Cytoplasmic pH in pulmonary macrophages: recovery from acid load is Na+ independent and NEM sensitive

Intestinal Amino Acid Transport and Metabolic Health

Amino acids derived from protein digestion are important nutrients for the growth and maintenance of organisms. Approximately half of the 20 proteinogenic amino acids can be synthesized by mammalian organisms, while the other half are essential and must be acquired from the nutrition. Absorption of amino acids is mediated by a set of amino acid transporters together with transport of di- and tripeptides. They provide amino acids for systemic needs and for enterocyte metabolism. Absorption is largely complete at the end of the small intestine. The large intestine mediates the uptake of amino acids derived from bacterial metabolism and endogenous sources. Lack of amino acid transporters and peptide transporter delays the absorption of amino acids and changes sensing and usage of amino acids by the intestine. This can affect metabolic health through amino acid restriction, sensing of amino acids, and production of antimicrobial peptides.

Simulated biological fluids - a systematic review of their biological relevance and use in relation to inhalation toxicology of particles and fibres

The use of simulated biological fluids (SBFs) is a promising in vitro technique to better understand the release mechanisms and possible in vivo behaviour of materials, including fibres, metal-containing particles and nanomaterials. Applications of SBFs in dissolution tests allow a measure of material biopersistence or, conversely, bioaccessibility that in turn can provide a useful inference of a materials biodistribution, its acute and long-term toxicity, as well as its pathogenicity. Given the wide range of SBFs reported in the literature, a review was conducted, with a focus on fluids used to replicate environments that may be encountered upon material inhalation, including extracellular and intracellular compartments. The review aims to identify when a fluid design can replicate realistic biological conditions, demonstrate operation validation, and/or provide robustness and reproducibility. The studies examined highlight simulated lung fluids (SLFs) that have been shown to suitably replicate physiological conditions, and identify specific components that play a pivotal role in dissolution mechanisms and biological activity; including organic molecules, redox-active species and chelating agents. Material dissolution was not always driven by pH, and likewise not only driven by SLF composition; specific materials and formulations correspond to specific dissolution mechanisms. It is recommended that SLF developments focus on biological predictivity and if not practical, on better biological mimicry, as such an approach ensures results are more likely to reflect in vivo behaviour regardless of the material under investigation.

Pulmonary myeloid cell uptake of biodegradable nanoparticles conjugated with an anti-fibrotic agent provides a novel strategy for treating chronic allergic airways disease

Asthma (chronic allergic airways disease, AAD) is characterized by airway inflammation (AI), airway remodeling (AWR) and airway hyperresponsiveness (AHR). Current treatments for AAD mainly focus on targeting AI and its contribution AHR, with the use of corticosteroids. However, there are no therapies for the direct treatment of AWR, which can contribute to airway obstruction, AHR and corticosteroid resistance independently of AI. The acute heart failure drug, serelaxin (recombinant human gene-2 relaxin, RLX), has potential anti-remodeling and anti-fibrotic effects but only when continuously infused or injected to overcome its short half-life. To alleviate this limitation, we conjugated serelaxin to biodegradable and noninflammatory nanoparticles (NP-RLX) and evaluated their therapeutic potential on measures of AI, AWR and AHR, when intranasally delivered to a preclinical rodent model of chronic AAD and TGF-β1-stimulated collagen gel contraction from asthma patient-derived myofibroblasts. NP-RLX was preferentially taken-up by CD206⁺-infiltrating and CD68⁺-tissue resident alveolar macrophages. Furthermore, NP-RLX ameliorated the chronic AAD-induced AI, pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), chemokines (CCL2, CCL11) and the pro-fibrotic TGF-β1/IL-1β axis on AWR and resulting AHR, as well as human myofibroblast-induced collagen gel contraction, to a similar extent as unconjugated RLX. Hence, NP-RLX represents a novel strategy for treating the central features of asthma.

The acute effects of thermogenic fitness drink formulas containing 140 mg and 100 mg of caffeine on energy expenditure and fat metabolism at rest and during exercise

BACKGROUND

Thermogenic fitness drink formulas (TFD) have been shown to increase energy expenditure and markers of lipid metabolism. The purpose of the current study was to compare TFD formulas containing different caffeine concentrations versus a placebo drink on energy expenditure and lipid metabolism at rest and during exercise.

METHODS

Thirty-two recreationally active participants (22.9 ± 0.7 y, 167.1 ± 1.4 cm, 68.8 ± 2.0 kg, 24.0 ± 1.2% fat) who were regular caffeine consumers, participated in this randomized, double-blind, crossover design study. Participants reported to the laboratory on three occasions, each of which required consumption of either a TFD containing 140 mg or 100 mg of caffeine or a placebo. Baseline measurements of resting energy expenditure (REE) and resting fat oxidation (RFO) were assessed using indirect calorimetry as well as measurements of serum glycerol concentration. Measurements were repeated at 30, 60, 90 min post-ingestion. Following resting measures, participants completed a graded exercise test to determine maximal oxygen uptake (V̇O2max), maximal fat oxidation (MFO) and the exercise intensity that elicits MFO (Fatmax), and total energy expenditure (EE).

RESULTS

A significant interaction was shown for REE (p < 0.01) and RFO (p < 0.01). Area under the curve analysis showed an increased REE for the 140 mg compared to the 100 mg formula (p = 0.02) and placebo (p < 0.01) and an increased REE for the 100 mg formula compared to placebo (p = 0.02). RFO significantly decreased for caffeinated formulas at 30 min post ingestion compared to placebo and baseline (p < 0.01) and significantly increased for the 140 mg formula at 60 min post-ingestion (p = 0.03). A main effect was shown for serum glycerol concentrations over time (p < 0.01). No significant differences were shown for V̇O2max (p = 0.12), Fatmax (p = 0.22), and MFO (p = 0.05), and EE (p = 0.08) across drinks.

CONCLUSIONS

Our results suggest that TFD formulas containing 100 and 140 mg of caffeine are effective in increasing REE and that a 40 mg of caffeine difference between the tested formulas may impact REE and RFO in healthy individuals within 60 min of ingestion.

The volume-regulated anion channel (LRRC8) in nodose neurons is sensitive to acidic pH

The leucine rich repeat containing protein 8A (LRRC8A), or SWELL1, is an essential component of the volume-regulated anion channel (VRAC) that is activated by cell swelling and ionic strength. We report here for the first time to our knowledge its expression in a primary cell culture of nodose ganglia neurons and its localization in the soma, neurites, and neuronal membrane. We show that this neuronal VRAC/SWELL1 senses low external pH (pH_o) in addition to hypoosmolarity. A robust sustained chloride current is seen in 77% of isolated nodose neurons following brief exposures to extracellular acid pH. Its activation involves proton efflux, intracellular alkalinity, and an increase in NOX-derived H₂O_2. The molecular identity of both the hypoosmolarity-induced and acid pH_o-conditioned VRAC as LRRC8A (SWELL1) was confirmed by Cre-flox-mediated KO, shRNA-mediated knockdown, and CRISPR/Cas9-mediated LRRC8A deletion in HEK cells and in primary nodose neuronal cultures. Activation of VRAC by low pH_o reduces neuronal injury during simulated ischemia and N-methyl-D-aspartate-induced (NMDA-induced) apoptosis. These results identify the VRAC (LRRC8A) as a dual sensor of hypoosmolarity and low pH_o in vagal afferent neurons and define the mechanisms of its activation and its neuroprotective potential.

