bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cytoplasmic and mitochondrial Ca2+ levels in brown adipocytes
Authors: Nakagaki I. , Sasaki S. , Yahata T. , Takasaki H. , Hori S. 
Published: January 2005

AbstractAim:  We elucidated the mitochondrial functions of brown adipocytes in intracellular signalling, paying attention to mitochondrial activity and noradrenaline‐ and forskolin‐induced Ca2+ mobilizations in cold‐acclimated rats.Methods:  A confocal laser‐scanning microscope of brown adipocytes from warm‐ or cold‐acclimated rats was employed using probes rhodamine 123 which is a mitochondria‐specific cationic dye, and the cytoplasmic and mitochondrial Ca2+ probes fluo‐3 and rhod‐2. X‐ray microanalysis was also studied.Results:  The signal of rhodamine 123 in the cells was decreased by antimycin A which effect was less in cold‐acclimated cells than warm‐acclimated cells. Cytoplasmic and mitochondrial Ca2+ in cold‐acclimated brown adipocytes double‐loaded with fluo‐3 and rhod‐2 were measured. Noradrenaline induced the rise in cytoplasmic Ca2+ ([Ca2+]cyto) followed by mitochondrial Ca2+ ([Ca2+]mito), the effect being transformed into an increase in [Ca2+]cyto whereas a decrease in [Ca2+]mito by antimycin A or carbonyl cyanide m‐chlorophenylhydrazone (CCCP). Antimycin A induced small Ca2+ release from mitochondria. CCCP induced Ca2+ release from mitochondria only after the cells were stimulated with noradrenaline. Further, forskolin also elicited an elevation in [Ca2+]cyto followed by [Ca2+]mito in the cells. The Ca measured by X‐ray microanalysis was higher both in the cytoplasm and mitochondria whereas K was higher in the mitochondria of cold‐acclimated cells in comparison to warm‐acclimated cells.Conclusions:  These results suggest that noradrenaline and forskolin evoked an elevation in [Ca2+]cyto followed by [Ca2+]mito, in which H+ gradient across the inner membrane is responsible for the accumulation of calcium on mitochondria. Moreover, cAMP also plays a role in intracellular and mitochondrial Ca2+ signalling in cold‐acclimated brown adipocytes.
Local cold acclimation of the hand impairs thermal responses of the finger without improving hand neuromuscular function
Authors: Geurts C. L. M. , Sleivert G. G. , Cheung S. S. 
Published: January 2005

AbstractAim:  To investigate the effects of cold acclimation on the thermal response and neuromuscular function of the hand.Methods:  Ten healthy subjects [three female, seven male, age (mean ± SD): 27.9 ± 7.9 years] immersed their right hand in 8 °C water for 30 min, 5 days a week for 3 weeks. On the first and the last day, neuromuscular function of the first dorsal interosseus (FDI) muscle was tested.Results:  There was no significant change in maximal voluntary contraction strength or evoked contractile characteristics of the FDI after cold acclimation. Minimum finger temperature decreased significantly from 10.6 ± 1.2 to 9.3 ± 0.8 °C after 3 weeks (P < 0.01), with most of the decrease occurring after a single exposure. Mean finger temperature dropped significantly from 14.2 ± 1.9 to 11.7 ± 1.4 °C following cold acclimation (P < 0.05), with 90% of this adaptation occurring after 5 days. Onset time of cold‐induced vasodilatation increased from 446 ± 171 to 736 ± 384 s (P < 0.05) and the amplitude decreased from 5.3 ± 3.2 to 2.5 ± 2.1 °C (P < 0.05). This was significantly different from the control group, who immersed their right hand on the first and last days only.Conclusion:  These data suggest that cold acclimation does not enhance hand temperature or function but may put the hands at a greater risk of cold injury when exposed to the cold.
The acute effects of insulin on the cardiorespiratory responses to hypoxia in streptozotocin‐induced diabetic rats
Authors: Saiki C. , Seki N. , Furuya H. , Matsumoto S. 
Published: January 2005

