Search

Transient receptor potential melastatin 4 (TRPM4) is a voltage-dependent, nonselective cation channel. Under pathological conditions, sustained activation of TRPM4 leads to oncotic cell death. Here, we report the upregulation of TRPM4 in vascular endothelium following hypoxia/ischemia in vitro and in vivo. In human umbilical vein endothelial cells, TRPM4 expression was increased at both the mRNA and protein levels following oxygen-glucose deprivation. Blocking TRPM4 with 9-phenanthrol greatly enhanced tube formation on Matrigel. In a rat permanent middle cerebral artery occlusion model, TRPM4 was upregulated in the vascular endothelium within the penumbra region after stroke. TRPM4 expression peaked 1 day post-occlusion and gradually decreased. In vivo siRNA-mediated TRPM4 silencing enhanced angiogenesis and improved capillary integrity. A twofold reduction in infarct volume and a substantial recovery of motor function were observed in animals receiving the siRNA treatment. Interestingly, the protective effect of TRPM4 suppression disappeared 5 days after stroke induction, indicating that TRPM4 upregulation is critical for cerebral damage during the acute phase of stroke. TRPM4 could be a potential therapeutic target for ischemic stroke. [ABSTRACT FROM AUTHOR]

Both hypoxia and carbon dioxide increase cerebral blood flow (CBF), and their effective interaction is currently thought to be additive. Our objective was to test this hypothesis. Eight healthy subjects breathed a series of progressively hypoxic gases at three levels of carbon dioxide. Middle cerebral artery velocity, as an index of CBF; partial pressures of carbon dioxide and oxygen and concentration of oxygen in arterial blood; and mean arterial blood pressure were monitored. The product of middle cerebral artery velocity and arterial concentration of oxygen was used as an index of cerebral oxygen delivery. Two-way repeated measures analyses of variance (rmANOVA) found a significant interaction of carbon dioxide and hypoxia factors for both CBF and cerebral oxygen delivery. Regression models using sigmoidal dependence on carbon dioxide and a rectangular hyperbolic dependence on hypoxia were fitted to the data to illustrate this interaction. We concluded that carbon dioxide and hypoxia act synergistically in their control of CBF so that the delivery of oxygen to the brain is enhanced during hypoxic hypercapnia and, although reduced during normoxic hypocapnia, can be restored to normal levels with progressive hypoxia. [ABSTRACT FROM AUTHOR]

Erythropoietin (Epo)-induced polycythemia is the main factor of adaptation to hypoxia. In this study, we analysed the effects of Epo deficiency on intrinsic functional properties of slow and fast twitch muscles in a model of erythropoietin deficient mice (Epo-TAgh) exposed to hypoxia. We hypothesised that Epo deficiency would be deleterious for skeletal muscle structure and phenotype, which could change its functional properties and alters the adaptive response to ambient hypoxia. Wild-type (WT) and Epo-TAgh mice were left in hypobaric chamber at 420 mm Hg pressure for 14 days. Soleus (SOL) and extensor digitorum longus (EDL) were analysed in vitro by mechanical measurements, immunohistological and biochemical analyses. The results were compared to those obtained in corresponding muscles of age-matched normoxic groups. Our data did not show any difference between the groups whatever the Epo deficiency and/or hypoxic conditions for twitch force, tetanic force, fatigue, typology and myosin heavy chain composition. Normoxic Epo-TAgh mice exhibit improved capillary-to-fibre ratio compared to WT mice in both SOL and EDL whereas no angiogenic effects of hypoxia or combined Epo-deficency/hypoxia were observed. These results suggest that skeletal muscles possess a great capacity of adaptation to Epo deficiency. Then Epo deficiency is not a sufficient factor to modify intrinsic functional properties of skeletal muscles. [ABSTRACT FROM AUTHOR]

The hypoxia-inducible factor (HIF)-1 is critically involved in the cellular adaptation to a decrease in oxygen availability. The influence of HIF-1α for the development of cardiac hypertrophy and cardiac function that occurs in response to sustained pressure overload has been mainly attributed to a challenged cardiac angiogenesis and cardiac hypertrophy up to now. Hif-1α+/+ and Hif-1α+/− mice were studied regarding left ventricular hypertrophy and cardiac function after being subjected to transverse aortic constriction (TAC). After TAC, both Hif-1α+/+ and Hif-1α+/− mice developed left ventricular hypertrophy with increased posterior wall thickness, septum thickness and increased left ventricular weight to a similar extent. No significant difference in cardiac vessel density was observed between Hif-1α+/+ and Hif-1α+/− mice. However, only the Hif-1α+/− mice developed severe heart failure as revealed by a significantly reduced fractional shortening mostly due to increased end-systolic left ventricular diameter. On the single cell level this correlated with reduced myocyte shortenings, decreased intracellular Ca2+-transients and SR-Ca2+ content in myocytes of Hif-1a+/− mice. Thus, HIF-1α can be critically involved in the preservation of cardiac function after chronic pressure overload without affecting cardiac hypertrophy. This effect is mediated via HIF-dependent modulation of cardiac calcium handling and contractility. [ABSTRACT FROM AUTHOR]