Absence of Expression of c-sis and Transforming Growth Factor-β mRNA in Malignant Fibrous Histiocytoma

Total RNA was extracted from five malignant fibrous histiocytomas and two benign fibrohistiocytic lesions and assayed for mRNA expressions for transforming growth factor beta (TGF-β) and c-sis by Northern blot analysis. Production of both of these has been associated with cells of monocyte-macrophage lineage, and these factors have been shown to be important in physiologic mesenchymal cell proliferation. No mRNA expression of either TGF-β or c-sis was identified in any of the fibrohistiocytic tumor samples. The lack of expression of TGF-β and c-sis may be consistent with a nonhistiocytic origin of malignant fibrous histiocytoma, or may reflect transformation- associated loss of the normal molecular mechanisms of mesenchymal proliferation. The absence of c-sis mRNA expression can be reconciled with the prior immunohisto chemical demonstration of platelet-derived growth factor in tumor cells of malignant fibrous histiocytoma. Int J Surg Pathol(2):117-122, 1993

Targeting V-ATPase in primary human monocytes by archazolid potently represses the classical secretion of cytokines due to accumulation at the endoplasmic reticulum

The macrolide archazolid inhibits vacuolar-type H(+)-ATPase (V-ATPase), a proton-translocating enzyme involved in protein transport and pH regulation of cell organelles, and potently suppresses cancer cell growth at low nanomolar concentrations. In view of the growing link between inflammation and cancer, we investigated whether inhibition of V-ATPase by archazolid may affect primary human monocytes that can promote cancer by sustaining inflammation through the release of tumor-promoting cytokines. Human primary monocytes express V-ATPase, and archazolid (10-100nM) increases the vesicular pH in these cells. Archazolid (10nM) markedly reduced the release of pro-inflammatory (TNF-α, interleukin-6 and -8) but also of anti-inflammatory (interleukin-10) cytokines in monocytes stimulated with LPS, without affecting cell viability up to 1000nM. Of interest, secretion of interleukin-1β was increased by archazolid. Comparable effects were obtained by the V-ATPase inhibitors bafilomycin and apicularen. The phosphorylation of p38 MAPK and ERK-1/2, Akt, SAPK/JNK or of the inhibitor of NFκB (IκBα) as well as mRNA expression of IL-8 were not altered by archazolid in LPS-stimulated monocytes. Instead, archazolid caused endoplasmic reticulum (ER) stress response visualized by increased BiP expression and accumulation of IL-8 (and TNF-α) at the ER, indicating a perturbation of protein secretion. In conclusion, by interference with V-ATPase, archazolid significantly affects the secretion of cytokines due to accumulation at the ER which might be of relevance when using these agents for cancer therapy.

A type VI secretion system regulated by OmpR in Yersinia pseudotuberculosis functions to maintain intracellular pH homeostasis

Type VI secretion systems (T6SSs) which widely distributed in Gram-negative bacteria have been primarily studied in the context of cell interactions with eukaryotic hosts or other bacteria. We have recently identified a thermoregulated T6SS4 in the enteric pathogen Yersinia pseudotuberculosis. Here we report that OmpR directly binds to the promoter of T6SS4 operon and regulates its expression. Further, we observed that the OmpR-regulated T6SS4 is essential for bacterial survival under acidic conditions and that its expression is induced by low pH. Moreover, we showed that T6SS4 plays a role in pumping H(+) out of the cell to maintain intracellular pH homeostasis. The acid tolerance phenotype of T6SS4 is dependent on the ATPase activity of ClpV4, one of the components of T6SS4. These results not only uncover a novel strategy utilized by Y. pseudotuberculosis for acid resistance, but also reveal that T6SS, a bacteria secretion system known to be functional in protein transportation has an unexpected function in H(+) extrusion under acid conditions.

DNA hypermethylation and 1p Loss silence NHE-1 in oligodendroglioma

Oligodendroglioma is characterized by mutations of IDH and CIC, 1p/19q loss, and slow growth. We found that NHE-1 on 1p is silenced in oligodendrogliomas secondary to IDH-associated hypermethylation and 1p allelic loss. Silencing lowers intracellular pH and attenuates acid load recovery in oligodendroglioma cells. Others have shown that rapid tumor growth cannot occur without NHE-1-mediated neutralization of the acidosis generated by the Warburg glycolytic shift. Our findings show for the first time that the pH regulator NHE-1 can be silenced in a human cancer and also suggest that pH deregulation may contribute to the distinctive biology of human oligodendroglioma.

Phosphoinositide 3-kinase-dependent regulation of Na+/H+ exchanger in dendritic cells

Dendritic cells (DCs), antigen-presenting cells that are able to initiate primary immune responses and to establish immunological memory, are activated by exposure to bacterial lipopolysaccharides (LPS), which leads to cell swelling, triggering ROS formation and stimulating migration. The function of DCs is regulated by the phosphoinositide 3 (PI3) kinase pathway. On the other hand, PI3 kinase is an important regulator of diverse transporters including the Na(+)/H(+) exchanger (NHE). The present study was performed to elucidate the role of PI3 kinase in NHE activity, cell volume, ROS formation, and migration. To this end, DCs were isolated from murine bone marrow, cytosolic pH (pH(i)) determined utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein fluorescence, Na(+)/H(+) exchanger activity from the Na(+)-dependent realkalinization after an ammonium pulse, cell volume from forward scatter in fluorescence-activated cell sorter analysis, ROS production from 2',7'-dichlorodihydrofluorescein diacetate fluorescence, and migration utilizing transwell migration assays. Exposure of DCs to LPS led within 4 h to a gradual cytosolic acidification paralleled by a transient time- and dose-dependent increase of Na(+)/H(+) exchanger activity, cell swelling, enhanced ROS production, and stimulation of migration. The PI3K inhibitors Wortmannin (1 μM) or LY294002 (10 μM) significantly blunted the effects of LPS on NHE activity, cell volume, ROS production, and migration. The present observations disclose a critical role of PI3K signaling in the regulation of DC function following exposure to LPS.

Insulin sensitivity is related to fat oxidation and protein kinase C activity in children with acute burn injury

Impaired fatty acid oxidation occurs with type 2 diabetes and is associated with accumulations of intracellular lipids, which may increase diacylglycerol (DAG), stimulate protein kinase C activity, and inactivate insulin signaling. Glucose and fat metabolism are altered in burn patients, but have never been related to intracellular lipids or insulin signaling. Thirty children sustaining >40% total body surface area burns were studied acutely with glucose and palmitate tracer infusions and a hyper-insulinemic euglycemic clamp. Muscle triglyceride, DAG, fatty acyl CoA, and insulin signaling were measured. Liver and muscle triglyceride levels were measured with magnetic resonance spectroscopy. Muscle samples from healthy children were controls for DAG concentrations. Insulin sensitivity was reduced and correlated with whole body palmitate beta-oxidation (P = .004). Muscle insulin signaling was not stimulated by hyper-insulinemia. Tissue triglyceride concentrations and activated protein kinase C-beta were elevated, whereas the concentration of DAG was similar to the controls. Free fatty acid profiles of muscle triglyceride did not match DAG. Insulin resistance following burn injury is accompanied by decreased insulin signaling and increased protein kinase C-beta activation. The best metabolic predictor of insulin resistance in burned patients was palmitate oxidation.

Changes of characteristics of preoptic neurons and NA metabolism in hypothalamus of ground squirrel (Citelleus Dautieus) in different seasons and hibernating phases

The unit firing activities of neurons in the preoptic area (POA) of ground squirrel hypothalamic tissue slices were recorded and the metabolism of NA in hypothalamus was measured with high performance liquid chromatography (HPLC). Thermosensitivity, proportions, the critical temperature (Tc) and the lowest temperature (TL) of firing activity of the above-mentioned neurons, and NA metabolism in hypothalamus were compared in different seasons and hibernating phases. In comparison with that in summer euthermar, it was shown that (i) the percentage and thermosensitivity of the POA neurons varied respectively in the hibernating phases; (ii) TL and Tc of the POA neurons in winter, both euthermar and hibernation, were markedly decreased; (iii) the POA neurons in hibernation became much more sensitive to NA, and the response of cold-sensitive neurons to NA changed from inhibiting pattern in summer to exciting one in hibernation; (iv) the contents and metabolism of NA in hypothalamus decreased significantly in the entering phase and deep hibernation phase, while the metabolism of NA increased remarkably in the arousal phase. These changes might explain the regulatory mechanism how ground squirrel actively decreases body temperature (Tb) in entering into hibernation and quickly recovers body temperature in arousal phase.

