The role of dihydropydine-sensitive Ca2 + channels in stimulus-evoked catecholamine release from chemoreceptor cells of the carotid body

Producción CientíficaAhatraet-The present study utilized an in vitro preparation of the rabbit carotid body, with tissue catecholamine stores labeled by incubation with ‘H-tyrosine. The goal was to characterize pharmacologically the vol~g~~n&nt Ca*+ channels present in the type I (glomus) cells of this arterial chemoreceptor organ, and to elucidate their role as pathways for Ca2+ entry. We found that release of ‘H-dopamine induced by high external potassium was over 95% dependent on external cakium concentration and that this release was 9&100% inhibited by the dihydropy~~ne antagonists, nisoldipine and nitrendipine, and was potentiated by the dihydropyridine agonist, BayK 8444. Therefore, any stimulus-induced, cakiumdependent release of 3H-dopamine that was inhibited by nisoldipine and potentiated by BayK 8644, was considered to be supported by Ca2+ entry into the cells via voltage-dependent Ca2+ channels. Significant differences were observed in the release of ‘H-dopamine induced by 75 vs 25mM K+. On prolonged stimulation, release induced by 75 mM K+ was large and transient, whilst that induced by 25 mM K+, although more moderate, was sustained. The release elicited by 75 mM K+ was inhibited approximately 90% by 1.5 mM Co2+ or 625 nM nisoldipine, while release by 25 mM K+ was completely blocked by 0.6 mM Co*+ or 125 nM nisoldipine. Low PO,-induced release of 3H-dopamine was 95% dependent on Ca*+, and was inhibited by nisoldipine (625 nM) in a manner inversely proportional to the intensity of hypoxic stimulation, i.e. 79% inhibition at a PO, of 49 Torr, and 20% inhibition at PO2 of 0 Torr. BayK 8644 potentiatcd the release induced by moderate hypoxic stimuli. Release elicited by high PCOJlow pH, or by Na+-propionate or dinitrophenol~n~ining solutions, was approximately 80% Ca’+-dependent, and the ~hyd~y~din~ failed to modify this release. It is concluded that type I mlls possess vol~~de~nd~t Ca ‘+ channels sensitive to the dihydropy~dines, which in agreement with previous el~trophysiolo~~l data should be defined as L-type Ca*+ channels. Calcium entry which supports the release of 3H-dopamine elicited by moderate hypoxia should occur mainly through these channels while the release induced by strong hypoxic stimuli will be SetNed by Ca2+ entry which occurs in part via voltage-dependent Ca2+ channels, and in part through an additional pathway, probably a Na+/Ca2+ exchanger. The insensitivity to dihydropyridines of the release of )H-dopamine induced by high 1DC02/low pH, Na+-propionate and dinitrophenol may indicate a complete loss of efficacy of the drugs to modulate Ca 2+ channels under these conditions or more likely, that other mechanisms are activated, probably the Na+-Ca’+ exchanger. Carotid body (CB) chemoreceptors are thought to be composite receptors in which the type I (glomus) cells detect changes in blood PO,, PCO, and pH and respond with the release of neurotransmitt~ to activate the closely apposed chemosensory nerve terminals.~** One such neurotransmitter that has received considerable attention in recent years and is known to be released by the type I cells is dopamine (DA). This biogenic amine has been shown to be released in proportion to both the intensity of stimulation and the resultant sensory discharge recorded from the carotid sinus nerve $To whom correspondence should be addressed. Abbr~~~~~~ CB, carotid body; CSN, carotid sinus nerve; DA, dopamine; DHMA, dihydrox~~delic acid, DOPAC, dihydroxyphenyl acetic acid; NE, norepinephrine. (CSN). This relationship between stimulu

Intracellular Ca2 + deposits and catecholamine secretion by chemoreceptor cells of the rabbit carotid body