Articular chondrocytes experience low oxygen (O2) levels compared with many other tissues, and values fall further in disease states. Chondrocyte intracellular pH (pHi) is a powerful modulator of matrix synthesis and is principally regulated by Na+-H+ exchange (NHE). In equine chondrocytes, NHE is inhibited when cells are incubated for 3 h at low O2, leading to intracellular acidosis. O2-dependent changes in reactive oxygen species (ROS) levels appear to underlie this effect. The present study examines whether hypoxia can influence chondrocyte NHE activity and pHi over shorter timescales using the pH-sensitive fluoroprobe BCECF in cells isolated not only from equine cartilage but also from bovine tissue. O2 levels in initially oxygenated solutions gassed with N2 fell to approximately 1% within 2 h. A progressive fall in pHi and acid extrusion capacity was observed, with statistically significant effects ( P < 0.05) apparent within 3 h. For equine and bovine cell populations subjected to step change in O2 by resuspension in hypoxic (1%) solutions, a decline in acid extrusion and pHi was observed within 10 min and continued throughout the recording period. This effect represented inhibition of the NHE-mediated fraction of acid extrusion. Cells subjected to hypoxic solutions supplemented with CoCl2 (100 μM) or antimycin A (100 µM) to raise levels of ROS did not acidify. The conserved nature and rapidity of the response to hypoxia has considerable implications for chondrocyte homeostasis and potentially for the maintenance of cartilage integrity. [ABSTRACT FROM AUTHOR]

Cancer accounts for 13% of the yearly total mortality worldwide. Most cancer deaths are the sequel of metastatic diseases rather than of primary tumor growth. Thus, the major challenge in tumor therapy is the tumor cells’ ability to metastasize. The extent to which a tumor metastasizes correlates with the tumor cells’ migratory activity. Tumor cell migration requires a coordinated formation and release of cell adhesion contacts, a controlled cytoskeletal dynamics, the digestion and reorganization of the extracellular matrix, and local ion and water transport across the plasma membrane. All of these operations depend on intracellular pH (pHi) and extracellular pH (pHe). Numerous H+, HCO, and monocarboxylate transporters as well as different carbonic anhydrase isozymes have considerable impact on pHi and pHe which spotlights them as possible, potential targets for anticancer therapeutics. Especially in solid tumors whose vascularization is often not sufficient, tumor cells cope with hypoxia and the resulting glycolysis by overexpressing the Na+/H+ exchanger NHE1, monocarboxylate transporters MCT1 and/or MCT4, and the carbonic anhydrase CA IX. NHE1, MCT, and CA IX activity lead to an acidification of the extracellular space in order to maintain the cytosolic pH homeostasis stable. The present article gives a review on how this characteristic, acidic tumor micro- and nanoenvironment controls tumor cell migration. [ABSTRACT FROM AUTHOR]

Here, we describe novel mechanisms limiting a toxic cytosolic Ca2+ rise during adenosine 5′-triphosphate (ATP) depletion. We studied the effect of ATP depletion on Ca2+ signalling in mouse pancreatic acinar cells. Measurements of ATP in isolated cells after adenovirus-mediated expression of firefly luciferase revealed that the cytosolic ATP concentration fell from approximately 1 mM to near zero after treatment with oligomycin plus iodoacetate. ATP depletion resulted in the inhibition of Ca2+ extrusion, which was accompanied by a remarkably synchronous inhibition of store-operated Ca2+ influx. Alternative inhibition of Ca2+ extrusion by carboxyeosin had a much smaller effect on Ca2+ influx. The coordinated metabolic inhibition of Ca2+ influx and extrusion suggests the existence of a common ATP-dependent master regulator of both processes. ATP-depletion also suppressed acetylcholine (ACh)-induced Ca2+ oscillations, which was due to the inhibition of Ca2+ release from internal stores. This could be particularly important for limiting Ca2+ toxicity during periods of hypoxia. In contrast, metabolic control of Ca2+ influx and Ca2+ release from internal stores spectacularly failed to prevent large toxic Ca2+ responses induced by bile acids—activators of acute pancreatitis (a frequent and often fatal disease of the exocrine pancreas). The bile acids taurolithocholic acid 3-sulphate (TLC-S), taurochenodeoxycholic acid (TCDC) and taurocholic acid (TC) were used in our experiments. Neither Ca2+ release from internal stores nor Ca2+ influx triggered by bile acids were inhibited by ATP depletion, emphasising the danger of these pathological mechanisms. [ABSTRACT FROM AUTHOR]