Ventilatory response to hypoxia during endotoxemia in young rats: role of nitric oxide

Administration of Escherichia coli endotoxin attenuates the ventilatory response to hypoxia (VRH) in newborn piglets, but the mechanisms responsible for this depression are not clearly understood. Nitric oxide (NO) production increases during sepsis and elevated NO levels can inhibit carotid body function. The role of endothelial NO on the VRH during endotoxemia was evaluated in 26 young rats. Minute ventilation (VE) and oxygen consumption (VO2) were measured in room air (RA) and during 30 min of hypoxia (10% O2) before and after E. coli endotoxin administration. During endotoxemia, animals received placebo (PL, n = 8); a nonselective nitric oxide synthase (NOS) inhibitor (NG-nitro-L-arginine methyl ester, L-NAME, n = 9), or a neuronal NOS (nNOS) inhibitor (7-nitroindazole, 7-NI, n = 9). During endotoxemia, a larger increase in VE was observed only during the first min of hypoxia in the L-NAME group when compared with PL or 7-NI (p < 0.001). VRH was similar in the PL and 7-NI groups. A larger decrease in VO2 at 30 min of hypoxia was observed in L-NAME and 7-NI groups when compared with PL (p < 0.03). These data demonstrate that the attenuation of the early VRH during endotoxemia is in part mediated by an inhibitory effect of endothelial NO on the respiratory control mechanisms.

Prognostic value of platelet-derived growth factor in patients with severe sepsis

PRIMARY OBJECTIVE

Platelet-derived growth factor-BB (PDGF-BB) has been shown to promote the structural integrity of the vessel wall and to increase wound healing capacity. Aim of the present study was to determine the role of PDGF-BB in the context of outcome of septic patients. Furthermore, the effect of treatment with recombinant human activated protein C (rhAPC) on plasma levels of PDGF-BB in severe sepsis was evaluated as well as the in vitro effect of rhAPC on PDGF-BB-release from human endothelial cells (HUVEC). RESEARCH DESIGN, METHODS AND PROCEDURES: PDGF-BB levels were measured in 46 patients on day 3 of severe sepsis. Twenty-one of these patients received treatment with rhAPC. The in vitro effect of rhAPC on PDGF-BB-messenger RNA synthesis and release of PDGF-BB into supernatants was measured by reverse transcriptase-polymerase chain reaction and ELISA-methods.

MAIN OUTCOMES AND RESULTS

Survivors of severe sepsis presented with higher PDGF-BB levels than non-survivors (p < 0.05). Septic patients with PDGF-BB levels below 200 pg/ml were 7.3 times more likely (RR = 7.3, 95% CI: 1.4-44.5; p < 0.05) to die from sepsis than patients with higher PDGF-BB values. RhAPC (1-10 microg/ml) stimulated endothelial PDGF-BB-messenger RNA transcription and PDGF-BB-release in vitro. Plasma levels of PDGF-BB in patients receiving rhAPC were significantly (p < 0.01) higher (median 277.7; 25-75th percentiles: 150.5-414.4 pg/ml) than in patients not treated with rhAPC (median: 125.6; 25-75th percentiles: 55.3-344.7 pg/ml).

CONCLUSIONS

The ability of rhAPC to upregulate endothelial PDGF-BB production may represent a new molecular mechanism by which rhAPC controls vessel wall homeostasis and increases tissue healing capacity in severe sepsis. PDGF-BB may serve as useful laboratory marker to predict survival in patients presenting with severe sepsis.

Dynamics of starvation in humans

A differential equation model describing the dynamics of stored energy in the form of fat mass, lean body mass and ketone body mass during prolonged starvation is developed. The parameters of the model are estimated using available data for 7 days into starvation. A simulation of energy stores for a normal individual with body mass index between 19 and 24 and an obese individual with body mass index over 30 are calculated. The length of time the obese subject can survive during prolonged starvation is estimated using the model.

The sodium/hydrogen exchanger: a possible mediator of immunity

Immune cells such as macrophages and neutrophils provide the first line of defence of the immune system using phagocytosis, cytokine and chemokine synthesis and release, as well as Reactive Oxygen Species (ROS) generation. Many of these functions are positively coupled with cytoplasmic pH (pHi) and/or phagosomal pH (pHp) modification; an increase in pHi represents an important signal for cytokine and chemokine release, whereas a decrease in pHp can induce an efficient antigen presentation. However, the relationship between pHi and ROS generation is not well understood. In immune cells two main transport systems have been shown to regulate pHi: the Na+/H+ Exchanger (NHE) and the plasmalemmal V-type H+ ATPase. NHE is a family of proteins which exchange Na+ for H+ according to their concentration gradients in an electroneutral manner. The exchanger also plays a key role in several other cellular functions including proliferation, differentiation, apoptosis, migration, and cytoskeletal organization. Since not much is known on the relationship between NHE and immunity, this review outlines the contribution of NHE to different aspects of innate and adaptive immune responses such as phagosomal acidification, NADPH oxidase activation and ROS generation, cytokine and chemokine release as well as T cell apoptosis. The possibility that several pro-inflammatory diseases may be modulated by NHE activity is evaluated.

A macrophage cell model for pH and volume regulation

A whole-cell model of a macrophage (mphi) is developed to simulate pH and volume regulation during a NH4Cl prepulse challenge. The cell is assumed spherical, with a plasma membrane that separates the cytosolic and extracellular bathing media. The membrane contains background currents for Na+, K+ and Cl-, a Na(+)-K+ pump, a V-type H(+)-extruder (V-ATPase), and a leak pathway for NH4+. Cell volume is controlled by instantaneous osmotic balance between cytosolic and extracellular osmolytes. Simulations reveal that the mphi model can mimic alterations in measured pH(i) and cell volume (Vol(i)) data during and after delivery of an ammonia prepulse, which induces an acid load within the cell. Our analysis indicates that there are substantial problems in quantifying transporter-mediated H+ efflux solely from experimental observations of pH(i) recovery, as is commonly done in practice. Problems stemming from the separation of effects arise, since there is residual NH4+ dissociation to H+ inside the mphi during pH(i) recovery, as well as, proton extrusion via the V-ATPase. The core assumption of conventional measurement techniques used to estimate the H+ extrusion current (I(H)) is that the recovery phase is solely dependent on transporter-mediated H+ extrusion. However, our model predictions suggest that there are major problems in using this approach, due to the complex interactions between I(H), NH3/NH4+ buffering and NH3/NH4+ efflux during the active acid extrusion phase. That is, the conventional buffer capacity-based I(H) estimation must also take into account the perturbation that a prepulse challenge brings to the cytoplasmic acid buffer itself. The importance of this whole-cell model of mphipH(i) and volume regulation lies in its potential for extension to the characterization of several other types of non-excitable cells, such as the microglia (brain macrophage) and the T-lymphocyte.

Maximizing acute fat utilization: effects of exercise, food, and individual characteristics

In discussion of the physiological mechanisms that regulate fat metabolism, and with consideration of the metabolic stimuli that modulate substrate metabolism, the issue of how an acute state of negative lipid balance can be maximized is addressed. The regulation of lipolysis by catecholamines and insulin is reviewed, and the mechanisms of fatty acid mobilization and uptake by muscle are also briefly discussed. The implications of substrate availability and the hormonal response during physiological states such as fasting, exercise, and after food intake are also addressed, with particular regard to the influences on fatty acid mobilization and/or oxidation from eliciting these stimuli conjointly. Finally, a brief discussion is given of both the nature of exercise and the exercising individual, and how these factors influence fat metabolism during exercise. It is also a primary thrust of this paper to underline gaps in the existing literature with regard to exercise timing concerning food ingestion for maximizing acute lipid utilization.

