Na(+)-K(+)-ATPase alpha 1- and beta 1-subunit degradation: evidence for multiple subunit specific rates

Sex differences in renal transporters: assessment and functional consequences

Mammalian kidneys are specialized to maintain fluid and electrolyte homeostasis. The epithelial transport processes along the renal tubule that match output to input have long been the subject of experimental and theoretical study. However, emerging data have identified a new dimension of investigation: sex. Like most tissues, the structure and function of the kidney is regulated by sex hormones and chromosomes. Available data demonstrate sex differences in the abundance of kidney solute and electrolyte transporters, establishing that renal tubular organization and operation are distinctly different in females and males. Newer studies have provided insights into the physiological consequences of these sex differences. Computational simulations predict that sex differences in transporter abundance are likely driven to optimize reproduction, enabling adaptive responses to the nutritional requirements of serial pregnancies and lactation - normal life-cycle changes that challenge the ability of renal transporters to maintain fluid and electrolyte homeostasis. Later in life, females may also undergo menopause, which is associated with changes in disease risk. Although numerous knowledge gaps remain, ongoing studies will provide further insights into the sex-specific mechanisms of sodium, potassium, acid-base and volume physiology throughout the life cycle, which may lead to therapeutic opportunities.

Quercetin regulates skeletal muscle fiber type switching via adiponectin signaling

This study aimed to investigate the role and underlying molecular mechanism of quercetin in regulating skeletal muscle fiber type transition. We found that dietary quercetin supplementation in mice significantly increased oxidative fiber-related gene expression, slow-twitch fiber percentage and succinic dehydrogenase (SDH) activity. By contrast, quercetin decreased lactate dehydrogenase (LDH) activity, fast MyHC protein expression, fast-twitch fiber percentage, and MyHC IIb mRNA expression. Furthermore, quercetin significantly increased serum adiponectin (AdipoQ) concentration, and the expression levels of AdipoQ and AdipoR1. However, inhibition of adiponectin signaling by AdipoR1 siRNA significantly attenuated the effects of quercetin on muscle fiber type-related gene expression, the percentages of slow MyHC-positive and fast MyHC-positive fibers, and metabolic enzyme activity in C2C12 myotubes. Together, our data indicated that quercetin could promote skeletal fiber switching from glycolytic type II to oxidative type I through AdipoQ signaling.

Type 1 Diabetes and Physical Exercise: Moving (forward) as an Adjuvant Therapy

Type 1 diabetes is characterized by an autoimmune β-cell destruction resulting in endogenous insulin deficiency, potentially leading to micro- and macrovascular complications. Besides an exogenous insulin therapy and continuous glucose monitoring, physical exercise is recommended in adults with type 1 diabetes to improve overall health. The close relationship between physical exercise, inflammation, muscle contraction, and macronutrient intake has never been discussed in detail about type 1 diabetes. The aim of this narrative review was to detail the role of physical exercise in improving clinical outcomes, physiological responses to exercise and different nutrition and therapy strategies around exercise. Physical exercise has several positive effects on glucose uptake and systemic inflammation in adults with type 1 diabetes. A new approach via personalized therapy adaptations must be applied to target beneficial effects on complications as well as on body weight management. In combination with pre-defined macronutrient intake around exercise, adults with type 1 diabetes can expect similar physiological responses to physical exercise, as seen in their healthy counterparts. This review highlights interesting findings from recent studies related to exercise and type 1 diabetes. However, there is limited research available accompanied by a proper number of participants in the cohort of type 1 diabetes. Especially for this group of patients, an increased understanding of the impact of physical exercise can improve its effectiveness as an adjuvant therapy to move (forward).

Dose-response relationships between sedentary behaviour and the metabolic syndrome and its components

AIMS/HYPOTHESIS

The aim of this study was to examine the relationship among sedentary behaviour (SB) and the metabolic syndrome and its components by age, moderate-to-vigorous physical activity (MVPA) and sex.

METHODS

A cross-sectional analysis was performed on 2003-2006 National Health and Nutrition Examination Survey data from 5,076 adults aged ≥18 years (mean ± SD = 43.8 ± 19.5). SB was measured using ActiGraph accelerometers worn for 1 week and defined as <100 counts/min. Metabolic syndrome was defined using the Adult Treatment Panel III criteria. Natural cubic spline logistic regression models were used to estimate the odds of meeting criteria for the metabolic syndrome and its components by total daily SB time and breaks in SB. Statistical interactions between SB and age, sex and MVPA were explored.

RESULTS

The prevalence of the metabolic syndrome was 19% and the average daily SB time was 8.1 ± 2.8 h, with 90 ± 25 breaks/day. The relationship between daily SB time and the metabolic syndrome was linear and characterised by an OR of 1.09 (95% CI 1.01, 1.18) for each hour of SB. Total SB was associated with the following components: high triacylglycerol, low HDL-cholesterol and high fasting glucose. All three associations were modified by MVPA level. No relationship between breaks in SB and the metabolic syndrome was found.

CONCLUSIONS/INTERPRETATION

There appears to be no SB threshold at which the risk of the metabolic syndrome is elevated. Therefore, an effort should be made to maintain low levels of total time spent in SB and so lessen the risk of the metabolic syndrome.

Targeting GRPR in urological cancers--from basic research to clinical application

Gastrin releasing peptide (GRP) is a regulatory peptide that acts through its receptor (GRPR) to regulate physiological functions in various organs. GRPR is overexpressed in neoplastic cells of most prostate cancers and some renal cell cancers and in the tumoral vessels of urinary tract cancers. Thus, targeting these tumours with specifically designed GRP analogues has potential clinical application. Potent and specific radioactive, cytotoxic or nonradioactive GRP analogues have been designed and tested in various animal tumour models with the aim of receptor targeting for tumour diagnosis or therapy. All three categories of compound were found suitable for tumour targeting in animal models. The cytotoxic and nonradioactive GRP analogues have not yet shown convincing tumour-reducing effects in human trials; however, the first clinical studies of radioactive GRP analogues--both agonists and antagonists--suggest promising opportunities for both diagnostic tumour imaging and radiotherapy of prostate and other GRPR-expressing cancers.