The effect of hypoxia, induced by incubation under low (1%) oxygen tension or by exposure to CoCl2, on the expression and secretion of inflammation-related adipokines was examined in human adipocytes. Hypoxia led to a rapid and substantial increase (greater than sevenfold by 4 h of exposure to 1% O2) in the hypoxia-sensitive transcription factor, HIF-1α, in human adipocytes. This was accompanied by a major increase (up to 14-fold) in GLUT1 transporter mRNA level. Hypoxia (1% O2 or CoCl2) led to a reduction (up to threefold over 24 h) in adiponectin and haptoglobin mRNA levels; adiponectin secretion also decreased. No changes were observed in TNFα expression. In contrast, hypoxia resulted in substantial increases in FIAF/angiopoietin-like protein 4, IL-6, leptin, MIF, PAI-1 and vascular endothelial growth factor (VEGF) mRNA levels. The largest increases were with FIAF (maximum 210-fold), leptin (maximum 29-fold) and VEGF (maximum 23-fold); these were reversed on return to normoxia. The secretion of IL-6, leptin, MIF and VEGF from the adipocytes was also stimulated by exposure to 1% O2. These results demonstrate that hypoxia induces extensive changes in human adipocytes in the expression and release of inflammation-related adipokines. Hypoxia may underlie the development of the inflammatory response in adipocytes, leading to obesity-associated diseases. [ABSTRACT FROM AUTHOR]

Hypoxic brain cell injury is a complex process that results from a series of intracellular events. In this work, we tested whether severe hypoxia for 6 h can affect gene expression and protein levels of intracellular calcium channels, ryanodine receptors, and inositol 1,4,5-trisphosphate receptors in mouse cerebellum. In addition, we tested the effect of hypoxia on cerebellar granular cells of rats. We have found that gene expression of types 1 and 2 IP3 receptors is significantly increased after the exposure of mice to hypoxic stimulus for 6 h and also in rat cerebellar granular cells. Increased gene expression of IP3 receptors was reflected in increased protein levels of these channels as well. In this process, reactive oxygen species are most probably involved, as antioxidant quercetin abolished hypoxia-induced increase in both types 1 and 2 IP3 receptor. Ryanodine receptors of types 1 and 2 and sarco(endo)plasmic reticulum Ca2+-ATPase were not affected by hypoxia on the level of messenger RNA. To test physiological consequences, we measured levels of intracellular calcium. We observed significantly elevated calcium level in hypoxic compared to normoxic cells. Deeper understanding of mechanisms, through which hypoxia regulates intracellular calcium, could point towards the development of new therapeutic approaches to reduce or suppress the pathological effects of cellular hypoxia, such as those seen in stroke or ischemia. [ABSTRACT FROM AUTHOR]

Whole-cell and cell-attached patch clamp techniques were applied on isolated guinea pig ventricular myocytes to study the possible regulatory mechanisms of redox agent on persistent and transient sodium current related to hypoxia. The results showed that hypoxia for 15 min increased persistent sodium current ( I Na.P) and decreased transient sodium current ( I Na.T) at the same time, while 1 mmol/l of reduced glutathione (GSH) could reverse the increased I Na.P and the decreased I Na.T simultaneously. Both persistent and transient sodium channel activities could be reversed concurrently again by application of 1 mmol/l oxidized glutathione (GSSG). Hypoxia for 15 min decreased the action potential amplitude (APA) and shortened action potential duration at 90% repolarization (APD90) of ventricular papillary cells simultaneously, while 1 mmol/GSH could reverse the decreased APA and the shortened APD90 at the same time; 1 mmol/l GSSG strengthened the decrease of APA induced by hypoxia and attenuated the decurtation of APD90 induced by hypoxia compared with pure hypoxia. The correlation between I Na.P and I Na.T and the effects of GSH and GSSG on them suggested that during hypoxia, redox regulation played a tremendous part in sodium channel activity and that I Na.P and I Na.T might be charged by the same channel with different gating modes in guinea pig ventricular myocytes. Judging from their alterations during hypoxia and exposure to GSH and GSSG, we speculated that an interconversion might exist between I Na.P and I Na.T. That was when one of them was increased, the other was decreased, and vice versa. [ABSTRACT FROM AUTHOR]