Innate host defense of the lung: effects of lung-lining fluid pH

Lung-lining fluid (LLF) is a primary constituent of the pulmonary host defense system. It is distributed continuously throughout the respiratory tract but is heterogeneous regarding its chemistry and physiology between the conducting airways and alveoli. The conducting airways are lined with airway surface liquid (ASL), a mucus gel-aqueous sol complex that interacts functionally with epithelial cilia as the mucociliary escalator. The alveoli are lined with alveolar subphase fluid (AVSF) and pulmonary surfactant. AVSF sterility is maintained in part by the phagocytic activity of resident alveolar macrophages. Normal ASL and AVSF are both more acidic than blood plasma. However, the details of acid-base regulation differ between the two media. Appreciable transepithelial acid-base flux is possible across the airway epithelium, whereas the alveolar epithelium is relatively impermeable to transepithelial acid-base flux. Moreover, one must consider the influence of resident macrophages on AVSF pH. Resident macrophages occupy a sizable fraction of AVSF by volume and are a substantial source of metabolic H+. The buffering capacities of ASL and AVSF probably are largely due to secreted peptides (e.g., ASL mucins and AVSF surfactant proteins). Acid-base exchange between the extracellular hydrophase and intracellular buffering systems of resident macrophages represents an additional buffer pool for AVSF. The pH of ASL and AVSF can be depressed by disease or inflammation. Low pH is predicted to suppress microbe clearance from the airways and alveoli, increase pathogen survival in both regions, and alter mediator release by resident macrophages and recruited leukocytes thereby increasing the propensity for bystander cell injury. Overall, ASL/AVSF pH is expected to be a major determinant of lung host defense responses.

R-Ras3/(M-Ras) is involved in thermal adaptation in the critical period of thermal control establishment

Neuroanatomically, the body temperature is balanced by the preoptic anterior hypothalamus (PO/AH) and controlled by thermosensitive neurons. Hot or cold exposure during the critical period of temperature control development causes a plastic change in the ratio between hot- and cold-sensitive cells and can modulate temperature tolerance. In this project, mRNA fingerprinting was used to identify the proteins involved in thermal adaptation in 3-day-old chicks. Fifteen genes were induced, among which were NADH dehydrogenase, protocadherin, anolase alpha, 14-3-3epsilon, and R-Ras3. The role of each of these genes is potentially interesting and requires detailed evaluation, but since the present working hypothesis assumed neuronal remodeling, we concentrated on the role of R-Ras3/(M-Ras), which is uniquely expressed in the brain and whose physiological role has not been described. In the present study, R-Ras3 expression during thermal conditioning was investigated by several molecular techniques and its mRNA was found to be induced in the PO/AH with a tenfold peak after 12 h of heat conditioning and a fourfold increase after 6 h of cold conditioning. To improve our understanding of thermal adaptation-related signal transduction, we screened for changes in the expression of transcription factors that were implicated with the Ras gene family, and found that both jun mRNA expression and Jun phosphorylation were induced after 30 min of temperature conditioning. Taken together, the present findings correlate the R-Ras3-jun pathway with thermal-control establishment.

Plasmalemmal vacuolar H+-ATPase is decreased in microvascular endothelial cells from a diabetic model

Angiogenesis requires invasion of extracellular matrix (ECM) proteins by endothelial cells and occurs in hypoxic and acidic environments that are not conducive for cell growth and survival. We hypothesize that angiogenic cells must exhibit a unique system to regulate their cytosolic pH in order to cope with these harsh conditions. The plasmalemmal vacuolar type H(+)-ATPase (pmV-ATPase) is used by cells exhibiting an invasive phenotype. Because angiogenesis is impaired in diabetes, we hypothesized that pmV-ATPase is decreased in microvascular endothelial cells from diabetic rats. The in vitro angiogenesis assays demonstrated that endothelial cells were unable to form capillary-like structures in diabetes. The proton fluxes were slower in cells from diabetic than normal model, regardless of the presence or absence of Na(+) and HCO(3) (-) and were suppressed by V-H(+)-ATPase inhibitors. Immunocytochemical data revealed that pmV-ATPases were inconspicuous at the plasma membrane of cells from diabetic whereas in normal cells were prominent. The pmV-ATPase activity was lower in cells from diabetic than normal models. Inhibition of V-H(+)-ATPase suppresses invasion/migration of normal cells, but have minor effects in cells from diabetic models. These novel observations suggest that the angiogenic abnormalities in diabetes involve a decrease in pmV-ATPase in microvascular endothelial cells.

Effects of plasmalemmal V-ATPase activity on plasma membrane potential of resident alveolar macrophages

The acid-base status and functional responses of alveolar macrophages (mphi) are influenced by the activity of plasmalemmal V-type H+-pump (V-ATPase), an electrogenic H+ extruder that provides a possible link between intracellular pH (pHi) and plasma membrane potential (Em). This study examined the relationships among Em, pHi, and plasmalemmal V-ATPase activity in resident alveolar mphi from rabbits. Em and pHi were measured using fluorescent probes. Em was -46 mV and pHi was 7.14 at an extracellular pH (pHo) of 7.4. The pHi declined progressively at lower pHo values. Decrements in pHo, also caused depolarization of the plasma membrane, independent of V-ATPase activity. The pH effects on Em were sensitive to external K+, and hence, probably involved pH-sensitive K+ conductance. H+ were not distributed at equilibrium across the plasma membrane. V-ATPase activity was a major determinant of the transmembrane H+ disequilibrium. Pump inhibition with bafilomycin A1 caused cytosolic acidification, due most likely to the retention of metabolically generated H+. V-ATPase inhibition also caused depolarization of the plasma membrane, but the effects were mediated indirectly via the accompanying pHi changes. V-ATPase activity was sensitive to Em. Em hyperpolarization (valinomycin-clamp) reduced V-ATPase activity, causing an acidic shift in baseline pHi under steady-state conditions and slowing pHi recovery from NH4Cl prepulse acid-loads. The findings indicate that a complex relationship exists among Em, pHi, and pHo that was partially mediated by plasmalemmal V-ATPase activity. This relationship could have important consequences for the expression of pH- and/or voltage-sensitive functions in alveolar mphi.

Intracellular pH regulation in U937 human monocytes: roles of V-ATPase and Na+/H+ exchange

The role of plasmalemmal V-type H+ translocating ATPase (V-ATPase) in regulation of intracellular pH (pHi) is unclear in monocytes. This study examined the plasmalemmal V-ATPase and Na+/H+ exchanger (NHE) in U937 human monocytes. The fluorescent probe 2',7'-biscarboxyethyl-5,6-carboxyfluorescein was used to monitor baseline pHi and the kinetics of pHi recovery from cytosolic acid-loads (NH4Cl prepulse). Bafilomycin A1 and 5-(N-ethyl-N-isopropyl)amiloride (EIPA) were used to delineate the activities of the H+-pump and NHE, respectively. Baseline pHi was approximately 7.13 at an extracellular pH (pHo) of 7.4 and fell progressively at lower pHo values. EIPA had no effect on baseline pHi at pHo 7.4, but caused a sustained decrement in pHi at pHo 6.0-7.0. Bafilomycin A1 had biphasic effects on baseline pHi at pHo 6.5-7.4; pHi declined approximately 0.1 units over the course of several minutes and then recovered. At pHo 6.0, bafilomycin A1 caused a sustained decrement in baseline pHi. Recovery from the bafilomycin-induced acidosis at pHo 6.5-7.4 was prevented by EIPA. Similarly, pHi recovery from NH4Cl prepulse acid-loads (pHo 7.4) was sensitive to both EIPA and bafilomycin A1. During this recovery process, Na+/H+ exchange (EIPA-sensitive component of apparent H+ efflux) was the predominant mechanism for H+ extrusion at acid-loaded pHi values < 7.0. At acid-loaded pHi values > or = 7.0, the V-ATPase (bafilomycin-sensitive component) and NHE contributed almost equally to H+ extrusion. The data provide the first evidence that plasmalemmal V-ATPase participates in pHi regulation in U937 cells. The H+-pump and NHE interacted to set baseline pHi and for pHi recovery following cytosolic acid-loading of the monocytes.