AbstractAims:  We examined whether or not streptozotocin (STZ)‐induced diabetic rats, which have a lower heart rate (HR, beats min−1) than control rats, could maintain hypoxic ventilatory response.Methods:  Twenty‐six Wistar rats, which had been injected with STZ (60 mg kg−1, EXP) or vehicle (0.1 m citrate buffer, CONT) intraperitoneally at 9 weeks of age, had their cardiorespiratory responses to normoxia and 12%O2 examined after 5 weeks.Results:  Compared with CONT rats, EXP rats had a higher blood glucose [24 ± 3 vs. 5 ± 1 (mean ± SD) mmol L−1], a lower body weight (320 ± 23 vs. 432 ± 24 g), lower HR (303 ± 49 vs. 380 ± 44 in normoxia, and 343 ± 56 vs. 443 ± 60 in hypoxia) and a lower mean arterial blood pressure (MAP) (89 ± 6 vs. 102 ± 10 mmHg in hypoxia). In contrast, both groups had similar values in ventilation (), –metabolic rate (MR) ratio and arterial blood gases (ABGs). In EXP rats, with an acute insulin supplement (i.v., 0.75 U h−1 for 1.5–2 h), not only blood glucose, but also HR, and MAP were normalized as those obtained in CONT rats, and in hypoxia further increased without affecting –MR ratio and ABGs. Such acute cardiorespiratory stimulating effects of insulin could not be obtained in non‐diabetic rats (n = 7, 355 ± 24 g), in which euglycaemia (mean 6.4 mmol L−1) was maintained during the measurements.Conclusions:  Our results suggest that, in STZ‐induced diabetic rats: (1) ventilation is hardly suppressed by hyperglycaemia, (2) cardiorespiratory responses can be acutely stimulated by short insulin injection, and (3) the effects, including those through acute blood glucose normalization, are possibly specific for the diabetic impairments.
Effects of renal nerve stimulation on intrarenal blood flow in rats with intact or inactivated NO synthases
Authors: Walkowska A. , Bądzyńska B. , Kompanowska‐Jezierska E. , Johns E. J. , Sadowski J. 
Published: January 2005

AbstractAim:  We studied a possible action of nitric oxide (NO), an intrarenal vasodilator, to buffer a decrease in renal perfusion induced by electrical stimulation of renal nerves (RNS).Methods:  In anaesthetized rats RNS was performed (15 V, 2 ms pulse duration) for 10 s at the frequencies of 2, 3.5, 5 and 7.5 Hz. The total renal blood flow (RBF), an index of cortical perfusion, was measured using a Transonic probe on the renal artery. The outer and inner medullary blood flow (OMBF, IMBF) was measured by laser‐Doppler flowmetry. The effect of RNS on RBF, OMBF and IMBF was determined in rats which were either untreated or pre‐treated with l‐NAME (0.6 or 1.8 mg kg−1 i.v.), or S‐methyl thiocitrulline (SMTC, 20 μg kg−1 min−1 i.v.), a selective inhibitor of neuronal NO synthase (nNOS).Results:  In untreated rats, RNS decreased IMBF significantly less than RBF and OMBF. High‐dose l‐NAME treatment significantly enhanced the RNS induced decrease of RBF but not of OMBF or IMBF. SMTC treatment significantly enhanced the decrease of IMBF, without affecting the response of RBF or OMBF.Conclusion:  At intact NO synthesis the inner medullary circulation is not controlled by renal nerves to the extent observed for the outer medulla or cortex. NO generated by all NOS isoforms present in the kidney buffers partly the intrarenal vasoconstriction triggered by electrical RNS. The NO derived from nNOS seems of particular importance in the control of inner medullary perfusion, interacting with NO generated by endothelial NOS and renal nerves.
Mechanisms regulating GLUT4 glucose transporter expression and glucose transport in skeletal muscle
Authors: Zorzano A. , Palacín M. , Gumà A. 
Published: January 2005

AbstractSkeletal muscle is a major glucose‐utilizing tissue in the absorptive state and the major glucose transporter expressed in muscle in adulthood is GLUT4. GLUT4 expression is exquisitely regulated in muscle and this seems important in the regulation of insulin‐stimulated glucose uptake by this tissues. Thus, muscle GLUT4 overexpression in transgenic animals ameliorates insulin resistance associated with obesity or diabetes. Recent information indicates that glut4 gene transcription is regulated by a number of factors in skeletal muscle that include MEF2, MyoD myogenic proteins, thyroid hormone receptors, Krüppel‐like factor KLF15, NF1, Olf‐1/Early B cell factor and GEF/HDBP1. In addition, studies in vivo indicate that under normal conditions the activity of the muscle‐specific GLUT4 enhancer is low in adult skeletal muscle compared with the maximal potential activity that it can attain at high levels of the MRF transcription factors, MEF2, and TRα1. This finding indicates that glut4 transcription may be greatly up‐regulated via activation of this enhancer through an increase in the levels of expression or activity of these transcription factors. Understanding the molecular basis of the expression of glut4 will be useful for the appropriate therapeutic design of treatments for insulin‐resistant states. The nature of the intracellular signals that mediate the stimulation of glucose transport in response to insulin or exercise is also reviewed.
Lipid metabolism in human skeletal muscle cells: effects of palmitate and chronic hyperglycaemia
Authors: Aas V. , Rokling‐Andersen M. , Wensaas A. J. , Thoresen G. H. , Kase E. T. , Rustan A. C. 
Published: January 2005