Acute hypoxia increases ventilatory drive in conscious animals, resulting in tachycardia. Sustained hypoxia changes the initial chemoreflex ventilatory increase to secondary ventilatory depression, which then evokes a gradual secondary heart rate (HR) reduction. Prostacyclin (PGI2) release is known to potentiate α2-adrenoreceptor (α2-AR) mediated inhibition of sympathoactivation during ischaemia and hypoxia. We examined whether α2-AR mediated sympathoinhibition was responsible for limiting hypoxic heart rate increases during initial sympathoactivation, and subsequent secondary HR depression, and if PGI2 is required for sympathoinhibition of HR. The responses of unrestrained PGI2 synthase deficient (PGID) and wild type (WT) mice to acute hypoxia (10% O2 for 30 min) were investigated by simultaneous telemetry, whole body plethysmography and open-flow respirometry. PGID mice exhibited potentiated $${\mathop V\limits^ \cdot }_{E} $$ ( p < 0.007) after intraperitoneal vehicle injection ( n = 8), but not so HR responses compared to WT mice during sustained hypoxia. Idazoxan (α2-AR antagonist, i.p. bolus 3 mg/kg) pretreatment did not change hypoxic ventilatory response in either group, but significantly elevated hypoxic HR in WT mice only ( p < 0.013). Sodium meclofenamate (cyclooxygenase inhibition, i.p. bolus 25 mg/kg) pretreatment eliminated the potentiated $${\mathop V\limits^ \cdot }_{E} $$ of PGID and caused significant basal hypotension that led to a transient hypertensive response to hypoxia. From these results, we suggest that α2-AR activation is required for coupling HR to central inspiratory drive during acute hypoxia, and that PGI2 is required to enhance the inhibition of sympathoactivation. [ABSTRACT FROM AUTHOR]

5-Hydroxytryptamine (5-HT) is a potent pulmonary vasoconstrictor and mitogenic agent whose concentration increases in pulmonary hypertensive patients. Chronic hypoxia induces selective pulmonary arterial hypertension; therefore, we investigated chronic hypoxia effect on the calcium and contractile responses to 5-HT focusing on voltage-independent calcium influx in rat intrapulmonary arteries. Chronic hypoxia, induced by introducing rats in a hypobaric chamber for 3 weeks, potentiated the contraction to 5-HT and this effect was insensitive to nitrendipine. Calcium signal to 5-HT was characterized by a transient followed by a sustained phase in both normoxia and chronic hypoxia. The sustained phase was dependent on extracellular calcium and inhibited by lanthanum. RHC 80267, a specific inhibitor of diacylglycerol lipase, reduced the 5-HT-induced calcium influx in chronic hypoxia but not in normoxia. Furthermore, unlike gadolinium, RHC 80267 inhibited more the contraction to 5-HT in chronic hypoxia. Despite the apparent role of voltage-independent calcium channels in chronic hypoxia, Western blot and flow cytometry analyses demonstrated no variations in TRPC6 expression. This study shows for the first time that the 5-HT-induced calcium and contractile signals in chronic hypoxia are more dependent on a voltage-independent, RHC 80267-sensitive calcium influx and the hyperreactivity to 5-HT may thus be explained by this influx. [ABSTRACT FROM AUTHOR]

The adrenal medulla chromaffin cells (AMCs) secrete catecholamines in response to various types of stress. We examined the hypoxia-sensitivity of catecholamine secretion by rat foetal chromaffin cells in which the innervation by the splanchnic nerve is not established. The experiments were performed in primary cultured cells from two different ages of foetuses (F15 and F19). Membrane potential of AMCs was monitored with the patch clamp technique, and the catecholamine secretion was detected by amperometry. We found that: (1) AMCs from F19 foetuses showed hypoxia-induced catecholamine release. (2) This hypoxia-induced secretion is produced by membrane depolarization generated by an inhibition of Ca2+-activated K+ current [ I K(Ca)] current. (3) Chromaffin precursor cells from F15 foetuses secrete catecholamine. The quantal release is calcium-dependent, but the size of the quantum is reduced. (4) In the precursor cells, a hypoxia-induced membrane hyperpolarization is originated by an ATP-sensitive K+ current [ I K(ATP)] activation. (5) During the prenatal period, at F15, the percentage of the total outward current for I K(ATP) and I K(Ca) was 50 and 29.5%, respectively, whereas at F19, I K(ATP) is reduced to 14%, and I K(Ca) became 64% of the total current. We conclude that before birth, the age-dependent hypoxia response of chromaffin cells is modulated by the functional activity of KATP and KCa channels. [ABSTRACT FROM AUTHOR]