Old and new peptide receptor targets in cancer: future directions

A precise definition of the tumor tissue targets to be selected for in vivo peptide receptor targeting, namely to know which peptide receptor is expressed in which type of cancer, is an important prerequisite for successful clinical application of this technology. In this short review, I give three selected examples of new and promising peptide receptor targets. In the somatostatin receptor field, based on in vitro receptor autoradiography experiments showing that much more sst(2) binding sites are detected in tumors using a (177)Lu-labeled sst(2) antagonist than a (177)Lu-labeled agonist, it can be proposed that, in addition to neuroendocrine tumors, nonneuroendocrine tumors with lower sst(2) levels such as breast carcinomas, renal cell carcinomas, and non-Hodgkin lymphomas may become potential candidates for sst(2) antagonist targeting. In the gastrin-releasing peptide receptor field, recent in vitro data show that not only tumor cells may overexpress gastrin-releasing peptide receptors but also neoangiogenic tumoral vessels, making tumors expressing high levels of gastrin-releasing peptide receptors in tumor vessels, such as ovarian or urinary tract cancers, attractive new candidates for gastrin-releasing peptide receptor targeting. In the incretin receptor field, it was found in vitro that, apart from glucagon-like peptide 1 receptors overexpressed in benign insulinomas, incretin receptors, especially the glucose-dependent insulinotropic polypeptide receptors, can be overexpressed in medullary thyroid cancers, an unexpected finding making also these tumors potential novel candidates for incretin receptor targeting. Due to the abundance of peptide receptors in various cancers, it may be possible in the future to define for each tumor type a corresponding overexpressed peptide receptor suitable for targeting.

A meal test improves the specificity of chromogranin A as a marker of neuroendocrine neoplasia

Chromogranin A (CgA) is a neuroendocrine tumor (NET) marker. Modest CgA elevation is found in subjects with enterochromaffin-like (ECL) cell hyperplasia due to hypergastrinemia. Somatostatin analogs reduce CgA levels in patients with NET. Meals may affect serum CgA levels. The aims of the study were to investigate meal-induced CgA release and the short-term effect of octreotide on serum CgA levels. Four groups were studied: group A, seven patients with ECL cell hyperplasia secondary to use of proton pump inhibitors (PPIs); group B, six patients with gastric carcinoid type 1/ECL hyperplasia due to chronic atrophic gastritis (CAG); group C, six patients with nongastric NETs; group D, seven controls. The subjects were studied on three separate days with the use of three exposures: a test meal, pentagastrin subcutaneously (not group C), and octreotide intravenously. Serum CgA and gastrin were analyzed. A test meal induced a significant CgA increase in long-term PPI users and in healthy controls. The meal did not affect CgA levels in patients with gastric carcinoid type 1 or patients with NETs. The test meal increased gastrin levels in all groups except in those with CAG. Pentagastrin increased CgA levels in all groups tested except in those with CAG, while octreotide, reduced CgA and gastrin levels in all groups. Serum CgA should be determined in fasting individuals. A test meal may distinguish between increased CgA levels in PPI users from nongastric NET patients. Concomitant gastrin determination may help to discriminate between nongastric NETs and CAG. Intravenous octreotide rapidly reduces serum CgA.

Spontaneous calcium spike activity in embryonic spinal neurons is regulated by developmental expression of the Na+, K+-ATPase beta3 subunit

Different types and patterns of spontaneous electrical activity drive many aspects of neuronal differentiation. Neurons in the developing Xenopus spinal cord exhibit calcium spikes, which regulate gene transcription and neurotransmitter specification. The ionic currents necessary for spike production have been described. However, the mechanisms that generate the onset of this activity and the basis of its regulation remain unclear. Although signaling molecules appear to act on plasma membrane receptors to trigger calcium spike activity, other mechanisms for spontaneous calcium spike regulation may exist as well. Here, we analyze the developmental expression of the Na(+), K(+)-ATPase beta3 subunit in Xenopus tropicalis embryos and show that its levels are downregulated at a time during embryonic development that coincides with the onset of prominent calcium spike activity in spinal neurons. Inhibition of an earlier increase in beta3 expression leads to more depolarized resting membrane potentials and results in later reduction of spike activity. This suppression of beta3 levels also reduces expression of the store-operated calcium channel subunit, Orai1. These findings suggest that the Na(+), K(+)-ATPase plays a role in initiating calcium spike activity and regulating calcium homeostasis.

Ubiquitination participates in the lysosomal degradation of Na,K-ATPase in steady-state conditions

The alveolar epithelial cell (AEC) Na,K-ATPase contributes to vectorial Na(+) transport and plays an important role in keeping the lungs free of edema. We determined, by cell surface labeling with biotin and immunofluorescence, that approximately 30% of total Na,K-ATPase is at the plasma membrane of AEC in steady-state conditions. The half-life of the plasma membrane Na,K-ATPase was about 4 hours, and the incorporation of new Na,K-ATPase to the plasma membrane was Brefeldin A sensitive. Both protein kinase C (PKC) inhibition with bisindolylmaleimide (10 microM) and infection with an adenovirus expressing dominant-negative PKCzeta prevented Na,K-ATPase degradation. In cells expressing the Na,K-ATPase alpha1-subunit lacking the PKC phosphorylation sites, the plasma membrane Na,K-ATPase had a moderate increase in half-life. We also found that the Na,K-ATPase was ubiquitinated in steady-state conditions and that proteasomal inhibitors prevented its degradation. Interestingly, mutation of the four lysines described to be necessary for ubiquitination and endocytosis of the Na,K-ATPase in injurious conditions did not have an effect on its half-life in steady-state conditions. Lysosomal inhibitors prevented Na,K-ATPase degradation, and co-localization of Na,K-ATPase and lysosomes was found after labeling and chasing the plasma membrane Na,K-ATPase for 4 hours. Accordingly, we provide evidence suggesting that phosphorylation and ubiquitination are necessary for the steady-state degradation of the plasma membrane Na,K-ATPase in the lysosomes in alveolar epithelial cells.

beta-Subunit overexpression alters the stoicheometry of assembled Na-K-ATPase subunits in MDCK cells