Producción CientíficaThe pívotal role of íntracellular free [Ca2+] fluctuatíons in the control of cellular functíons such as contraction and secretíon, íncludíng the release of neurotransmítters, was recognized many decades ago (see Rubín, 1982). More recently, the list of cellular functíons tríggered or modulated by the levels of Ca2+¡ has grown enormously. Addítional functíons regulated by [Ca2+)¡ include neuronal excítabílity, synaptic plastícíty, gene ex­ pressíon, cellular metabolísm, cell dívísíon and dífferentíatíon, and programmed cell dead (Míller, 1991; Clapham, 1995). Parallelíng the growth in this líst of Ca2+-controlled func­ tíons, a multíplicity of cellular mechanísms aimed at maintaining resting free [Ca2+)¡ in the range of l 00 nM for most cells has been described, allowing increases in Ca2+¡ levels that are specific in their magnitude, time course and spatial distributíon, accordíng to the cell function activated (Toescu, 1995). Since Ca2+ cannot be metabolized, cells regulate theír cytoplasmic levels of free Ca2+ through numerous bínding proteíns and influx and efflux mechanisms (Fíg 1). Ca2+ ínflux to cell cytoplasm from the extracellular milieu occurs vía voltage or receptor operated channels or vía yet ill-defined capacítatíve pathways; the Na+/Ca 2+ exchanger can also produce in sorne círcumstances net ínflux of Ca2+ (Míller, 1991; Clapham, 1995). Ca2+ ef­ flux to the extracellular space occurs against electrochemical gradíents, and thereby the pumpíng out of Ca2+ is directly (Caz+ pump) or indirectly (Na+/Ca2+) coupled to the hy­ drolysis of ATP

Hydroxycobalamin reveals the involvement of hydrogen sulfide in the hypoxic responses of rat carotid body chemoreceptor cells

Producción CientíficaCarotid body (CB) chemoreceptor cells sense arterial blood PO2, generating a neurosecretory response proportional to the intensity of hypoxia. Hydrogen sulfide (H2S) is a physiological gaseous messenger that is proposed to act as an oxygen sensor in CBs, although this concept remains controversial. In the present study we have used the H2S scavenger and vitamin B12 analog hydroxycobalamin (Cbl) as a new tool to investigate the involvement of endogenous H2S in CB oxygen sensing. We observed that the slow-release sulfide donor GYY4137 elicited catecholamine release from isolated whole carotid bodies, and that Cbl prevented this response. Cbl also abolished the rise in [Ca2+]i evoked by 50 µM NaHS in enzymatically dispersed CB glomus cells. Moreover, Cbl markedly inhibited the catecholamine release and [Ca2+]i rise caused by hypoxia in isolated CBs and dispersed glomus cells, respectively, whereas it did not alter these responses when they were evoked by high [K+]e. The L-type Ca2+ channel blocker nifedipine slightly inhibited the rise in CB chemoreceptor cells [Ca2+]i elicited by sulfide, whilst causing a somewhat larger attenuation of the hypoxia-induced Ca2+ signal. We conclude that Cbl is a useful and specific tool for studying the function of H2S in cells. Based on its effects on the CB chemoreceptor cells we propose that endogenous H2S is an amplifier of the hypoxic transduction cascade which acts mainly by stimulating non-L-type Ca2+ channels.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project BFU2015-70616-R)Junta de Castilla y León (project VA106G18)Centro de Investigación Biomédica en Red de Enfermedades Respiratorias . Instituto de Salud Carlos III (project CIBER CB06/06/0050

Ca2 + Dynamics in chemoreceptor cells: an overview

Producción CientíficaThe carotid body (CB) was defined as a sensory organ by De Castro in 1928. Two years later, Heymanns and coworkers demostrated that the organ was sensitive to alterations in blood gases and pH, in such a way that a decrease in blood P02 or pH or an increase in blood PC02 produced activation of the CB and, reflexely, hyperventilation. De Castro postulated that glomus cells were the sensor structures and that they should release sorn substance to transmit the stimulus to the sensory nerve endings (De Castro, 1928). De Castro's point of view, was widely accepted, and therefore the CB was considered a secondary sensory receptor. As a consequence, the principal aims of many workers in the chemoreception field have been to define the nature of the sensing mechanims ( sensory transduction process ) and to identify the substances released by chern cells

Significance of ROS in oxygen sensing in cell systems with sensitivy to ohysiological hypoxia