In healthy humans, changes in cardiac output are commonly accommodated with minimal change in pulmonary artery pressure. Conversely, exposure to hypoxia is associated with substantial increases in pulmonary artery pressure. In this study we used non-invasive measurement of an index of pulmonary artery pressure, the maximum systolic pressure difference across the tricuspid valve (Δ Pmax), to examine the pulmonary vascular response to changes in blood flow during both air breathing and hypoxia. We used Doppler echocardiography in 33 resting healthy humans breathing air over 6–24 h to measure spontaneous diurnal variations in Δ Pmax and cardiac output. Cardiac output varied by up to ~2.5 l/min; Δ Pmax varied little with cardiac output [0.61±0.74 (SD) mmHg min l−1]. Eight of the volunteers were also exposed to eucapnic hypoxia (end-tidal $$P_{{\rm O}_{2}} = 50\,{\text{mmHg}}$$) for 8 h. In this group Δ Pmax rose progressively from 21 mmHg to 37 mmHg over 8 h. By comparing diurnal variations in Δ Pmax during air breathing with changes in Δ Pmax during hypoxia in the same eight individuals, we concluded that only approximately 5% of the changes in Δ Pmax during hypoxia could be attributed to concurrent changes in cardiac output. The low sensitivity of Δ Pmax to changes in cardiac output makes it a useful index of hypoxic pulmonary vasoconstriction in healthy humans. [ABSTRACT FROM AUTHOR]

Even under anisotonic conditions, most cells can regulate their volume by mechanisms called regulatory volume decrease (RVD) and increase (RVI) after osmotic swelling or shrinkage, respectively. In contrast, the initial processes of necrosis and apoptosis are associated with persistent swelling and shrinkage. Necrotic volume increase (NVI) is initiated by uptake of osmolytes, such as Na+, Cl- and lactate, under conditions of injury, hypoxia, ischaemia, acidosis or lactacidosis. Persistence of NVI is caused by dysfunction of RVD due to impairment of volume-sensitive Cl- channels under conditions of ATP deficiency or lactacidosis. Both lactacidosis-induced RVD dysfunction and necrotic cell death are prevented by pretreatment of cells with the vacuolating cytotoxin-A (VacA) toxin protein purified from Helicobacter pylori, which forms a lactacidosis-resistant anion channel. Apoptotic volume decrease (AVD) is triggered by activation of K+ and Cl- conductances following stimulation with a mitochondrion-mediated or death receptor-mediated apoptosis inducer. Apoptotic cell death can be prevented by blocking the Cl- channels but not the K+-Cl- cotransporters. Thus, the volume regulatory anion channel plays, unless impaired, a cell-rescuing role in the necrotic process by ensuring RVD after swelling induced by necrotic insults, whereas normotonic activation of the anion channel plays a cell-killing role in the apoptotic process by triggering AVD following stimulation with apoptosis inducers. [ABSTRACT FROM AUTHOR]

The article presents abstracts from the papers presented at the 83rd annual meeting Deutsche Physiologische Gesellschaft scheduled from 14 to 17 March 2004, Leipzig, Germany. It informs that hypoxia inhibits alveolar Na-reabsorption. Scientists studied its significance on energy saving and whether hypoxia affected mitochondrial function. It further adds that to minimize oxygen consumption and metabolic energy expenditure, hypothermia is generally applied for organ preservation. Recent experiments provide evidence that oxidative stress during cold preservation and subsequent re-warming may limit reversibility of cellular function.

In cardiac myocytes of new-born rats, the degree of intercellular communication through gap junctional channels closely depends on the metabolic state of the cells. In contrast, in stably transfected HeLa cells expressing rat cardiac connexin43 (Cx43, the main channel-forming protein present in ventricular myocytes), a major part of junctional communication persisted in ATP-depleted conditions, in the presence of a metabolic inhibitor (KCN) or of a broad spectrum inhibitor of protein kinases (H7). However, another metabolic inhibitor, antimycin A, which like cyanide inhibits electron transfer in the respiratory chain, totally interrupted cell-to-cell communication between Cx43-HeLa cells, even in whole-cell conditions, when ATP (5 mM) was present. Antimycin A caused a modest increase in cytosolic calcium concentration; however, junctional uncoupling still occurred when this rise was prevented. Conditions of ischemic insult (e.g. ischemia or chemical hypoxia) frequently cause the activation of protein kinases, particularly of Src and MAP kinases, and such activations are known to markedly disrupt gap junctional communication. Antimycin-induced junctional uncoupling occurred even in the presence of inhibitors of these kinases. Antimycin A appears able to cause junctional uncoupling either through the ATP depletion it induces as a metabolic poison or via a direct action on gap junction constituents. [ABSTRACT FROM AUTHOR]