AbstractThis review focuses on the effect of exogenous factors known to be of importance for the development of insulin resistance in differentiated human myotubes. Recent data from our laboratory on the effects of fatty acid pre‐treatment and chronic glucose oversupply on fatty acid and glucose metabolism, without and with acute insulin are presented, and discussed in the context of other recent publications in the field. Pre‐treatment of myotubes with palmitate, chronic hyperglycaemia, and acute high concentrations of insulin changed fatty acid metabolism in favour of accumulation of intracellular lipids. Acute insulin exposure increased 14C‐oleate uptake and levels of free fatty acids (FFA) and triacylglycerol (TAG). Palmitate pre‐treatment further increased oleate uptake, both under basal conditions and in the presence of insulin, with a marked increase in the phospholipid (PL) fraction, with a concomitant reduction in oleate oxidation. Chronic hyperglycaemia also promoted increased lipogenesis and elevated levels of cellular lipids. Changes in fatty acid metabolism in human muscle, in particular fatty acid oxidation, are probably crucial for the molecular mechanism behind skeletal muscle insulin resistance and impaired glucose metabolism. Differentiated human skeletal muscle cells may be an ideal system to further explore the mechanisms regulating lipid metabolism.
Mechanisms regulating phosphoinositide 3‐kinase signalling in insulin‐sensitive tissues
Authors: Shepherd P. R. 
Published: January 2005

AbstractA great deal of evidence has accumulated indicating that the activity of PI 3‐kinase is necessary, and in some cases sufficient, for a wide range of insulin's actions in the cell. Most biochemical, genetic and pharmacological studies have focused on identifying potential roles for the class‐Ia PI 3‐kinases which are rapidly activated following insulin stimulation. However, recent evidence indicates the alpha isoform of class‐II PI 3‐kinase (PI3K‐C2α) may also play a role as insulin causes a very rapid activation of this as well. The basic mechanisms by which insulin activates the various members of the PI 3‐kinase family are increasingly well understood and these studies reveal multiple mechanisms for modulating the activity and functionality of PI 3‐kinase and for down regulating the signals they generate. These include inhibitory phosphorylation events, lipid phosphatases such as PTEN and SHIP2 and inhibitor proteins of the suppressors of cytokine signalling (SOCS) family. The current review will focus on these mechanisms and how defects in these might contribute to the development of insulin resistance.
Cellular mechanisms of insulin resistance, lipodystrophy and atherosclerosis induced by HIV protease inhibitors
Authors: Rudich A. , Ben‐Romano R. , Etzion S. , Bashan N. 
Published: January 2005

AbstractAccumulating clinical evidence now links HIV protease inhibitors (HPIs) to the pathogenesis of insulin resistance, dyslipidaemia, lipodystrophy and atherosclerosis associated with highly active anti‐retroviral therapy. Here we briefly describe the evidence for a distinct causative role for HPIs, and explore the cellular mechanisms proposed to underlie these side‐effects. Acute inhibition of GLUT4‐mediated glucose transport, and defective insulin signalling induced by chronic exposure to nelfinavir, are described as cellular mechanisms of insulin resistance. Interference with adipogenesis and adipocyte apoptosis and nelfinavir‐induced activation of lipolysis are discussed as potential mechanisms of HPI‐induced lipodystrophy. HPI‐induced free radical production, apoptosis and increased glucose utilization in vascular smooth muscle cells are presented as possible novel mechanisms for atherosclerosis. Common pathways and cause–effect relationships between the various cellular mechanisms presented are then discussed, with emphasis on the role of insulin resistance, free radical production and enhanced lipolysis. Understanding the cellular mechanisms of HPI‐induced side‐effects will enhance the search for improved anti‐retroviral therapy, and may also shed light on the pathogenesis of common forms of insulin resistance, dyslipidaemia and atherosclerosis.
The brown adipose cell: a model for understanding the molecular mechanisms of insulin resistance
Authors: Valverde A. M. , Benito M. , Lorenzo M. 
Published: January 2005