Reactive oxygen species (ROS) are oxygen-containing molecular entities which are more potent and effective oxidizing agents than is molecular oxygen itself. With the exception of phagocytic cells, where ROS play an important physiological role in defense reactions, ROS have classically been considered undesirable byproducts of cell metabolism, existing several cellular mechanisms aimed to dispose them. Recently, however, ROS have been considered important intracellular signaling molecules, which may act as mediators or second messengers in many cell functions. This is the proposed role for ROS in oxygen sensing in systems, such as carotid body chemoreceptor cells, pulmonary artery smooth muscle cells, and erythropoietin-producing cells. These unique cells comprise essential parts of homeostatic loops directed to maintain oxygen levels in multicellular organisms in situations of hypoxia. The present article examines the possible significance of ROS in these three cell systems, and proposes a set of criteria that ROS should satisfy for their consideration as mediators in hypoxic transduction cascades. In none of the three cell types do ROS satisfy these criteria, and thus it appears that alternative mechanisms are responsible for the transduction cascades linking hypoxia to the release of neurotransmitters in chemoreceptor cells, contraction in pulmonary artery smooth muscle cells and erythropoietin secretion in erythropoietin producing cells

Hypoxic pulmonary vasoconstriction, carotid body function and erythropoietin production in adult rats perinatally exposed to hyperoxia

Adult mammalians possess three cell systems that are activated by acute bodily hypoxia: pulmonary artery smooth muscle cells (PASMC), carotid body chemoreceptor cells (CBCC) and erythropoietin (EPO)-producing cells. In rats, chronic perinatal hyperoxia causes permanent carotid body (CB) atrophy and functional alterations of surviving CBCC. There are no studies on PASMC or EPO-producing cells. Our aim is to define possible long-lasting functional changes in PASMC or EPO-producing cells (measured as EPO plasma levels) and, further, to analyse CBCC functional alterations. We used 3- to 4-month-old rats born and reared in a normal atmosphere or exposed to perinatal hyperoxia (55–60% O2 for the last 5–6 days of pregnancy and 4 weeks after birth). Perinatal hyperoxia causes an almost complete loss of hypoxic pulmonary vasoconstriction (HPV), which was correlated with lung oxidative status in early postnatal life and prevented by antioxidant supplementation in the diet. O2-sensitivity of K+ currents in the PASMC of hyperoxic animals is normal, indicating that their inhibition is not sufficient to trigger HPV. Perinatal hyperoxia also abrogated responses elicited by hypoxia on catecholamine and cAMP metabolism in the CB. An increase in EPO plasma levels elicited by hypoxia was identical in hyperoxic and control animals, implying a normal functioning of EPO-producing cells. The loss of HPV observed in adult rats and caused by perinatal hyperoxia, comparable to oxygen therapy in premature infants, might represent a previously unrecognized complication of such a medical intervention capable of aggravating medical conditions such as regional pneumonias, atelectases or general anaesthesia in adult life.This work was supported by Grants BFU2012-37459 from the Ministry of Economy and Competitiveness (Spain) and Grant CIBER CB06/06/0050 from the Institute of Health Carlos III (Spain) to C. G. Also supported by Grants SAF2011-28150 to F.P-V and SAF2010-22066-C02-02 to AC from the Ministry of Economy and Competitiveness (Spain).Peer Reviewe

Analysis of Bone Histomorphometry in Rat and Guinea Pig Animal Models Subject to Hypoxia

Hypoxia may be associated with alterations in bone remodeling, but the published results are contradictory. The aim of this study was to characterize the bone morphometry changes subject to hypoxia for a better understanding of the bone response to hypoxia and its possible clinical consequences on the bone metabolism. This study analyzed the bone morphometry parameters by micro-computed tomography (?CT) in rat and guinea pig normobaric hypoxia models. Adult male and female Wistar rats were exposed to chronic hypoxia for 7 and 15 days. Additionally, adult male guinea pigs were exposed to chronic hypoxia for 15 days. The results showed that rats exposed to chronic constant and intermittent hypoxic conditions had a worse trabecular and cortical bone health than control rats (under a normoxic condition). Rats under chronic constant hypoxia were associated with a more deteriorated cortical tibia thickness, trabecular femur and tibia bone volume over the total volume (BV/TV), tibia trabecular number (Tb.N), and trabecular femur and tibia bone mineral density (BMD). In the case of chronic intermittent hypoxia, rats subjected to intermittent hypoxia had a lower cortical femur tissue mineral density (TMD), lower trabecular tibia BV/TV, and lower trabecular thickness (Tb.Th) of the tibia and lower tibia Tb.N. The results also showed that obese rats under a hypoxic condition had worse values for the femur and tibia BV/TV, tibia trabecular separation (Tb.Sp), femur and tibia Tb.N, and BMD for the femur and tibia than normoweight rats under a hypoxic condition. In conclusion, hypoxia and obesity may modify bone remodeling, and thus bone microarchitecture, and they might lead to reductions in the bone strength and therefore increase the risk of fragility fracture.Funding: The present study was supported by grant reference BFU2015-70616-R from MINECOFEDER (Spain Government) and Programa Estratégico IBGM, Escalera de Excelencia, Ref. CCVC8485, Consejería de Educacion, JCyL (Spain)