Membrane potential changes of atrial fibroblasts in response to mechanical stress have been considered to modulate the rhythmic electrical activity of healthy hearts. Our recent findings suggest that cardiac arrhythmia after infarction is related to enhanced susceptibility of the fibroblasts to physical stretch. In this study, we analysed the effect of hypoxia/reoxygenation, which are major components of tissue ischemia/reperfusion, on the membrane potential of atrial fibroblasts. Intracellular microelectrode recordings were performed together with isometric force measurements on isometrically contracting right atrial tissue preparations from adult rats. Lowering the oxygen tension in the perfusate from 80 kPa to 3.5 kPa reduced active force development and decreased the resting membrane potential of the cardiac fibroblasts from -23±5 mV to -5±2 mV (n=35). Application of gadolinium (40 μM) to inhibit non-selective cation channels prevented hypoxia-induced membrane depolarization of the fibroblasts. Reoxygenation of the myocardial tissue resulted in a transient increase of the resting membrane potential to maximally -60±8 mV. These findings indicate that transmembrane currents in atrial fibroblasts are sensitive to changes in tissue oxygenation. In conclusion, altered electro-mechanical function of the ischemic heart may possibly involve changes of the membrane potential of the cardiac fibroblasts. [ABSTRACT FROM AUTHOR]

We have previously shown that subjects exposed to acute hypobaric hypoxia display an erythrocyte membrane protein band 3 with an increased susceptibility to proteolytic degradation. We suggested it was due to an oxidative damage of band 3. We now report that exposure to hypobaric hypoxia followed by reoxygenation affects protein band 3 functions such as anion transport and binding of glyceraldehyde-3P-dehydrogenase. Transport capacity was assessed with the fluorescent probe 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino] ethanesulfonate (NBD-taurine). Binding capacity was evaluated from the activity of the membrane-associated enzyme. Healthy young men were exposed for 20 min to hypobaric hypoxia, simulating an altitude of 4,500 m above sea level and after recompression band 3 function was assessed. An inhibition of band 3 anion transport function and a decrease in the binding of glyceraldehyde-3P-dehydrogenase to band 3 were observed. Evidence is given supporting the hypothesis that functional alteration of band 3 is due to its oxidative modification originated as a consequence of the exposure to hypobaric hypoxia and further reoxygenation. [ABSTRACT FROM AUTHOR]

At 0.1–1 µM, U50488H, a κ-opioid receptor agonist, inhibited the stimulatory effects of 1 µM isoprenaline, a β-adrenoceptor agonist, on the electrically induced intracellular Ca2+ ([Ca2+]i) transient and cAMP accumulation ("cross talk" between κ-opioid receptors and β-adrenoceptors) in the presence of 1 µM ICI118,551, a β2-adrenoceptor antagonist in ventricular myocytes from both normoxic and chronically hypoxic rats. Pretreatment with 20 µg/ml cholera toxin increased the ADP-ribosylation of Gsα subunits and the electrically induced [Ca2+]i transient in both normoxic and chronically hypoxic rats. The effects of cholera toxin were inhibited by 1 µM U50488H and the inhibitory effect of U50488H was attenuated in chronically hypoxic rats. Similarly, 1 µM forskolin also increased the electrically induced [Ca2+]i transient and cAMP accumulation, which were both inhibited by U50488H, in both normoxic and chronically hypoxic rats. The inhibitory effects of 1 µM U50488H were significantly attenuated in chronically hypoxic rats. The results are novel findings, in that the "cross talk" between κ-opioid receptors and β-adrenoceptors is attenuated following chronic hypoxia. The attenuation may be due to decreased responses of Gs-protein and adenylyl cyclase to κ-opioid receptor activation in addition to desensitization of the receptor itself. [ABSTRACT FROM AUTHOR]