Plasmalemmal H+ extruders in mammalian alveolar macrophages

The distribution of plasmalemmal V-type H+-pumps (V-ATPase) among mammalian macrophages (mvarphi) is uncertain and, hence, the functional significance of mvarphi plasmalemmal V-ATPase is unclear. This study investigated the role of V-ATPase in the regulation of intracellular pH (pH(i)) by resident alveolar mvarphi from sheep, pigs, dogs and rabbits. The fluorescent probe 2',7'-biscarboxyethyl-5,6-carboxyfluorescein was used to monitor baseline pH(i) and the rate of pH(i) recovery (dpH(i)/dt) from intracellular acid-loads (NH(4)Cl prepulse). Baseline pH(i) was 7.1-7.2. In sheep, pig and dog studies, 10 microM bafilomycin A(1) (a selective V-ATPase inhibitor) caused a rapid fall in baseline pH(i) (0.15-0.20 units); baseline values were unaffected by 0.1 mM amiloride (a Na+ transport inhibitor). V-ATPase activity (bafilomycin-sensitive component of dpH(i)/dt) was solely responsible for pH(i) recovery from intracellular acid-loads at acid-loaded pH(i) values >6.8-6.9. Na+/H+ exchange (amiloride-sensitive component of dpH(i)/dt) was detected only at acid-loaded pH(i) values <6.8. The activity of both H+ extruders increased at lower pH(i) values, albeit the Na+/H+ exchanger was more pH-sensitive than was V-ATPase. In rabbit studies, 10 microM bafilomycin A(1) and 1 mM N-ethylmaleimide (a non-specific H+-pump inhibitor) produced similar falls in baseline mvarphi pH(i), but had significantly larger effects than did the selective V-ATPase inhibitor concanamycin A (<or=15 microM). The findings suggest that plasmalemmal V-ATPase activity plays a major role in pH(i) regulation by alveolar mvarphi of sheep, pigs, dogs and rabbits.

Propranolol decreases splanchnic triacylglycerol storage in burn patients receiving a high-carbohydrate diet

OBJECTIVE

To quantify the various components of splanchnic free fatty acid and very-low-density lipoprotein-triacylglycerol (VLDL-TAG) metabolism in order to gain insight into the mechanisms responsible for the development of fatty liver in severely burned patients, and to determine if decreasing free fatty acid availability by use of propranolol could potentially reduce hepatic fatty acid accumulation.

SUMMARY BACKGROUND DATA

Hepatic fat accumulation results from an imbalance between fatty acid uptake, oxidation, and release via VLDL-TAG. Fatty acid delivery is accelerated in burn patients because of stimulated lipolysis. Since propranolol decreases lipolysis, it should also decrease hepatic fatty acid uptake and thus TAG synthesis.

METHODS

Stable isotope-labeled tracers and regional catheterization enabled quantification of various parameters of lipid metabolism across the splanchnic bed in severely burned patients. The acute effects of propranolol treatment were studied in all patients, and in a subgroup of patients the chronic (3 weeks) effects of propranolol were assessed.

RESULTS

The rate of splanchnic uptake of palmitate was 1.68 +/- 1.3 micromol/kg/min, whereas the rates of oxidation and VLDL-TG secretion were only 0.12 +/- 0.11 and 0.003 +/- 0.02 micromol/kg/min, respectively. Propranolol significantly reduced palmitate delivery, and thus palmitate uptake, without significantly affecting oxidation or VLDL-TAG secretion. Thus, palmitate storage was reduced from 1.53 +/- 1.30 micromol/kg/min without propranolol to 0.76 +/- 0.58 micromol/kg/min after propranolol.

CONCLUSIONS

Hepatic fat storage in burn patients is due to low rates of both fatty acid oxidation and VLDL-TAG secretion. Propranolol can decrease hepatic fat storage by limiting fatty acid delivery.

Characteristics of lysophosphatidylcholine in its inhibition of taurine uptake by human intestinal Caco-2 cells

The characteristics of lysophosphatidylcholine (LPC) in its inhibition of the taurine uptake by human intestinal Caco-2 cells were investigated. By treating the cells with 200 microM of LPC, the taurine uptake was rapidly decreased by approximately 60%. This decrease was accompanied by an increase in the Km value for the uptake. A rapid uptake of LPC itself by the cells was also observed. The inhibitory activity of LPC was specific to the uptake of taurine and certain amino acids, while the uptake of glucose, glutamic acid and peptide (glycylglutamine) was not affected by LPC. The activity was dependent on the structure of a polar head and the bound fatty acid. The phosphorylcholine residue was likely to have played an important role, and surface active LPC with fatty acids of C14 or longer was highly inhibitory. These results suggest that the interaction of LPC with the taurine transporter in the intestinal cell membrane was the cause of the reduced taurine uptake.

Protein turnover, lipolysis, and endogenous hormonal secretion in critically ill children

OBJECTIVES

The catabolic state is a major contributor to morbidity and mortality of critical illness and may be related to endocrine changes. We studied whether protein and lipid turnover correlate with insulin and growth and thyroid hormone plasma levels in critically ill infants.

DESIGN

Prospective clinical study.

SETTING

Pediatric intensive care unit.

PATIENTS

Twelve critically ill children and ten age-matched controls.

MEASUREMENTS

We measured lipolysis and protein turnover by infusing albumin-bound uniformly 13C palmitic acid and 2H3-leucine for 3 hrs and 2H5-glycerol for 5 hrs to critically ill infants. Simultaneously, we measured serum growth hormones, insulin, C-peptide, thyroid-stimulating hormone, T4, T3, albumin, retinol binding protein (RBP), and prealbumin. Hormone and serum protein levels were also measured in six children when recovered from critical illness. Ten healthy age-matched children served as controls for hormone serum levels comparison.

RESULTS

Palmitic acid and glycerol turnover were 5.6 +/- 2.2 micromol/kg/min and 12.2 +/- 7.3 micromol/kg/min, respectively, whereas alpha-ketoisocaproic turnover was 4.9 +/- 2.8 micromol/kg/min. Alpha-ketoisocaproic turnover positively correlated (R = 0.7, p = .03) with duration of pediatric intensive care unit admission and with prealbumin and RBP serum levels (R = 0.9, p = .001). Insulin-like growth factor binding protein (IGFBP)-2 was significantly higher and IGFBP-3 was significantly lower in critically ill children (p = .03 and p = .04 vs. recovery phase, respectively). No other hormonal differences were found. Serum albumin was significantly lower in sick children. We found a significant correlation between prealbumin and RBP and IGFBP-3 (R = 0.6, p = 0.03 and R = 0.6, p = .04, respectively). Alpha-ketoisocaproic turnover positively correlated with IGFBP-1 (R = 0.79, p = .01) and did not correlate with insulin-like growth factor I (R = -0.5, p = .15 [not significant]) No other correlations were found. Lipid turnover measurements did not correlate with any endogenous hormone levels or with duration of critical illness.