AbstractType 2 diabetes mellitus is a complex metabolic disease that occurs when insulin secretion can no longer compensate insulin resistance in peripheral tissues. At the molecular level, insulin resistance correlates with impaired insulin signalling. This review provides new insights into the molecular mechanisms of insulin action and resistance in brown adipose tissue and pinpoints the role of this tissue in the control of glucose homeostasis. Brown adipocytes are target cells for insulin and IGF‐I action, especially during late foetal development when insulin supports survival and promotes both adipogenic and thermogenic differentiation. The main pathway involved in insulin induction of adipogenic differentiation, monitored by fatty acid synthase expression, is the cascade insulin receptor substrate (IRS)‐1/phosphatidylinositol 3‐kinase (PI3K)/Akt. Glucose transport in these cells is maintained mainly by the activity of GLUT4. Acute insulin treatment stimulates glucose transport largely by mediating translocation of GLUT4 to the plasma membrane, involving the activation of IRS‐2/PI3K, and the downstream targets Akt and protein kinase C ζ. Tumour necrosis factor (TNF‐α) caused insulin resistance on glucose uptake by impairing insulin signalling at the level of IRS‐2. Activation of stress kinases and phosphatases by this cytokine contribute to insulin resistance. Furthermore, brown adipocytes are also target cells for rosiglitazone action since they show a high expression of peroxisome proliferator activated receptor γ, and rosiglitazone increased the expression of the thermogenic uncoupling protein 1. Rosiglitazone ameliorates insulin resistance provoked by TNF‐α, completely restoring insulin‐stimulated glucose uptake in parallel to the insulin signalling cascade. Accordingly, foetal brown adipocytes represent a model for investigating insulin action, as well as for the mechanism by which rosiglitazone increase insulin sensitivity under situations that mimic insulin resistance.
Regional differences of insulin action in adipose tissue: insights from in vivo and in vitro studies
Authors: Giorgino F. , Laviola L. , Eriksson J. W. 
Published: January 2005

AbstractAdipose tissue is now recognized to have a multitude of functions that are of importance in the regulation of energy balance and substrate metabolism. Different hormones, in particular insulin and catecholamines, govern the storage and utilization of energy in the triglyceride depots. In addition, adipocytes produce several different substances with endocrine or paracrine functions, which regulate the overall energetic homeostasis. With excess energy storage, obesity develops, leading to increased risk for type 2 diabetes and cardiovascular disease. The distribution of body fat appears to be even more important than the total amount of fat. Abdominal and, in particular, visceral adiposity is strongly linked to insulin resistance, type 2 diabetes, hypertension and dyslipidaemia, leading to increased risk of cardiovascular disease. The adverse metabolic impact of visceral fat has been attributed to distinct biological properties of adipocytes in this depot compared with other adipose tissue depots. Indeed, regional variations in the metabolic activity of fat cells have been observed. Furthermore, expression studies aiming at defining the unique biological properties of adipose tissues from distinct anatomical sites have identified depot‐related differences in the protein content of fat‐produced molecules. In this review we wish to summarize important results from the literature and also some recent data from our own work. The main scope is to describe the biological functions of adipose tissue, and to focus on metabolic, hormonal, and signalling differences between fat depots.
Production of interleukin (IL)-10 and IL-12 by murine colonic dendritic cells in response to microbial stimuli
Authors: Rigby R J , Knight S C , Kamm M A , Stagg A J 
Published: January 2005

SummaryIntestinal dendritic cells (DC) are likely to regulate immunity to gut microflora, but little is known about their responses to bacterial antigens. Therefore, DC from normal murine colon were characterized and their cytokine responses to components of Gram-negative and/or Gram-positive bacteria assessed. Cells were obtained by digestion of colonic tissue and contained DC that were identified by flow cytometry as CD11c+ major histocompatibility complex (MHC) class II+ cells. Purified DC were obtained by immunomagnetic separation plus cell sorting. DC had the morphology of immature myeloid cells, were endocytically active, expressed low levels of co-stimulatory molecules and stimulated a weak allogeneic mixed leucocyte reaction. Analysis of flow cytometry data by a sensitive subtraction method allowed measurement of production of interleukin (IL)-12 and IL-10 by small numbers of gut DC by intracellular staining. Fewer than 5% of unstimulated DC produced either IL-10 or IL-12. IL-10 production was significantly up-regulated following stimulation with Bifidobacteria longum, but not after exposure to lipopolysaccharide (LPS) or Streptococcus faecium. In contrast, colonic DC produced IL-12 in response to both LPS and B.longum. Thus, colonic DC can produce both IL-12 and IL-10 following bacterial stimulation. Cell wall components from different bacteria stimulate distinct responses and may direct immune responses differentially in the gut.
Dietary n-3 polyunsaturated fatty acids suppress splenic CD4+ T cell function in interleukin (IL)-10–/– mice
Authors: Ly L H , Smith R , Chapkin R S , McMurray D N 
Published: January 2005