In eukaryotic cells, the apparent maintenance of 1:1 stoicheometry between the Na-K-ATPase alpha- and beta-subunits led us to question whether this was alterable and thus if some form of regulation was involved. We have examined the consequences of overexpressing Na-K-ATPase beta1-subunits using Madin-Darby canine kidney (MDCK) cells expressing flag-tagged beta1-subunits (beta1flag) or Myc-tagged beta1-subunits (beta1myc) under the control of a tetracycline-dependent promoter. The induction of beta1flag subunit synthesis in MDCK cells, which increases beta1-subunit expression at the plasma membrane by more than twofold, while maintaining stable alpha1 expression levels, revealed that all mature beta1-subunits associate with alpha1-subunits, and no evidence of "free" beta1-subunits was obtained. Consequently, the ratio of assembled beta1- to alpha1-subunits is significantly increased when "extra" beta-subunits are expressed. An increased beta1/alpha1 stoicheometry is also observed in cells treated with tunicamycin, suggesting that the protein-protein interactions involved in these complexes are not dependent on glycosylation. Confocal images of cocultured beta1myc-expressing and beta1flag-expressing MDCK cells show colocalization of beta1myc and beta1flag subunits at the lateral membranes of neighboring cells, suggesting the occurrence of intercellular interactions between the beta-subunits. Immunoprecipitation using MDCK cells constitutively expressing beta1myc and tetracycline-regulated beta1flag subunits confirmed beta-beta-subunit interactions. These results demonstrate that the equimolar ratio of assembled beta1/alpha1-subunits of the Na-K-ATPase in kidney cells is not fixed by the inherent properties of the interacting subunits. It is likely that cellular mechanisms are present that regulate the individual Na-K-ATPase subunit abundance.

Changes in gene expression of gastric mucosa during therapeutic acid inhibition

BACKGROUND

Long-term therapy with potent acid inhibitors is a common treatment for gastro-esophageal reflux disease. Administration of proton pump inhibitors (PPIs) causes profound and continuous hypochlorhydria by inhibition of the proton pump in gastric parietal cells. Long-term hypergastrinaemia increases mucosal thickness and enterochromaffin-like cell density in oxyntic mucosa.

OBJECTIVE

The aim of this study was to see whether this very common clinical intervention induces significant changes in the gastric mucosal gene expression pattern.

METHODS

Seven patients suffering from gastro-esophageal reflux disease were included in this study. Endoscopic biopsies were taken from the corpus mucosa before and toward the end of a 3-month treatment with the PPI esomeprazole.

RESULTS

Microarray analysis identified 186 differentially expressed genes. A high proportion of genes with changed gene expression levels during PPI treatment are involved in proliferation, apoptosis, and stress response.

CONCLUSION

This study identified many genes that were not previously known to be affected by inhibition of gastric acid secretion. Further characterization of the functional roles of genes whose expression is modulated by potent acid inhibition may give new insight into the biological responses to potent acid inhibition, including the mucosal response to the moderately increased gastrin levels encountered in clinical practice.

Gastrin transactivates the chromogranin A gene through MEK-1/ERK- and PKC-dependent phosphorylation of Sp1 and CREB

Our previous work revealed that gastrin regulates chromogranin A (CgA) transcription through enhanced binding of Sp1, CREB and Egr-1 to a proximal gastrin-responsive promoter element (Gas-RE). Here, we provide a detailed characterization of the signalling pathways transmitting the effect of gastrin on the CgA promoter. Gastrin treatment of gastric AGS-B cells potently stimulated MEK-1 as well as MAP kinases ERK-1/-2, JNK and p38 in a time-dependent manner. Interruption of ERK-1/-2/MEK-1 pathways abolished the transactivating effect of gastrin, whereas blockade of JNK or p38 activity was without effect. Functional promoter analysis revealed that the minimal element CgA-85/-64 was sufficient and necessary to confer MEK-1/ERK responsiveness. Analysis of proximal signalling pathways showed that activation of the MEK-1/ERK-1/2 module by gastrin does not require Ras, PI3-kinase or intracellular calcium signals, but depends on activation of kinases of the PKC family. This report demonstrates that a pathway comprising PKCs>Raf-1>MEK-1>ERK-1/-2 mediates the effect of gastrin on the CgA promoter, and strongly suggests that enhanced phosphorylation of Sp1 and CREB is crucial for CgA transactivation through the G protein-coupled CCK-B/gastrin receptor.

Identification of a Gastrin Response Element in the Vesicular Monoamine Transporter Type 2 Promoter and Requirement of 20 S Proteasome Subunits for Transcriptional Activity

Vesicular monoamine transporter type 2 (VMAT2) is crucial for accumulation of monoamine neurotranmitters into neuronal secretory vesicles and histamine into secretory granules of the enterochromaffin-like cell in the acid-secreting gastric mucosa. Gastric VMAT2 expression is regulated by the antral hormone gastrin acting at the CCK(2) receptor. We demonstrate a gastrin response element (-56)ccgccccctc(-47) in the proximal VMAT2 promoter that binds in a gastrin-sensitive manner to nuclear proteins from gastric epithelial cell lines. Mutations within this sequence prevented nuclear protein binding and significantly reduced gastrin-stimulated expression of VMAT2 promoter-reporter constructs in gastric epithelial cells. In a yeast one-hybrid screen of an AR42J cell cDNA library, using the gastrin response element as bait, we identified a beta subunit of the 20 S proteasome, PSMB1, as a potential binding partner. In supershift assays, antibodies to PSMB1 and other proteasome beta subunits disrupted gastrin sensitive nuclear protein binding to the VMAT2 promoter. Moreover, RNA interference of PSMB1 significantly inhibited gastrin-mediated VMAT2 transcription. These data suggest that elements of the 20 S proteasome interact with the VMAT2 promoter to enhance G-protein-coupled receptor-mediated transcription.

Molecular impact of clenbuterol and isometric strength training on rat EDL muscles

Clenbuterol, a beta2-adrenergic-receptor agonist, is known to provoke muscle hypertrophy and a slow-to-fast phenotype change. A more glycolytic phenotype should be paralleled by changes in muscle glycolytic metabolism. Two groups (n=16 for each) of 3-month-old male Wistar rats (UCL: untrained clenbuterol, and ECL: exercised clenbuterol) received a chronic administration of clenbuterol (2 mg/kg body weight/day). Two other groups of animals (U: untrained and E: exercised), were given a 0.9% NaCl solution instead of clenbuterol. E and ECL animals followed an 8-week progressive isometric force strength-training program. Both clenbuterol administration and training resulted in an increase in extensor digitorum longus (EDL) mass despite the fact that this muscle was indirectly mobilised during isometric force strength training. Clenbuterol and training induced a consistent slow-to-fast phenotype change without drastically increasing specific activities of glycolytic enzymes. Except for GAPDH and hexokinase, modifications in glycolytic-enzyme-specific activities were not explained by transcriptional changes. Lactate dehydrogenase activity was not affected by clenbuterol but was strongly augmented by training. In EDL of ECL rats, both treatments presented an opposite effect compensating each other. GLUT1 mRNA expression was augmented in EDL of UCL and ECL animals, whereas monocarboxylate transporter 1 mRNA amounts were decreased in EDL of UCL rats. Citrate synthase activity was reduced by clenbuterol treatment but remained unchanged in EDL of E animals. Creatine kinase activity was enhanced only by clenbuterol alone. These data show that clenbuterol-induced muscle hypertrophy and slow-to-fast phenotype changes are not associated with a glycolytic-enzyme-activity increase. They also suggest that in EDL isometric force strength training can reverse clenbuterol-induced molecular adaptations.