CONCLUSION

Protein turnover but not lipolysis correlated with a persisting critically ill condition, serum prealbumin, RBP, and plasma IGFBP-1.

pH(i) responses to osmotic cell shrinkage in the presence of open-system buffers

Changes in plasma volume in vivo cause rapid changes in extracellular pH by altering the plasma bicarbonate concentration at a constant Pco(2) (Garella S, Chang BS, and Kahn SI. Kidney Int 8: 279, 1975). Few studies have examined the possibility that changes in cell volume produce comparable changes in intracellular pH (pH(i)). In the present study, alveolar macrophages were exposed to hyperosmotic medium in the absence or presence of the open-system buffers CO(2)-HCO(3)(-), propionic acid-propionate, or NH(3)-NH(4)(+). In the absence of open-system buffers, exposure to twice-normal osmolarity (2T) produced a slow cellular alkalinization [change in pH(i) (DeltapH(i)) approximately 0.38; exponential time constant (tau) approximately 120 s]. In the presence of 5% CO(2), 2T caused a biphasic pH(i) response: a rapid increase (DeltapH(i) approximately 0.10, tau approximately 15 s) followed by a slower pH(i) increase. Identical rapid pH(i) increases were produced by 2T in the presence of propionic acid (20 mM). Conversely, 2T caused a rapid pH(i) decrease (DeltapH(i) approximately -0.21, tau approximately 10 s) in the presence of NH(3) (20 mM). Thus osmotic cell shrinkage caused rapid pH(i) changes of opposite direction in the presence of a weak acid buffer (contraction alkalosis with CO(2) or propionic acid) vs. a weak base buffer (contraction acidosis with NH(3)). Graded DeltapH(i) were produced by varying extracellular osmolarity in the presence of open-system buffers; osmolarity increases of as little as 5-10% produced significant DeltapH(i). The rapid pH(i) responses to 2T were insensitive to inhibitors of membrane H(+) transport (ethylisopropylamiloride and bafilomycin A(1)). The results are consistent with shrinkage-induced disequilibria in the total cellular buffer system (i.e., intrinsic buffers plus added weak acid-base buffer).

Identification of a taurine transport inhibitory substance in sesame seeds

An ethanol extract from sesame seeds inhibited the taurine uptake in human intestinal epithelial Caco-2 cells. The uptake of such alpha-amino acids as leucine and glutamic acid was not inhibited by the extract, indicating that this inhibition is specific to the taurine uptake. The unknown inhibitor in the sesame extract was purifled by reversed-phase HPLC by monitoring the inhibitory effect on taurine uptake. The isolated substance was identified as lysophosphatidylcholine, linoleoyl (Lyso-PC), by NMR and MS analysis. Lyso-PC inhibited the taurine uptake in a dose-dependent manner with an IC50 value of approximately 200 microM. Although Lyso-PC is known to be a surface active and cell lytic compound, neither damage nor loss of integrity of the Caco2 cell monolayer was apparent after treating with 200 microM Lyso-PC. Inhibition was observed by incubating cells with Lyso-PC for only 1 min prior to the uptake experiments. These results suggest the direct effect of Lyso-PC on the cell membrane to be the main mechanism for this inhibition. Lyso-PC may play a role in the regulation of certain intestinal transporters.

Cytokine production by rabbit alveolar macrophages: differences between activated and suppressor cell phenotypes

The differences between cytokine-producing profiles of activated macrophages (A-M phi) and suppressor macrophages (S-M phi) were examined. A-M phi, which exhibited cytotoxicity against RK-13 cells, were generated from resident rabbit alveolar M phi by treatment with lymphokine solution (culture fluids of rabbit spleen cells stimulated with concanavalin A [Con A]). S-M phi, which were able to inhibit cellular proliferations of rabbit spleen cells stimulated with Con A, were generated from resident alveolar M phi by treatment with 1-methyladenosine (an immunosuppressive molecule in tumourous ascites fluids). When A-M phi were stimulated with lipopolysaccharide (LPS) in vitro, the cells produced significantly more interleukin (IL)-1 (approximately 1.4 times), IL-6 (approximately 2.1 times), IL-12 (approximately 60 times), and tumour necrosis factor-alpha (TNF-alpha) (approximately 37 times) than did resting macrophages (R-M phi) stimulated with LPS as control cells. After the stimulation with LPS, both A-M phi and R-M phi did not produce transforming growth factor-beta (TGF-beta). In contrast, when S-M phi were stimulated with LPS in vitro, the cells produced significantly more TGF-beta (approximately 1.6 times) and significantly less IL-6 (approximately 1.8 times) than did control cells. Also, S-M phi did not produce IL-1, IL-12, and TNF-alpha into their culture fluids after the stimulation with LPS. These results show the differences between cytokine-producing profiles of A-M phi and S-M phi, and characteristics of their cytokine-producing profiles are analogous to T cell subsets. Differences displayed in the cytokine profiles may contribute to the effector (A-M phi) or the suppressor (S-M phi) functions of alveolar M phi.

Regulation of fatty acid oxidation in skeletal muscle

Researchers using animals are beginning to elucidate the control of fatty acid metabolism in muscle at the molecular and enzymatic level. This review examines the physiological data that has been collected from human subjects in the context of the proposed control mechanisms. A number of factors, including the availability of free fatty acids and the abundance of fatty acid transporters, may influence the rate of muscle fatty acid oxidation. However, the predominant point of control appears to be the rate at which fatty acyl-coenzyme A is transported into the mitochondria by the carnitine palmitoyl transferase system. In turn, evidence suggests that the intracellular concentration of malonyl-coenzyme A in muscle is an important regulator of carnitine palmitoyl transferase-I activity. Malonyl-coenzyme A is increased by glucose, which is likely the mechanism whereby glucose intake suppresses the transfer of fatty acids into the mitochondria for subsequent oxidation. In contrast, malonyl-coenzyme A levels decrease during exercise, which enables increased fatty acid oxidation. However, for any given carnitine palmitoyl transferase-I activity, there may be an effect of free fatty acid availability on fatty acid oxidation, particularly at low levels of free fatty acids. Nonetheless, the rate of glucose or glycogen metabolism is probably the primary regulator of the balance between glucose and fatty acid oxidation in muscle.

Regulation of intracellular pH in hamster preimplantation embryos by the sodium hydrogen (Na+/H+) antiporter

This study was an investigation of the mechanisms for the regulation of intracellular pH (pHi) by hamster preimplantation embryos. The resting pH values of hamster embryos were similar at the 1-cell (7. 19 +/- 0.34), 2-cell (7.21 +/- 0.21), and 8-cell (7.22 +/- 0.41) stages. Cleavage-stage hamster embryos alleviated intracellular acidosis by activity of the Na+/H+ antiporter. The rate of recovery from acidosis was similar for embryos at 1-cell, 2-cell, and 8-cell stages. When Na+/H+ antiporter activity was inhibited by either incubation in Na+-free medium or the presence of an inhibitor, pHi was unable to recover to initial levels. Instead, pHi remained acidic. The Na+/H+ antiporter was also found to contribute to baseline pH regulation, as incubation in Na+-free medium resulted in an immediate intracellular acidification. The set point for Na+/H+ antiporter was pH 7.14. There was no evidence at any developmental stage for activity of either Na+-dependent HCO3-/Cl- exchanger or H+-ATPase in the regulation of pHi. Inhibition of the Na+/H+ antiporter by an amiloride derivative significantly reduced the ability of 2-cell embryos to develop in culture when challenged with acidosis, indicating that the Na+/H+ antiporter is an essential regulator of pHi.