SummaryOur laboratory has demonstrated that down-regulation of proliferation and cytokine synthesis by CD4+ T cells in mice fed diets rich in n-3 polyunsaturated fatty acids (PUFA) is highly dependent on the involvement of the co-stimulatory molecule, CD28. It has been reported that the inhibitory cytokine interleukin (IL)-10 acts directly on T cells which up-regulate IL-10 receptor (IL-10R) expression following stimulation via CD28 by efficiently blocking proliferation and cytokine production. Thus, it was hypothesized that dietary n-3 PUFA would suppress T cell function through the effects of IL-10. The proliferation of purified splenic CD4+ T cells activated in vitro with anti-CD3 and anti-CD28 (αCD3/CD28) from conventional mice (C57BL/6) fed either a control corn oil (CO)-enriched diet devoid of n-3 PUFA, docosahexaenoic acid (DHA; 22 : 6) or eicosapentaenoic acid (EPA; 20 : 5) for 14 days was suppressed by dietary DHA and EPA. Surprisingly, a similar trend was seen in IL-10 gene knock-out (IL-10–/–) mice fed dietary n-3 PUFA. IL-10R cell surface expression was also significantly down-regulated on CD4+ T cells from both the C57BL/6 and IL-10–/– mice fed dietary n-3 PUFA after 72 h of in vitro stimulation with αCD3/CD28. Enzyme-linked immunosorbent assay (ELISA) measurements revealed that C57BL/6 mice fed DHA had significantly reduced interferon (IFN)-γ and IL-10 levels 48 h post-activation. However, CD4+ T cells from IL-10–/– mice fed dietary n-3 PUFA produced significantly greater levels of IFN-γ than the CO-fed group. Our data suggest that in the absence of IL-10, CD4+ T cells from n-3 PUFA-fed mice may up-regulate IFN-γ. Suppressed CD4+ T cells from n-3 PUFA-fed C57BL/6 mice may use mechanisms other than IL-10 to down-regulate T cell function.
Effects of prolactin and cortisol on natural killer (NK) cell surface expression and function of human natural cytotoxicity receptors (NKp46, NKp44 and NKp30)
Authors: Mavoungou E , Bouyou-Akotet M K , Kremsner P G 
Published: January 2005

SummaryThe surface density of the triggering receptors (e.g. NKp46 and NKp30) responsible for natural killer (NK) cell-mediated cytotoxicity determines the ability of NK cells to kill susceptible target cells. In this study, we show that prolactin up-regulates and cortisol down-regulates the surface expression of NKp46 and NKp30. The prolactin-mediated activation and the cortisol-mediated inhibition of natural cytotoxicity receptor (NCR) surface expression reflects gene regulation at the transcriptional level. NKp46 and NKp30 are the major receptors involved in the NK-mediated killing of K562, a human chronic myelogenous leukaemia cell line. Accordingly, the prolactin dramatically increased the NK-mediated killing of the K562 cell line, whereas cortisol abolished this activity. Our data suggest a mechanism by which prolactin activates the lytic function of NK cells, and cortisol inhibits the NK-mediated attack.
Analysis of the susceptibility of CD57+ T cells to CD3-mediated apoptosis
Authors: Shinomiya N , Koike Y , Koyama H , Takayama E , Habu Y , Fukasawa M , Tanuma S , Seki S 
Published: January 2005

SummaryAfter stimulation with anti-CD3 antibody in vitro, CD57+ T cells showed a greater susceptibility to apoptosis than CD57–αβT cell receptor (TCR)+ T cells (regular αβ T cells). The apoptotic fraction of CD57+ T cells showed an increased production of active caspase-3. An increase in both Fas expression and Fas-ligand (FasL) production was also observed in CD57+ T cells, whereas the expression of survivin was suppressed in CD57+ T cells compared to that of regular αβ T cells. CD57+ T cells display a biased expansion of a few Vβ T cell fractions in individuals, but such Vβ T cells were not specifically susceptible to CD3-mediated apoptosis. The TCR expression level of CD57+ T cells was much lower than that of regular T cells and anti-TCR antibody stimulation induced a smaller apoptotic proportion of CD57+ T cells than did anti-CD3 antibody. Although the CD3ɛ expression levels were similar in both T cell subsets, the CD3ζ level of CD57+ T cells was significantly higher than that of regular T cells. These results suggest that several apoptotic and anti-apoptotic molecules are involved in the CD3-induced apoptosis of CD57+ T cells and raise the possibility that the imbalance in expression of the CD3ɛ and CD3ζ chains may also contribute to the susceptibility of CD57+ T cells to undergo apoptosis.