Effects of Gestational Intermittent Hypoxia on Placental Morphology and Fetal Development in a Murine Model of Sleep Apnea

Obstructive sleep apnea (OSA) during pregnancy is characterized by episodes of intermittent hypoxia (IH) during sleep, resulting in adverse health outcomes for mother and offspring. Despite a prevalence of 8-20% in pregnant women, this disorder is often underdiagnosed.We have developed a murine model of gestational OSA to study IH effects on pregnant mothers, placentas, fetuses, and offspring. One group of pregnant rats was exposed to IH during the last 2 weeks of gestation (GIH). One day before the delivery date, a cesarean section was performed. Other group of pregnant rats was allowed to give birth at term to study offspring's evolution.Preliminary results showed no significant weight differences in mothers and fetuses. However, the weight of GIH male offspring was significantly lower than the controls at 14 days (p < 0.01). The morphological study of the placentas showed an increase in fetal capillary branching, expansion of maternal blood spaces, and number of cells of the external trophectoderm in the tissues from GIH-exposed mothers. Additionally, the placentas from the experimental males were enlarged (p < 0.05). Further studies are needed to follow the long-term evolution of these changes to relate the histological findings of the placentas with functional development of the offspring in adulthood.Ayudas para la realización de proyectos de investigación UVa 2021 (PROYEMER 57-E.O.

Adaptación de asignaturas seleccionadas de la titulación de Logopedia a créditos ETCS. Implicaciones del alumnado

Producción CientíficaSe presenta una primera experiencia práctica en el marco del proceso de Convergencia Europea de la enseñanza. El proyecto nace con el objetivo de adaptar asignaturas seleccionadas del actual plan de estudios de la Titulación (Diplomatura) de Logopedia al reciente “Sistema de Transferencia de Créditos Europeos” (créditos ECTS o European Credit Transfer System). Con este fin se crea una red de carácter nacional en la que participan la Universidad de Valladolid, Salamanca y Castilla-La Mancha. En la presente comunicación se explican de forma exhaustiva diversos aspectos relacionados con la elaboración del proyecto: selección de asignaturas, implicación de profesorado y alumnado, así como la programación de actividades y acciones que se están llevando a cabo actualmente

Chemoreception in the context of the general biology of ROS

Producción CientíficaSuperoxide anion is the most important reactive oxygen species (ROS) primarily generated in cells. The main cellular constituents with capabilities to generate superoxide anion areNADPHoxidases and mitochondrial respiratory chain. The emphasis of our article is centered in critically examining hypotheses proposing that ROS generated by NADPH oxidase and mitochondria are key elements in O2-sensing and hypoxic responses generation in carotid body chemoreceptor cells. Available data indicate that chemoreceptor cells express a specific isoform of NADPH oxidase that is activated by hypoxia; generated ROS acting as negative modulators of the carotid body (CB) hypoxic responses. Literature is also consistent in supporting that poisoned respiratory chain can produce high amounts of ROS, making mitochondrial ROS potential triggers-modulators of the CB activation elicited by mitochondrial venoms. However, most data favour the notion that levels of hypoxia, capable of strongly activating chemoreceptor cells, would not increase the rate of ROS production in mitochondria, making mitochondrial ROS unlikely triggers of hypoxic responses in the CB. Finally, we review recent literature on heme oxygenases from two perspectives, as potential O2-sensors in chemoreceptor cells and as generators of bilirubin which is considered to be a ROS scavenger of major quantitative importance in mammalian cells