Helicobacter pylori infection stimulates intestinalization of endocrine cells in glandular stomach of Mongolian gerbils

Intestinal metaplasia has been investigated extensively as a possible premalignant condition for stomach cancer but its pathogenesis is still not fully understood. In the present study, we examined the relationship between endocrine and mucous cell marker expression periodically after Helicobacter pylori infection in the Mongolian gerbil model. The numbers of chromogranin A (CgA)-positive, gastrin-positive and gastric inhibitory polypeptide (GIP)-positive cells in H. pylori-infected groups was increased significantly compared with the non-infected case. However, CgA-positive and gastrin-positive cells then decreased from 50 through 100 experimental weeks after H. pylori infection, whereas GIP-positive cells increased. Coexistence of gastrin-positive and GIP-positive cells was detected in the same gastric and intestinal mixed phenotypic glandular-type glands. In conclusion, the endocrine cell phenotype is in line with that of the mucous counterpart in the glands of H. pylori-infected Mongolian gerbil stomach, supporting the concept that development of intestinal metaplasia is due to the abnormal differentiation of a stem cell.

Hybrid assemblies of ATP-sensitive K+ channels determine their muscle-type-dependent biophysical and pharmacological properties

ATP-sensitive K(+) channels (K(ATP)) are an octameric complex of inwardly rectifying K(+) channels (Kir6.1 and Kir6.2) and sulfonylurea receptors (SUR1 and SUR2A/B), which are involved in several diseases. The tissue-selective expression of the subunits leads to different channels; however, the composition and role of the functional channel in native muscle fibers is not known. In this article, the properties of K(ATP) channels of fast-twitch and slow-twitch muscles were compared by combining patch-clamp experiments with measurements of gene expression. We found that the density of K(ATP) currents/area was muscle-type specific, being higher in fast-twitch muscles compared with the slow-twitch muscle. The density of K(ATP) currents/area was correlated with the level of Kir6.2 expression. SUR2A was the most abundant subunit expressed in all muscles, whereas the vascular SUR2B subunit was expressed but at lower levels. A significant expression of the pancreatic SUR1 was also found in fast-twitch muscles. Pharmacological experiments showed that the channel response to the SUR1 agonist diazoxide, SUR2A/B agonist cromakalim, SUR1 antagonist tolbutamide, and the SUR1/SUR2A/B-antagonist glibenclamide matched the SURs expression pattern. Muscle-specific K(ATP) subunit compositions contribute to the physiological performance of different muscle fiber types and determine the pharmacological actions of drugs modulating K(ATP) activity in muscle diseases.

Gastric achlorhydria in H/K-ATPase-deficient (Atp4a(-/-)) mice causes severe hyperplasia, mucocystic metaplasia and upregulation of growth factors

BACKGROUND

Gastric neoplasia is common in humans, yet controversy remains over contributions of chronic achlorhydria, gastrinemia and hyperplasia, to cancer risk. To study this, mice lacking the gastric H/K-ATPase (Atp4a(-/-) mice) were used to determine whether chronic loss of acid secretion, with attendant hypergastrinemia, predisposes to cancer phenotype.

METHODS

Atp4a(-/-) and Atp4a(+/+) mice, paired for age and gender, were examined at 3, 8, 12 and 20 months for histopathology, and for expression of the trefoil factor family (TFF)1-3, Reg IIIbeta, gamma and delta, osteopontin, CD44, chromogranin A, Crp-ductin, and galectin, all of which are important in cell growth.

RESULTS

By 8 months, the glandular stomach of the Atp4a(-/-) mice doubled in weight and thickness, and several modulators of growth were increased. Female Atp4a(-/-) mice were more hyperplastic than Atp4a(-/-) males at 12 and 20 months. By 1 year, severe mucocystic hyperplasia, incomplete intestinal metaplasia, ciliated metaplasia, a shift in mucins from neutral to acidic, and inflammation were widespread. Cells in the mucus pit zone developed a pyloric-type appearance, containing large hyaline-like, periodic acid-Schiff (PAS)-negative/alcian blue-negative inclusions. But critical characteristics of gastric neoplasia, such as nuclear atypia, invasion into the muscularis mucosa, and metastases were absent. In Atp4a(-/-) mice, chromogranin A and histidine decarboxylase, RegIIIgamma and delta, TFF3, osteopontin and CD44 were upregulated while Reg IIIbeta, and TFF1 were reduced.

CONCLUSIONS

Chronic achlorhydria and hypergastrinemia in aged Atp4a(-/-) mice produced progressive hyperplasia, mucocystic and incomplete intestinal metaplasia, and the upregulation of growth factors without histological evidence of neoplasia.

Inhibition of calcineurin increases monocarboxylate transporters 1 and 4 protein and glycolytic enzyme activities in rat soleus muscle

1. The present study was designed to examine the role of calcineurin in muscle metabolic components by the administration of the specific calcineurin inhibitor cyclosporine A (CsA) to rats. 2. Male Wistar rats were divided into either a CsA-treated group (CT) or a vehicle-treated group (VT). Cyclosporine A was administered subcutaneously to rats at a rate of 25 mg/kg bodyweight per day for 10 successive days. Thereafter, changes in muscle enzyme activities and glucose transporter (GLUT)-4 and monocarboxylate transporter (MCT)-1 and MCT-4 proteins in the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles were examined. 3. There was a significant increase in MCT-1 and MCT-4 proteins in the soleus muscle in the CT group, but not in the EDL muscle. The activities of hexokinase, pyruvate kinase and lactate dehydrogenase in the soleus muscle also increased significantly in the CT group, but a similar increase in enzyme activity was not seen in EDL muscle. The activities of citrate synthase or malate dehydrogenase and the GLUT-4 protein content were not altered by CsA treatment in either the soleus or EDL muscles. 4. These results seem to imply that calcineurin negatively regulates the components of glucose/lactate metabolism, except for GLUT-4, especially in slow-twitch muscle.