Molecular biology of mammalian plasma membrane amino acid transporters

Molecular biology entered the field of mammalian amino acid transporters in 1990-1991 with the cloning of the first GABA and cationic amino acid transporters. Since then, cDNA have been isolated for more than 20 mammalian amino acid transporters. All of them belong to four protein families. Here we describe the tissue expression, transport characteristics, structure-function relationship, and the putative physiological roles of these transporters. Wherever possible, the ascription of these transporters to known amino acid transport systems is suggested. Significant contributions have been made to the molecular biology of amino acid transport in mammals in the last 3 years, such as the construction of knockouts for the CAT-1 cationic amino acid transporter and the EAAT2 and EAAT3 glutamate transporters, as well as a growing number of studies aimed to elucidate the structure-function relationship of the amino acid transporter. In addition, the first gene (rBAT) responsible for an inherited disease of amino acid transport (cystinuria) has been identified. Identifying the molecular structure of amino acid transport systems of high physiological relevance (e.g., system A, L, N, and x(c)- and of the genes responsible for other aminoacidurias as well as revealing the key molecular mechanisms of the amino acid transporters are the main challenges of the future in this field.

Hypothalamic neurons. Mechanisms of sensitivity to temperature

Rostral hypothalamic neurons are influenced by endogenous factors that affect thermoregulation and fever. Intracellular recordings reveal the synaptic and intrinsic mechanisms responsible for neuronal thermosensitivity. Many temperature-sensitive and temperature-insensitive neurons display a depolarizing prepotential that precedes action potentials. Temperature has little effect on the prepotential of insensitive neurons; however, in warm-sensitive neurons, the prepotential's depolarization is elevated by warming, and this increases the firing rate. Intracellular cAMP can increase neuronal thermosensitivity by enhancing the thermal response of the prepotential, most likely by thermosensitive ionic conductances. Warm-sensitive neurons also receive inhibitory synaptic input (IPSPs) from temperature-insensitive neurons, enhancing the thermosensitivity of some neurons, because cooling increases IPSP amplitude and duration. Therefore, even though IPSP frequencies do not change, cooling can decrease firing rates by increasing IPSP amplitudes. Because endogenous factors change neuronal firing rate and thermosensitivity, these changes likely occur both post- and presynaptically as well as by ionic conductances that determine the time interval between action potentials.

A proton-translocating H+-ATPase is involved in C6 glial pH regulation

Glial cells extrude acid equivalents to maintain pHi. Although four mechanisms have been described so far, pHi-control under physiological conditions is still not sufficiently explained. We therefore investigated whether a H+-translocating ATPase is involved in glial pHi homeostasis using an established glial cell line (C6 glioma). In the absence of bicarbonate, the inhibition of H+-ATPases by NEM led to a pHi decrease. The application of a more specific inhibitor (NBD-Cl) showed that the H+-ATPase involved is of the vacuolar type. Inhibition went along with delayed cell swelling. Together with the fact that glial acidification was far more pronounced in Na+-free media, this may serve as evidence for a secondary activation of Na+/H+-exchange once an activation setpoint is reached, which in turn causes secondary swelling from Na+-uptake. Stimulation of Na+/H+-exchange by PMA can increase the setpoint. pHi-recovery after an acid load was blocked by the inhibition of v-type H+-ATPase, if pHi did not reach 6.6 during the acid load. The inhibition of Na+/H+-exchange by amiloride inhibited recovery only if acidification was below the threshold. Finally, in bicarbonate-free media a v-type H+-ATPase contributes to pH-regulation in glial cells, especially during pH-homeostasis at physiological conditions, while Na+/H+-exchange gains significance during severe acid loads.

Functional expression of a vacuolar-type H+-ATPase in the plasma membrane and intracellular vacuoles of Trypanosoma cruzi

Acid-loaded Trypanosoma cruzi amastigotes and trypomastigotes regained normal cytoplasmic pH (pHi), as measured in cells loaded with 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF), by a process that was sensitive to bafilomycin A1 at concentrations comparable to those that inhibited vacuolar (V) H+-ATPases from different sources. Steady-state pHi was also decreased by similar concentrations of bafilomycin A1 in a concentration-dependent manner. The efflux of H+ equivalents from amastigotes and trypomastigotes was measured by following changes in the fluorescence of extracellular BCECF. Basal H+ extrusion in the presence of glucose was 15.4+/-2.8 (S.D.) nmol of H+/min per 10(8) amastigotes and 6. 37+/-0.8 nmol of H+/min per 10(8) trypomastigotes. Bafilomycin A1 treatment significantly decreased the efflux of H+ equivalents by amastigotes (8.9+/-2.2 nmol of H+/min per 10(8) cells), but not by trypomastigotes (5.1+/-1.7 nmol of H+/min per 10(8) cells). The localization of the V-H+-ATPase of T. cruzi was investigated by immunocytochemistry. Confocal and electron microscopy indicated that, in addition to being located in cytoplasmic vacuoles, the V-H+-ATPase of different stages of T. cruzi is also located in the plasma membrane. However, no labelling was detected in the plasma membrane lining the flagellar pocket of the different developmental stages. Surface localization of the V-H+-ATPase was confirmed by experiments involving the biotinylation of cell surface proteins and immunoprecipitation with antibodies against the V-H+-ATPase. Taken together, the results are consistent with the presence of a functional V-H+-ATPase in the plasma membrane of amastigotes and with an important role for intracellular acidic compartments in the maintenance of pHi in different stages of T. cruzi.

Calyculin A modulates the kinetic constants for the Na+-coupled taurine transport in Ehrlich ascites tumour cells

The effect of the phosphatase inhibitor calyculin A (cal A) on the kinetic parameters of the Na+-coupled taurine uptake via the taurine transporter in the Ehrlich ascites tumour cells has been investigated. Preincubation with cal A (100 nM) reduces the initial taurine influx by about 20%, but has no effect on the diffusional component of the taurine influx or on the taurine release from cells suspended in isotonic or in hypotonic medium. Thus, cal A-sensitive phosphatases only affect taurine transport mediated by the Na+-dependent taurine transporter. Cal A increases the Michaelis-Menten constant for binding of taurine to the transporter from 31+/-6 to 45+/-4 microM and reduces the taurine transport capacity from 210+/-20 to 170+/-10 nmol x g dry wt(-1) x min(-1) [corrected]. The Michaelis-Menten constant for binding of Na+ to the taurine transporter is concomitantly increased from 96+/-11 to 129+/-8 mM and the Na+:taurine coupling ratio for activation of the transport cycle is reduced from 3.3+/-0.6 to 2.4+/-0.2. This suggests that cal A-sensitive phosphatases maintain a high affinity of the taurine transporter towards Na+ and taurine as well as a high taurine transport capacity in unpertubated Ehrlich cells.

Metabolic alteration in patients with cancer: nutritional implications

During the past 20 years, efforts have been made to elucidate the metabolic changes observed in patients with cancer by using stable and radioactive isotopic tracers. These metabolic changes in patients with cancer may be similar to those in other stress conditions, in which glucose production and utilization, lipolysis and free fatty acid flux, and net protein catabolism are increased. Stress hormones, such as glucagon and catecholamines, and certain cytokines may be responsible for these metabolic changes. Although it has been shown that cachexia in patients with cancer signals a poor prognosis, efforts to improve the clinical outcomes with nutritional support have been disappointing. The failure of cancer patients to respond to nutritional support may be related to an alteration in the intermediate metabolism. Therefore, further research evaluating the metabolic abnormalities associated with cancer may lead to more effective nutritional therapies.

Spectral pathology

We are investigating the use of optical spectroscopy (fluorescence, reflectance, Raman scattering) for detecting precancerous lesions in the mucosal linings of hollow organs. We present a morphological model for extracting quantitative pathological information from fluorescence spectra, using colonic dysplasia as an example. The potential of this technique in providing histological information in real time without the need for tissue removal is discussed.

