-selective microelectrodes, and the resting potential (EM) with KCl-filled micropipettes. Under normoxia, the ai(K) of clustered cells in both species was higher than that of isolated cells. This resulted in more negative potassium equilibrium potentials (EK's). There was no correlation between ai(K) and EM in clustered cells, but this correlation was significant in isolated cells. Hypoxia significantly decreased ai(K) in clustered and single mouse cells, and in clustered rat cells, although its effects on single rat cells were variable. ai(K) decreases were accompanied by cell depolarization and positive shifts in EK. During hypoxia, there were significant correlations between ai(K) and EM in all cells. It is suggested that ai(K) did not influence the EM of clustered cells under normoxia because of interference by K+ pumping mechanisms toward glomus cells from surrounding sustentacular processes. This hindrance is not present when glomus cells are isolated. During hypoxia K+ pumping from sustentacular cells is disrupted, allowing the EM of clustered glomus cells to follow their ai(K) and behave like isolated cells. The different effects of hypoxia on isolated rat and mouse cells may be due to activation of different types of glomus cells.

Electrical coupling between cultured glomus cells of the rat carotid body: observations with current and voltage clamping

Electrically coupled pairs of cultured rat glomus cells were used. In one group of experiments, both cells were current-clamped. Delivery of positive or negative pulses to Cell 1 elicited appreciable voltage noise in this cell and large action potentials (probably Ca2+ spikes) in about 10% of them. Both passive and active electrical events spread to Cell 2, presumably through the gap junctions between them. The coupling coefficient (Kc) was larger for the spikes than for non-regenerative voltage noise. In another group of experiments, Cell 1 was current-clamped and Cell 2 was voltage-clamped at Cell 1 EM. Pulses of either polarity, delivered to Cell 1, produced current flow through the intercellular junction and allowed direct measurements of junctional currents (Ij) and total conductances (Gj). Ij had a mean value of about 12.5 pA and Gj of 391 pS. Unitary (presumably single channel) conductance (gj) was about 78 pS.

Culture of arterial chemoreceptor cells from adult cats in defined medium

Recently patch clamp techniques and optical fluorometric techniques have been applied to freshly dissociated or cultured carotid body. However, very few studies have shown the effects of the dissociation and/or culture conditions on the health and function of the cells. The purpose of this study was to develop a culture method which support healthy and functioning carotid body cells from adult cats. Carotid bodies were dissociated with 0.1-0.2% collagenase and gentle trituration. The cells were plated on glass wells coated with poly-D-lysin and Matrigel, and cultured in chemically defined medium. Culture was maintained for up to 37 days without overgrowth of fibroblasts. Glomus cells extended their processes within and from clusters. Single glomus cells acquired the shape of neurons. Glomus cells synthesized dopamine and its secretion increased during exposure of the cells to hypoxia. Tyrosine hydroxylase was expressed throughout the culture period. These results indicate that glomus cells cultured under conditions described here are healthy and function in a manner similar to that in vivo.

Whole-cell and perforated-patch recordings from O2-sensitive rat carotid body cells grown in short- and long-term culture

We are investigating transduction mechanisms in a major peripheral chemosensory organ, the rat carotid body, using short- and long-term dissociated cell cultures and patch-clamp, whole-cell recording. In this study membrane properties of cultured glomus or type I cells were characterized with conventional whole-cell recording and the new perforated-patch technique during control (160 Torr) and low-PO2 (20 Torr) conditions. These cells contained voltage-gated channels typical of electrically excitable cells and had large input resistances (approx. 2 G omega). Under whole-cell voltage clamp the cells produced brief inactivating inward currents, which were largely abolished by 0.2-2.0 microM tetrodotoxin, followed by prolonged outward currents, which were reduced by 5 mM tetraethylammonium or abolished by the substitution of Cs+ ions for K+ ions in the pipette. On exposure to hypoxia the outward K+ current was reduced typically by 15%-20% with both conventional whole-cell and perforated-patch recording, which minimizes washout of the cell's cytoplasm. This effect persisted in long-term culture and was specific, since the inward current was unaffected and, moreover, it did not occur in cultured small intensely fluorescent cells, which are closely related to glomus cells. These properties of cultured rat glomus cells are contrasted with those recently reported for freshly isolated rabbit glomus cells.

Electrophysiological evidence for the reconstitution of chemosensory units in co-cultures of carotid body and nodose ganglion neurons

The electrophysiological characteristics of nodose ganglion sensory neurons, cultured alone or co-cultured with carotid body tissue, were compared. Some properties of the neurons and their response to acid (a carotid body 'natural' stimulus) changed in the presence of this tissue. (a) The evoked action potential after-hyperpolarization was smaller and longer whereas spike amplitude and duration, and the passive membrane properties remained unaltered. (b) Spontaneously occurring action potentials happened more frequently (16% vs 3%). (c) Acid solutions induced appreciable depolarization, an increased discharge, or both, only in a population of co-cultured neurons. These changes probably arose because of synaptic and/or trophic interactions between neurons and glomus cells.