Subunit-specific coordinate upregulation of sodium pump activity in alveolar epithelial cells by lentivirus-mediated gene transfer

Resolution of alveolar edema depends on active ion transport by sodium pumps located on the basolateral surface of alveolar epithelial cells (AECs), suggesting that upregulation of sodium pump activity may facilitate clearance of edema fluid. We have investigated the use of lentiviral vectors to augment sodium pump activity via gene transfer of sodium pump subunits to AECs. Full-length cDNA for the alpha(1) or beta(1) subunit of rat Na(+),K(+)-ATPase was cloned into the lentiviral vector pRRLsin.hCMV.IRES.EGFP. Rat AECs in primary culture were transduced on day 4 with lentiviral vectors pseudotyped with vesicular stomatitis virus glycoprotein G. Transduction with lentiviral vectors encoding either alpha(1) subunit (Lenti-alpha(1)-EGFP) or beta(1) subunit (Lenti-beta(1)-EGFP) led to dose-dependent increases in mRNA and protein for the corresponding subunit. Transduction with Lenti-beta(1)-EGFP was accompanied by coordinate upregulation of endogenous alpha(1) expression, whereas endogenous beta(1) expression was unchanged after transduction with Lenti-alpha(1)-EGFP. Consistent with these findings, transduction with Lenti-beta(1)-EGFP, but not Lenti-alpha(1)-EGFP, led to augmentation of sodium pump activity as a result of increases in Na(+),K(+)-ATPase holoenzyme. Sodium pump alpha(2) subunit and sodium channel protein did not change after Lenti-beta(1)-EGFP transduction. These results demonstrate that overall sodium pump activity can be efficiently upregulated in AECs specifically via gene transfer of the sodium pump beta(1) subunit and support the feasibility of lentivirus-mediated gene transfer to augment alveolar fluid clearance.

Expression, regulation and function of Na,K-ATPase in the lens

Na,K-ATPase is responsible for maintaining the correct concentrations of sodium and potassium in lens cells. Na,K-ATPase activity is different in the two cell types that make up the lens, epithelial cells and fibers; specific activity in the epithelium is higher than in fibers. In some parts of the fiber mass Na,K-ATPase activity is barely detectable. There is a large body of evidence that suggests Na,K-ATPase-mediated ion transport by the epithelium contributes significantly to the regulation of ionic composition in the entire lens. In some species different Na,K-ATPase isoforms are present in epithelium and fibers but in general, fibers and epithelium express a similar amount of Na,K-ATPase protein. Turnover of Na,K-ATPase by protein synthesis may contribute to preservation of high Na,K-ATPase activity in the epithelium. In ageing lens fibers, oxidation, and glycation may decrease Na,K-ATPase activity. Na,K-ATPase activity in lens fibers and epithelium also may be subject to regulation as the result of protein tyrosine phosphorylation. Moreover, activation of G protein-coupled receptors by agonists such as endothelin-1 elicits changes of Na,K-ATPase activity. The asymmetrical distribution of Na,K-ATPase activity in the epithelium and fibers may contribute to ionic currents that flow in and around the lens. Studies on human cataract and experimental cataract in animals reveal changes of Na,K-ATPase activity but no clear pattern is evident. However, there is a convincing link between abnormal elevation of lens sodium and the opacification of the lens cortex that occurs in age-related human cataract.

Dexamethasone responsive element in the rat Na, K-ATPase beta1 gene coding region

The Na, K-ATPase plays an essential role in active alveolar epithelial fluid resorption. In fetal and adult alveolar epithelial cells, glucocorticoids (GC) increase Na, K-ATPase activity, mRNA levels, and transcription rate of the beta(1) subunit. In this study, we describe a glucocorticoid responsive element (GRE) in the coding region of the rat Na, K-ATPase beta(1) gene in a rat lung epithelial cell line. Transient transfection experiments with the beta(1) subunit coding region with or without the 5' and 3' untranslated regions demonstrated responsiveness to dexamethasone induction and also identified a GRE at +434 in exon IV. The +434 GRE conferred dexamethasone responsiveness in a heterologous thymidine kinase promoter irrespective of its orientation to the beta(1) promoter. Transcriptional upregulation by dexamethasone was abolished in +434 mutants. Electrophoretic mobility shift assays (EMSA) demonstrated specific binding of nuclear proteins to the +434 GRE and the presence of the GC receptor. This specific binding was inhibited by a GRE previously described in the rat Na, K-ATPase beta(1) gene at -631. In conclusion, we identified a GRE at +434 in the exon IV of the rat Na, K-ATPase beta(1) gene.

Exercise training increases the activity of pyruvate dehydrogenase complex in skeletal muscle of diabetic rats

The effects of diabetes and exercise training on the activity of pyruvate dehydrogenase (PDH) complex in skeletal muscle were examined in rats. Male Sprague-Dawley rats were divided into four groups as follows: non-diabetic sedentary, non-diabetic trained, diabetic sedentary, and diabetic trained groups. Diabetic rats were prepared by a bolus injection of intravenous streptozotocin (50 mg/kg body weight). Exercise training was performed by having rats run on a treadmill at a speed of 25 m/min for 45 min/day, 6 days/wk for 4 wks. Exercise training decreased serum concentrations of glucose and non-esterified fatty acid in diabetic rats. GLUT4 content in skeletal muscle in sedentary rats was significantly decreased by diabetes; however, exercise training significantly increased the GLUT4 content in diabetic rats. The total and actual activities and the proportion of actual activity of the PDH complex were decreased in diabetic sedentary rats. Exercise training did not affect the total activity of the PDH complex in non-diabetic rats, whereas it increased the total activity in diabetic rats to the same level as that in non-diabetic rats. In diabetic rats, exercise training tended to increase the proportion of actual activity of the PDH complex from 2.7 +/- 0.4% to 4.7 +/- 0.8%, although the proportion of actual activity in non-diabetic rats was decreased by exercise training. The present study suggests that exercise training may improve glucose metabolism in the skeletal muscle of streptozotocin-induced diabetic rats probably through the mechanisms of increasing both GLUT4 content and the activity of the PDH complex.