Glutathione S-transferases of rabbit lung macrophages

The catalytic activities of glutathione S-transferases (GSTs), particularly the alpha-class isozymes, can provide protection against oxidative stress through GSH-mediated metabolism of reactive products of lipid peroxidation. Lipid peroxidation products from oxidative metabolism in alveolar macrophages play an important role in mediating and regulating inflammatory response and injury in the lung. The rabbit has been used as an important animal model for studies of the role of alveolar macrophages in pulmonary pathology. Although rabbit lung macrophages display GST activity, the isozyme-specific expression of GSTs and the catalytic properties of these isozymes has not previously been defined. In present studies, we have purified the GST isozymes of rabbit alveolar macrophages obtained by bronchoalveolar lavage and performed immunologic and kinetic characterization of the purified isozymes. Results of our studies indicate the presence of three alpha-class isozymes (pI 10.2, 9.3, and 6.0) and one micro-class isozyme (pI 7.2). N-terminal sequence analysis of the micro-class isozyme indicated that it was distinct from the two previously described micro-class isozymes of rabbit. Kinetic studies indicated that two cationic alpha-class GSTs (pI 10.2 and 9.3) contribute the large majority of selenium independent GSH-peroxidase activity toward dilinoleoyl phosphatidylcholine hydroperoxide (kcat/Km values of 83.4 and 31.9 s-1 . M-1 . 10(3), respectively). A third alpha-class GST (pI 6.0) was shown to have highest catalytic activity toward conjugation of the 4-hydroxynonenal (4HNE) with GSH (kcat/Km = 1900 s-1 . M-1 . 10(3)). Structural and immunologic characterization of this GST isozyme indicated that it belongs to a subclass of the alpha-classGSTs selectively expressed in mesodermal origin cells that are exposed to high levels of oxidative stress and are characterized by high specific activity toward both lipid hydroperoxides and 4-HNE.

Osteoclast activation: potent inhibition by the bisphosphonate alendronate through a nonresorptive mechanism

Alendronate, an aminobisphosphonate used in the treatment of osteoporosis, is a potent inhibitor of bone resorption. Its mechanism of action is unknown. Because it localizes to bone surfaces, we compared the sensitivity of components of the resorptive process to incubation on alendronate-coated bone surfaces. We found that bone resorption by osteoclasts isolated from neonatal rat bone was unaffected by alendronate (10(-4) M). Osteoclast production in bone marrow cultures, as assessed by the production of calcitonin-receptor positive cells, was observed even at 10(-4) M, but bone resorption in these cultures was almost completely abolished by 10(-5) M alendronate. The greater sensitivity of osteoclast activation to inhibition by alendronate that these results suggest was supported by similar inhibition of osteoblast-mediated activation of osteoclasts from neonatal rat bone. Thus, activation of osteoclasts by osteoblastic/stromal cells is apparently the most sensitive component of the pathway whereby bone resorption is affected. Moreover, the ability of alendronate to suppress osteoclastic activation does not depend on resorption-mediated release of alendronate from bone surfaces. This ability extends the range of cell types and processes that might be affected by alendronate, beyond those in the immediate vicinity of resorbing cells, to include any cell that comes into contact with alendronate-coated bone surfaces.

Influence of alkaline buffers on cytoplasmic pH in myocardial cells exposed to hypoxia

The fluorescent intracellular probe 2',7'-bis-(carboxyethyl)-5,6-carboxyfluorescein acetoxymethyl ester was used in this experimental study to investigate the effects of different alkaline buffers on cytoplasmic pH in suspended myocardial cells under normal as well as hypoxic conditions. A dose-dependent intracellular acidification was achieved after addition of sodium bicarbonate or Tris buffer mixture (Tribonat) to the myocardial cells under normal conditions. After this immediate decrease in cytoplasmic pH, a tendency for the pH to rise again was recorded during the observation period, but this elevation of pH occurred to variable degrees with the different agents and dosages. Addition of larger volumes of Tribonat caused the cytoplasmic pH to return to the initial value during the observation time. Addition of Ringer's acetate produced a significant and persistent cytoplasmic acidification. Larger volumes of Carbicarb as well as pure trometamol (Tris) caused a lasting intracellular alkalinization. Hypoxia per se caused a marked intracellular acidosis in the cardiomyocytes. During hypoxia, addition of sodium bicarbonate caused a further decrease of cytoplasmic pH, turning into an increase during the observation period. Also, Tribonat caused an immediate further acidification, but 15 min after the addition the intracellular pH-value had reached the normal level of normoxic cells. Addition of Ringer's acetate caused a further significant and lasting decrease of intracellular pH. The effect of Carbicarb was a persistent alkalinization of the cell interior. Trometamol produced the most pronounced rise of cytoplasmic pH. In conclusion, this in vitro study shows that Tris buffer mixture (Tribonat) possesses important qualities for correction of metabolic acidosis due to hypoxia and may perhaps be preferred over other alkaline buffers in some situations.

Interaction of taurine on baclofen intestinal absorption: a nonlinear mathematical treatment using differential equations to describe kinetic inhibition models

Previous studies showed that the in situ absorption of baclofen in rat jejunum was inhibited by beta-alanine, a nonessential amino acid, and therefore mediated, at least in part, by some beta-amino acid carrier. In this paper a similar study was undertaken using taurine, a sulfonic beta-amino acid, in order to evaluate its effect and to establish a general inhibition model. To achieve this goal, remaining concentrations of inhibitor were also measured and incorporated into the model. Previously, kinetic absorption in situ parameters for taurine in free solution were obtained: Vm = 27.73 +/- 9.99 mM h-1, K(m) = 8.06 +/- 2.82 mM, Ka (passive difussion component) = 0.40 +/- 0.28 h-1. Isotonic solutions containing 0.5 mM baclofen with starting taurine concentrations ranging from 0 to 100 mM were perfused in rat jejunum, and the remaining concentrations of both compounds were measured. The apparent rate pseudoconstant of the drug clearly decreased as the remaining taurine concentration increased. The interaction can be described as a complete competitive inhibition plus a second component, K, noninhibited, K = 0.58 (+/- 0.03) h-1, Ki = 20.62 (+/- 4.04) mM, Vmi = 28.12 (+/- 6.12) mM h-1, Kmi = 11.71 (+/- 2.53) mM, Kai = 0.47 (+/- 0.10) h-1. A residual absorption of baclofen in the presence of high taurine concentrations was observed, which should be attributed to another transport system not associated with the taurine carrier. In order to elucidate whether or not taurine and beta-alanine carriers are two separate entities that baclofen can use for absorption, further experiments using beta-alanine and taurine together as inhibitors (baclofen, 0.5 mM; beta-alanine, 50 mM, and taurine, 50 mM) were developed. Results indicated that baclofen and both amino acids share the same carrier in the intestinal absorption process. We have completed studies using leucine, taurine, and GABA together as inhibitors of drug absorption. An isotonic perfusion solution of 0.5 mM baclofen in the presence of 50 mM leucine, 25 mM taurine, and 25 mM GABA was perfused. Under these conditions the absorption rate pseudoconstant of baclofen decreases until 0.080 h-1 (+/- 0.069). Practical implications of these phenomena are briefly discussed.

Increased production of PDGF by angiotensin and high glucose in human vascular endothelium

The mechanisms responsible for the abnormalities in the vascular wall associated with long standing diabetes mellitus are incompletely understood. The aim of this investigation was to assess the effects of angiotensin II and high glucose on the production of platelet-derived growth factor (PDGF) in human endothelial cells. For this purpose, a primary culture was obtained from fresh human umbilical cords by collagenase digestion of the vein interior. A high glucose medium increased the production of PDGF and a similar effect was observed by the addition of mannitol. These data are consistent with a stimulatory effect of glucose on PDGF that is mediated by the osmotic effect of this substance. Angiotensin II significantly increased PDGF in human endothelial cells and the effect was accompanied by a transient increase in cytosolic calcium. The angiotensin II-induced intracellular Ca2+ increases, PDGF production were completely abolished by saralasin and neomycin, respectively. We postulate that the increased production of PDGF by the vascular endothelium in response to high glucose and angiotensin II may participate in the development of the diabetic angiopathy.