Carbonic anhydrase and neuronal enzymes in cultured glomus cells of the carotid body of the rat

The cellular localization of carbonic anhydrase (CAH) in the carotid body of the rat was investigated by means of Hansson's cobalt-precipitation technique in cultures of dissociated cells. In both young (2-day-old) and old (77-day-old) cultures, the parenchymal glomus (type-I) cells were selectively stained by this technique, and in addition expressed tyrosine hydroxylase and neuron-specific enolase as revealed by immunofluorescence. Enzymic reaction product of CAH appeared to be predominantly intracellular since staining was more intense and occurred more rapidly following permeabilization of the cell membranes with Triton X-100; its formation was inhibited by the CAH-inhibitor acetazolamide (1-10 microM) or by increasing the pH from 5.8 to 7.5. Cryostat sections of the carotid bifurcation revealed intense CAH-reaction product in cell clusters of the carotid body, in a few cells of the nodose ganglion, and in red blood cells. Neuronal cell bodies of the petrosal ganglion and superior cervical ganglion (SCG) were largely non-reactive. The SCG is known to contain clusters of small intensely fluorescent (SIF) cells, which were also non-reactive when grown in dissociated cell culture. Thus, although glomus and SIF cells are often considered to be similar cell types, functional CAH-activity appears unique to glomus cells, and this may be important for the physiological response of the carotid body to certain chemosensory stimuli.

Localization of acetylcholinesterase in dissociated cell cultures of the carotid body of the rat

The localization of acetylcholinesterase (AChE) was investigated at the cellular and subcellular levels in dissociated cell cultures of the carotid body of the neonatal rat, prepared by the methods of Fishman and Schaffner (1984). In the presence of iso-OMPA, which blocks nonspecific cholinesterase, staining was confined almost exclusively to glomus-cell clusters and occasional isolated cells. These clusters grow as discrete islands scattered throughout the culture and display typical catecholamine (CA) fluorescence as in vivo. AChE staining was abolished or reduced by the cholinesterase inhibitors eserine (30-100 microM), or (the poorly lipid soluble) echothiophate (8 microM). Processing of the same culture sequentially for the demonstration of both AChE and CA revealed that glomus-cell clusters and individual glomus cells were consistently positive for both. In electron micrographs AChE reaction product was associated intracellularly with the nuclear envelope and cytoplasm of glomus cells (identified by their characteristic dense cored granules), as well as extracellularly with the boundaries of contiguous glomus cells. Significantly, reaction product occurred in some glomus cell profiles that had both dense-cored and clear (cholinergic-like) vesicles. These findings are discussed in the context of a possible dual (adrenergic/cholinergic) function status of glomus cells in the rat's carotid body.

A quantitative electron microscopic study of the effect of glucocorticoids in vivo on the early postnatal differentiation of paraneuronal cells in the carotid body and the adrenal medulla of the rat

The postnatal differentiation of carotid body chief cells and endocrine adrenal medullary cells was comparatively examined during ontogenesis and in rats which were treated with dexamethasone for 7 days after birth. Ultrastructure and innervation of carotid body chief cells are mature in neonates according to the functional requirements of chemoreception. By the end of the first postnatal week, only an increase in number of dense core vesicles can be noticed, the concentration of which then will reach the adult level. Under the effect of dexamethasone most of the heterochromatin is transformed into finely dispersed euchromatin within the nuclei of carotid body chief cells. In the cytoplasm, the Golgi apparatus becomes larger and the granular endoplasmic reticulum hypertrophic. The number of catecholamines storing dense core vesicles increases considerably. The innervation density remains constant. In contrast to the carotid body chief cells, the adrenal medullary cells have not reached their definitive maturity at the time of birth. Besides phenotypes of adrenaline-cells, noradrenaline-cells and small granules containing cells, pheochromoblasts and intermediary cells can be seen as well. Their cytoplasm is sparse, the concentration of dense core vesicles and the innervation density very low. After 8 days of postnatal ontogenesis, pheochromoblasts and intermediary cells are no longer present in the adrenal medulla. In adrenaline-cells and noradrenaline-cells, important processes of growth can be noticed, the cytoplasm has grown in extent, the number of dense core vesicles doubled and the innervation density of single cells triplicated. Only the few small granules containing cells remain small. Under the effect of dexamethasone also in the nuclei of chromaffin cells a transformation of heterochromatin into euchromatin occurs. The increase in number of dense core vesicles is relatively lower than in carotid body chief cells. The significant growth of innervation density during the first postnatal week was inhibited. Our observations suggest that dexamethasone stimulates the synthesis of catecholamines in adrenal medullary cells of newborn rats less pronouncedly than in carotid body chief cells. This could be attributed to the inhibited formation of synapses of growing chromaffin cells and to the in vivo active endocrine counter-regulation.

Oxygen chemoreception by carotid body cells in culture

Chemoreceptors for oxygen reside within the carotid body, but it is not known which cells actually sense hypoxia and by what mechanisms they transduce this information into afferent signals in the carotid sinus nerve. We have developed systems for the growth of glomus cells of the carotid body in dissociated cell culture. Here we demonstrate that, as in vivo, these cells contain the putative neurotransmitters dopamine, serotonin, and norepinephrine. Oxygen tension regulates the rate of dopamine secretion from the glomus cells. Similar to chemically stimulated catecholamine secretion from other adrenergic cells this hypoxia-stimulated release requires extracellular calcium. These results are compatible with the suggestion that the glomus cells of the carotid body are chemoreceptor cells and that they signal hypoxia by regulated secretion of dopamine.