GLUT4 expression at the plasma membrane is related to fibre volume in human skeletal muscle fibres

In this study we examined the relationship between GLUT4 expression at the plasma membrane and muscle fibre size in fibre-typed human muscle fibres by immunocytochemistry and morphometry in order to gain further insight into the regulation of GLUT4 expression. At the site of the plasma membrane, GLUT4 was more abundantly expressed in slow as compared to fast fibres at the same fibre diameter (p < 0.01) and the GLUT4 expression increased with increasing fibre radius independently of fibre type (p < 0.01). The GLUT4 density at the surface of slow fibres of both diabetic and obese was reduced compared to control subjects at the same diameter (p < 0.001). Fast fibres in obese and type 2 diabetic subjects expressed a fibre-volume-dependent GLUT4 expression (p < 0.001), while this did not reach significance in slow fibres (obese p = 0.18 and diabetic p = 0.06). Our results show that increasing fibre volume is associated with increasing GLUT4 expression in both slow and fast fibres. Based on the possible dependency of GLUT4 expression on volume, we hypothesize that the reduced GLUT4 expression in obesity and type 2 diabetes may partly be compensated for by physical activity.

Skeletal muscle regulates extracellular potassium

Maintaining extracellular fluid (ECF) K(+) concentration ([K(+)]) within a narrow range is accomplished by the concerted responses of the kidney, which matches K(+) excretion to K(+) intake, and skeletal muscle, the main intracellular fluid (ICF) store of K(+), which can rapidly buffer ECF [K(+)]. In both systems, homologous P-type ATPase isoforms are key effectors of this homeostasis. During dietary K(+) deprivation, these P-type ATPases are regulated in opposite directions: increased abundance of the H,K-ATPase "colonic" isoform in the renal collecting duct drives active K(+) conservation while decreased abundance of the plasma membrane Na,K-ATPase alpha(2)-isoform leads to the specific shift of K(+) from muscle ICF to ECF. The skeletal muscle response is isoform and muscle specific: alpha(2) and beta(2), not alpha(1) and beta(1), levels are depressed, and fast glycolytic muscles lose >90% alpha(2), whereas slow oxidative muscles lose ~50%; however, both muscle types have the same fall in cellular [K(+)]. To understand the physiological impact, we developed the "K(+) clamp" to assess insulin-stimulated cellular K(+) uptake in vivo in the conscious rat by measuring the exogenous K(+) infusion rate needed to maintain constant plasma [K(+)] during insulin infusion. Using the K(+) clamp, we established that K(+) deprivation leads to near-complete insulin resistance of cellular K(+) uptake and that this insulin resistance can occur before any decrease in plasma [K(+)] or muscle Na(+) pump expression. These studies establish the advantage of combining molecular analyses of P-type ATPase expression with in vivo analyses of cellular K(+) uptake and excretion to determine mechanisms in models of disrupted K(+) homeostasis.

Chronic leptin administration decreases fatty acid uptake and fatty acid transporters in rat skeletal muscle

Chronic leptin administration reduces triacylglycerol content in skeletal muscle. We hypothesized that chronic leptin treatment, within physiologic limits, would reduce the fatty acid uptake capacity of red and white skeletal muscle due to a reduction in transport protein expression (fatty acid translocase (FAT/CD36) and plasma membrane-associated fatty acid-binding protein (FABPpm)) at the plasma membrane. Female Sprague-Dawley rats were infused for 2 weeks with leptin (0.5 mg/kg/day) using subcutaneously implanted miniosmotic pumps. Control and pair-fed animals received saline-filled implants. Leptin levels were significantly elevated (approximately 4-fold; p < 0.001) in treated animals, whereas pair-fed treated animals had reduced serum leptin levels (approximately -2-fold; p < 0.01) relative to controls. Palmitate transport rates into giant sarcolemmal vesicles were reduced following leptin treatment in both red (-45%) and white (-84%) skeletal muscle compared with control and pair-fed animals (p < 0.05). Leptin treatment reduced FAT mRNA (red, -70%, p < 0.001; white, -48%, p < 0.01) and FAT/CD36 protein expression (red, -32%; p < 0.05) in whole muscle homogenates, whereas FABPpm mRNA and protein expression were unaltered. However, in leptin-treated animals plasma membrane fractions of both FAT/CD36 and FABPpm protein expression were significantly reduced in red (-28 and -34%, respectively) and white (-44 and -56%, respectively) muscles (p < 0.05). Across all experimental treatments and muscles, palmitate uptake by giant sarcolemmal vesicles was highly correlated with the plasma membrane FAT/CD36 protein (r = 0.88, p < 0.01) and plasma membrane FABPpm protein (r = 0.94, p < 0.01). These studies provide the first evidence that protein-mediated long chain fatty acid transport is subject to long term regulation by leptin.

Insulin action and long-term electrically induced training in individuals with spinal cord injuries

PURPOSE

Individuals with spinal cord injuries (SCI) have an increased prevalence of insulin resistance and type 2 diabetes mellitus. In able-bodied individuals, training with large muscle groups increases insulin sensitivity and may prevent type 2 diabetes mellitus. However, individuals with SCI cannot voluntarily recruit major muscle groups, but by functional electrical stimulation (FES) they can now perform ergometer bicycle training.

METHODS

Ten subjects with SCI (35 +/- 2 yr (mean +/- SE), 73 +/- 5 kg, level of lesion C6--Th4, time since injury: 12 +/- 2 yr) performed 1 yr of FES cycling (30 min x d(-1), 3 d x wk(-1) (intensive training)). Seven subjects continued 6 months with reduced training (1 d x wk(-1) (reduced training)). A sequential, hyperinsulinemic (50 mU x min(-1) x m(-2) (step 1) and 480 mU x min(-1) x m(-2) (step 2)), euglycemic clamp, an oral glucose tolerance test (OGTT), and determination of GLUT 4 transporter protein in muscle biopsies were performed before and after training.

RESULTS

Insulin-stimulated glucose uptake rates increased after intensive training (from 4.9 +/- 0.5 mg x min(-1) x kg(-1) to 6.2 +/- 0.6 mg x min(-1) x kg(-1) (P < 0.008) (step 1) and from 9.0 +/- 0.8 mg x min(-1) x kg(-1) to 10.6 +/- 0.8 mg x min(-1) x kg(-1) (P = 0.103) (step 2)). With the reduction in training, insulin sensitivity decreased to a similar level as before training (P > 0.05). GLUT 4 increased by 105% after intense training and decreased again with the training reduction. The subjects had impaired glucose tolerance before and after training, and neither glucose tolerance nor insulin responses to OGTT were significantly altered by training.