Endothelin-1 (ET-1) excites carotid body (CB) chemoreceptors and induces mitosis of the chemoreceptors in chronic hypoxia. The aim of the present study was to examine the hypothesis that up-regulation of both ETA receptor and endogenous ET-1 expression in CB chemoreceptors enhances the response of intracellular Ca2+ to ET-1 following adaptation to chronic hypoxia (10% inspired O2 for 3–4 weeks). Cytosolic free [Ca2+] ([Ca2+]i) in type-I (glomus) cells freshly dissociated from rat CBs was measured by spectrofluorometry. Application of exogenous ET-1 (1–100 nM) concentration-dependently elevated [Ca2+]i in the glomus cells. This response to ET-1 (100 nM) was 49% greater in the chronically hypoxic (CH) group. The ET-1 response was abolished completely by the ETA receptor antagonist BQ610 (1 µM), but not by the ETB antagonist BQ788 (1 µM). The transient [Ca2+]i elevation induced by caffeine (30 mM) in the normoxic group was similar to that in the CH group, suggesting no differences in the intracellular Ca2+ stores. In situ hybridization with a digoxigenin-labelled antisense ETA receptor mRNA oligonucleotide probe revealed very intense and ubiquitous specific expression of ETA receptors in the lobules of glomus cells in the CH group, whereas staining in normoxic controls was light. Immunohistochemical studies revealed intense cytoplasmic staining for ET-1-immunoreactivity in most of the cell clusters in glomera in the CBs of CH rats but was faint in normoxic CBs. These findings indicate increased expression of both the ETA receptor and ET-1 in CB chemoreceptors during chronic hypoxia. Taken together, our results suggest that the [Ca2+]i response to ET-1 in rat CB chemoreceptors is augmented by up-regulation of ETA receptors and ET-1 expression. The enhancement of the paracrine/autocrine effect of ET-1 on the chemoreceptors is consistent with an excitatory and mitogenic role of the ET-1 and ETA receptor in the CB during chronic hypoxia. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factors (HIFs) locate to HIF-binding sites (HBSs) within the hypoxia-response elements (HREs) of oxygen-regulated genes. Whereas HIF-1α is expressed ubiquitously, HIF-2α is found primarily in the endothelium, similar to endothelin-1 (ET-1) and fms-like tyrosine kinase 1 (Flt-1), the expression of which is controlled by HREs. We identified an unique sequence alteration in both ET-1 and Flt-1 HBSs not found in other HIF-1 target genes, implying that these HBSs might cause binding of HIF-2 rather than HIF-1. However, electrophoretic mobility shift assays showed HIF-1 and HIF-2 DNA complex formation with the unique ET-1 HBS to be about equal. Both DNA-binding and hypoxic activation of reporter genes using the ET-1 HBS was decreased compared with transferrin and erythropoietin HBSs. The Flt-1 HBS was non-functional when assayed in isolation, suggesting that additional factors are required for hypoxic up-regulation via the reported Flt-1 HRE. Interestingly, HIF-1 activity could be restored fully by point-mutating the ET-1 (but not the Flt-1) HBS, suggesting that the wild-type ET-1 HBS attenuated the full hypoxic response known from other oxygen-regulated genes. Such a mechanism might serve to limit the expression of this potent vasoconstrictor in hypoxia. [ABSTRACT FROM AUTHOR]

Male Wistar rats aged 4 weeks, were subjected to hypobaric hypoxia (barometric pressure 505 hPa, PI,O2 106 hPa) or to diet restriction (reproducing the effect of hypoxia-induced anorexia) for 4 weeks. Each group (control, hypoxic, pair-fed, n=16), was divided into two sub-groups housed individually in either normal cages or cages with running wheels allowing evaluation of voluntary activity (n=8 each). The skinned-fibre technique was used to evaluate the functional properties of myofibrillar mitochondria from right and left ventricles in situ. The oxidative fibres from the soleus and diaphragm muscles were also investigated for comparison. Analysis of variance did not detect any significant effect of voluntary running activity. With calorie restriction, the maximal respiratory rate (Vmax) in the presence of 1 mM adenosine 5′-diphosphate (ADP) in myocardial fibres fell significantly (by about 25%) but was unchanged in skeletal myocytes. Following hypoxia, Vmax in myocardial fibres increased by 25% compared with the calorie restricted group and in soleus and diaphragm muscle fibres by about 30% compared with control. In myocardial fibres of control rats, creatine (20 mM) increased the sub-maximal respiratory rate by 80% in the presence of 0.1 mM ADP. Under calorie restriction or hypoxia the stimulatory effect was significantly reduced to 34–56%. This alteration was due to a decrease in the apparent Michaelis-Menten constant (Km) of mitochondrial respiration for ADP evaluated in the absence of creatine, while the Km in presence of creatine 20 mM was unchanged. In conclusion, reduced food intake decreased the oxidative capacity (Vmax) and the apparent Km for ADP of mitochondria in both left and right ventricles. Chronic hypoxia per se was responsible for an increase in the oxidative capacity of all oxidative muscles but did not exert significant effects on the control of respiration by ADP and creatine in myocardium. [ABSTRACT FROM AUTHOR]

Ventilatory acclimatization to altitude is associated with a progressive increase in ventilation, a progressive decrease in end-tidal PCO2 and a progressive increase in the acute ventilatory sensitivity to hypoxia. Ventilatory acclimatization has been observed with mild exposure to hypoxia when the duration of exposure has been of some length (e.g. days), and with shorter duration exposures (e.g. 8 h) when the degree of hypoxia has been more severe. The purpose of this study was to determine whether short-duration exposures to very mild hypoxia, such as are commonly associated with the reduction in cabin pressure during commercial airline flight, can also induce some degree of ventilatory acclimatization. Twelve subjects were exposed in a chamber to both 8 h mild hypoxia (inspired PO2 127 mmHg) and 8 h air-breathing as a control. Exposures were on different days in random order. Following the hypoxic exposure, there was a significant reduction in end-tidal PCO2 during air breathing (from 39.2±1.8 to 38.1±1.5 mmHg, mean±SD, P<0.05), and a significant increase in ventilatory sensitivity to hypoxia (from 0.84±0.54 l/min/% to 1.13±0.66 l/min/%, P<0.05). We conclude that short-term exposures to very mild hypoxia do induce significant acclimatization within the respiratory control system. [ABSTRACT FROM AUTHOR]