CONCLUSIONS

Electrically induced bicycle training, performed three times per week increases insulin sensitivity and GLUT 4 content in skeletal muscle in subjects with SCI. A reduction in training to once per week is not sufficient to maintain these effects. FES training may have a role in the prevention of the insulin resistance syndrome in persons with SCI.

A novel role of neuregulin in skeletal muscle. Neuregulin stimulates glucose uptake, glucose transporter translocation, and transporter expression in muscle cells

Neuregulins regulate the expression of acetylcholine receptor genes and induce development of the neuromuscular junction in muscle. In studying whether neuregulins regulate glucose uptake in muscle, we analyzed the effect of a recombinant neuregulin, (r)heregulin-beta1-(177-244) (HRG), on L6E9 muscle cells, which express the neuregulin receptors ErbB2 and ErbB3. L6E9 responded acutely to HRG by a time- and concentration-dependent stimulation of 2-deoxyglucose uptake. HRG-induced stimulation of glucose transport was additive to the effect of insulin. The acute stimulation of the glucose transport induced by HRG was a consequence of the translocation of GLUT4, GLUT1, and GLUT3 glucose carriers to the cell surface. The effect of HRG on glucose transport was dependent on phosphatidylinositol 3-kinase activity. HRG also stimulated glucose transport in the incubated soleus muscle and was additive to the effect of insulin. Chronic exposure of L6E9 cells to HRG potentiated myogenic differentiation, and under these conditions, glucose transport was also stimulated. The activation of glucose transport after chronic HRG exposure was due to enhanced cell content of GLUT1 and GLUT3 and to increased abundance of these carriers at the plasma membrane. However, under these conditions, GLUT4 expression was markedly down-regulated. Muscle denervation is associated with GLUT1 induction and GLUT4 repression. In this connection, muscle denervation caused a marked increase in the content of ErbB2 and ErbB3 receptors, which occurred in the absence of alterations in neuregulin mRNA levels. This fact suggests that neuregulins regulate glucose transporter expression in denervated muscle. We conclude that neuregulins regulate glucose uptake in L6E9 muscle cells by mechanisms involving the recruitment of glucose transporters to the cell surface and modulation of their expression. Neuregulins may also participate in the adaptations in glucose transport that take place in the muscle fiber after denervation.

Transcriptional activation of the rat vesicular monoamine transporter 2 promoter in gastric epithelial cells: regulation by gastrin

Vesicular monoamine transporter 2 is important for the accumulation of monoamine neurotransmitters into synaptic vesicles and histamine transport into secretory vesicles of the enterochromaffin-like cell of the gastric corpus. In this study we have investigated the mechanisms regulating the transcriptional activation of the rat vesicular monoamine transporter 2 (VMAT2) promoter in gastric epithelial cells. Maintenance of basal levels of transcription was dependent on the presence of SP1, cAMP-response element (CRE), and overlapping AP2/SP1 consensus sequences within the region of promoter from -86 to +1 base pairs (bp). Gastrin stimulation increased transcriptional activity, and responsiveness was shown to be dependent on the CRE (-33 to -26 bp) and AP2/SP1 (-61 to -48 bp) consensus sites but independent of the SP1 site at -86 to -81 bp. Gastrin-induced transcription was dependent on the cooperative interaction of an uncharacterized nuclear factor of approximately 23.3 kDa that bound to the putative AP2/SP1 site, CRE-binding protein (CREB), and CREB-binding protein/p300. Gastrin stimulation resulted in the increased binding of phosphorylated CREB to the promoter, but it did not result in the increased binding of the AP2/SP1-binding protein. The gastrin responsiveness of the promoter was shown to be dependent on both the protein kinase C and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-signaling pathways, which may converge on the AP2/SP1-binding protein.

Synthesis of gill Na(+)-K(+)-ATPase in Atlantic salmon smolts: differences in alpha-mRNA and alpha-protein levels

Several parameters were analyzed to determine the mechanisms responsible for the enhancement of the gill Na(+)-K(+)-ATPase activity of Atlantic salmon smolts. A major alpha-subunit transcript of 3.7 kb was revealed by Northern blot in both parr and smolt gills when hybridized with two distinct cDNA probes. The alpha-mRNA abundance demonstrated an increase to maximal levels in smolts at an early stage of the parr-smolt transformation. This was followed by a gradual rise in alpha-protein levels, revealed by Western blots with specific antibodies and by an increase in gill Na(+)-K(+)-ATPase hydrolytic activity, both only reaching maximum levels a month later, at the peak of the transformation process. Parr fish experienced a decrease in alpha-mRNA abundance and had basal levels of alpha-protein and enzyme activity. Measurement of the binding of [(3)H]ouabain to Na(+)-K(+)-ATPase was characterized in smolts and parr gill membranes showing more than a twofold elevation in smolts and was of high affinity in both groups (dissociation constant = 20-23 nM). Modulation of the enzyme due to increased salinity was also observed in seawater-transferred smolts, as demonstrated by an increase in alpha-mRNA levels after 24 h with a rise in Na(+)-K(+)-ATPase activity occurring only after 11 days. No qualitative change in alpha-expression was revealed at either the mRNA or protein level. Immunological identification of the alpha-protein was performed with polyclonal antibodies directed against the rat alpha-specific isoforms, revealing that parr, freshwater, and seawater smolts have an alpha(3)-like isoform. This study shows that the increase in Na(+)-K(+)-ATPase activity in smolt gills depends first on an increase in the alpha-mRNA expression and is followed by a slower rise in alpha-protein abundance that eventually leads to a higher synthesis of Na(+)-K(+) pumps.