T-type Ca2+ channels are expressed in a wide variety of central and peripheral neurons and play an important role in neuronal firing and rhythmicity. Here we examined the effects of hypoxia on the recently cloned T-type Ca2+ channel α1G, α1H and α1I subunits, stably expressed in HEK 293 cells. In cells expressing the human α1H or the rat α1I subunit, Ca2+ channel currents were inhibited reversibly by hypoxia (PO2<110 mmHg). The degree of inhibition was more marked in cells expressing the α1H subunit. This hypoxic inhibition was not voltage dependent. In cells expressing the rat α1G subunit, hypoxia caused no detectable reduction in Ca2+ channel activity. Regardless of the channel type examined, hypoxia was without effect on the kinetic properties of the Ca2+ current (activation, inactivation and deactivation) or on steady-state inactivation. Ca2+ current through the α1H subunit was enhanced by the reducing agent reduced glutathione (GSH; 2 mM) and inhibited by oxidised glutathione (GSSG; 2 mM). In contrast, Ca2+ current through the α1G subunit was unaffected by GSH. In α1H cells, neither GSH nor GSSG had any effect on the ability of hypoxia to reduce Ca2+ current amplitudes. Thus, different members of the T-type Ca2+ channel family are differently regulated by hypoxia and redox agents. Hypoxic regulation of the α1H subunit appears to be independent of changes in levels of the intracellular redox couple GSSG:GSH. [ABSTRACT FROM AUTHOR]

Fatigue studies of isolated, intact muscles typically utilize solutions saturated with O2. However, under in vivo fatiguing conditions, less oxygen is delivered to the muscles and they actually experience hypoxia. No studies to date have correlated the effects of acute hypoxia on the isometric contractile properties of intact muscles, skinned fibers isolated from the same muscles, and the cellular content of specific muscle proteins. Therefore, we have studied the effects of in vitro acute hypoxia on the fatigability of intact diaphragm muscle strips and on the isometric contractile properties of single Triton-skinned fibers isolated from control and hypoxic diaphragm muscles. We found that hypoxia and fatiguing stimulation per se affect the tetanic force of intact muscle strips without exhibiting any significant deleterious effects on the calcium-activated force of skinned muscle fibers dissected from the intact muscles. In contrast, fatiguing stimulation under hypoxic conditions decreased both the tetanic force of muscle strips and the calcium-activated force of skinned muscle fibers. Gel electrophoresis of muscles subjected to hypoxia and hypoxic-fatigue revealed that there is a significant reduction in three protein bands when compared to control muscles. Protein modification may be the underlying mechanism of muscle fatigue under physiologic conditions. [ABSTRACT FROM AUTHOR]

An abstract of the article "Time dependences of hypoxia-induced rat carotid chemosensor activity in vitro" is presented. The study aims to characterize these adaptation-like time dependences at different hypoxic levels in consideration of fatigue of the sensoric tissue. Unlike in situ, the isolated superfused carotid chemosensor responds to acute and constant hypoxia with transient increase and subsequent decrease of carotid sinus nerve (CSN) activity.

An abstract of the research "Hypoxia activates the adrenomedullin system in vivo," by P. Sandner and A. Kurtz is presented. The study aimed to investigate the influence of tissue hypoxygenation the adrenomedullin system in vivo. It explains that messenger RNA levels for ADM and its receptor were assessed in diverse organs by ribonuclease protection assay.

An abstract of the article "Hypoxia stimulates von Willebrand factor exocytosis at unaltered intracellular pH" is presented. It focuses on the causes of ischemia on human umbilical venous endothelial cells. The causes of ischemia has been examined in two strategies including extracellular acidosis on intracellular pH and hypoxia on the release of von Willebrand factor laid in Weibel-Palade bodies.

The article presents an abstract of the study "Effects of hypoxia on membrane conductance, Cai and Cli of alveolar epithelial cells." It discusses how hypoxia inhibits the cation transport of alveolar epithelial cells as a mechanism contributing to hypoxic pulmonary edema formation. The result of the study suggests responses to hypoxia might be activated by membrane depolarization.