Activation of human histidine decarboxylase gene promoter activity by gastrin is mediated by two distinct nuclear factors

The human histidine decarboxylase gene is regulated by gastrin through a cis-acting element known as the gastrin response element (GAS-RE) that was initially localized to a site (+2 to +24) downstream of the transcriptional start site. Electrophoretic mobility shift assays using sequentially deleted DNA probes and nuclear extracts from AGS-B gastric cancer cells showed that the GAS-RE is actually composed of two overlapping binding sites (GAS-RE1, +1 to +19; and GAS-RE2, +11 to +27) that bind distinct nuclear factors. Reporter gene assays demonstrated that each element alone could confer gastrin responsiveness, but the presence of both elements was required for complete gastrin response. Stimulation of AGS-B cells with gastrin for 10-20 min resulted in a >2-fold increase in factor binding. The binding was inhibited by pretreatment of AGS-B cells with cycloheximide and the MEK1 inhibitor PD98059, indicating a requirement for protein synthesis and also indicating that activation occurs through the MEK/mitogen-activated protein kinase pathway. UV cross-linking and Southwestern blot analysis showed that GAS-RE1 bound a 52-kDa protein, whereas GAS-RE2 bound a 35-kDa protein. Hence, activation of histidine decarboxylase gene promoter activity by gastrin is most likely mediated by two separate nuclear factors.

Temporal responses of oxidative vs. glycolytic skeletal muscles to K+ deprivation: Na+ pumps and cell cations

When K+ output exceeds input, skeletal muscle releases intracellular fluid K+ to buffer the fall in extracellular fluid (ECF) K+. To investigate the mechanisms and muscle specificity of the K+ shift, rats were fed K+-deficient chow for 2-10 days, and two muscles at phenotypic extremes were studied: slow-twitch oxidative soleus and fast-twitch glycolytic white gastrocnemius (WG). After 2 days of low-K+ chow, plasma K+ concentration ([K+]) fell from 4.6 to 3.7 mM, and Na+-K+-ATPase alpha2 (not alpha1) protein levels in both muscles, measured by immunoblotting, decreased 36%. Cell [K+] decreased from 116 to 106 mM in soleus and insignificantly in WG, indicating that alpha2 can decrease before cell [K+]. After 5 days, there were further decreases in alpha2 (70%) and beta2 (22%) in WG, not in soleus, whereas cell [K+] decreased and cell [Na+] increased by 10 mM in both muscles. By 10 days, plasma [K+] fell to 2.9 mM, with further decreases in WG alpha2 (94%) and beta2 (70%); cell [K+] fell 19 mM in soleus and 24 mM in WG compared with the control, and cell [Na+] increased 9 mM in soleus and 15 mM in WG; total homogenate Na+-K+-ATPase activity decreased 19% in WG and insignificantly in soleus. Levels of alpha2, beta1, and beta2 mRNA were unchanged over 10 days. The ratios of alpha2 to alpha1 protein levels in both control muscles were found to be nearly 1 by using the relative changes in alpha-isoforms vs. beta1- (soleus) or beta2-isoforms (WG). We conclude that the patterns of regulation of Na+ pump isoforms in oxidative and glycolytic muscles during K+ deprivation mediated by posttranscriptional regulation of alpha2beta1 and alpha2beta2 are distinct and that decreases in alpha2-isoform pools can occur early enough in both muscles to account for the shift of K+ to the ECF.

Sp1 and CREB mediate gastrin-dependent regulation of chromogranin A promoter activity in gastric carcinoma cells

Chromogranin A (CgA) is a multifunctional acidic protein that in the stomach is expressed predominantly in enterochromaffin-like cells (ECL cells) where it is regulated by gastrin. In order to investigate the transcriptional response of the mouse CgA (mCgA) promoter to gastrin stimulation, we studied a 4.8-kilobase mCgA promoter-luciferase reporter gene construct in transiently transfected AGS-B cells. 5'-Deletion analysis and scanning mutagenesis of mCgA 5'-flanking DNA showed that a Sp1/Egr-1 site spanning -88 to -77 base pairs (bp) and a cyclic AMP-responsive element (CRE) at -71 to -64 bp are essential for gastrin-dependent mCgA transactivation. Gastrin stimulation increased cellular Sp1 protein levels and Sp1-binding to the mCgA -88 to -77 bp element, as well as binding of CREB to its consensus motif at -71 to -64 bp. Gastrin also stimulated CREB Ser-133 phosphorylation, and abundance of cellular CREB protein levels. Overexpression of either Sp1 or phosphorylated CREB transactivated the mCgA promoter dose dependently, while coexpression of both transcription factors resulted in an additive mCgA promoter response. mCgA -92 to -64 bp, comprising the Sp1/Egr-1 site and the CRE motif, conferred gastrin responsiveness to a heterologous thymidine kinase promoter system, and therefore functions as a "true" enhancer element. This report demonstrates that Sp1 and CREB mediate CCK-B/gastrin receptor-dependent gene regulation, and that the effect of gastrin on the CgA gene is brought about by cooperative action of both transcription factors.

Augmentation of lung liquid clearance via adenovirus-mediated transfer of a Na,K-ATPase beta1 subunit gene

Previous studies have suggested that alveolar Na,K-ATPases play an important role in active Na+ transport and lung edema clearance. We reasoned that overexpression of Na,K-ATPase subunit genes could increase Na,K-ATPase function in lung epithelial cells and edema clearance in rat lungs. To test this hypothesis we produced replication deficient human type 5 adenoviruses containing cDNAs for the rat alpha1 and beta1 Na,K-ATPase subunits (adMRCMValpha1 and adMRCMVbeta1, respectively). As compared to controls, adMRCMVbeta1 increased beta1 subunit expression and Na,K-ATPase function by 2. 5-fold in alveolar type 2 epithelial cells and rat airway epithelial cell monolayers. No change in Na,K-ATPase function was noted after infection with adMRCMValpha1. Rat lungs infected with adMRCMVbeta1, but not adMRCMValpha1, had increased beta1 protein levels and lung liquid clearance 7 d after tracheal instillation. Alveolar epithelial permeability to Na+ and mannitol was mildly increased in animals infected with adMRCMVbeta1 and a similar Escherichia coli lacZ-expressing virus. Our data shows, for the first time, that transfer of the beta1 Na,K-ATPase subunit gene augments Na,K-ATPase function in epithelial cells and liquid clearance in rat lungs. Conceivably, overexpression of Na,K-ATPases could be used as a strategy to augment lung liquid clearance in patients with pulmonary edema.

Overexpression of the Na+,K+-ATPase alpha1 subunit increases Na+,K+-ATPase function in A549 cells

We hypothesized that viral mediated transfer of Na+,K+-ATPase subunit genes to alveolar epithelial cells to overexpress Na+, K+-ATPase could increase Na+,K+-ATPase function. We produced replication-deficient human type 5 adenoviruses that contained cytomegalovirus (CMV)-driven cDNAs for the rat alpha1 and beta1 subunits of Na+,K+-ATPase (AdMRCMValpha1 and AdMRCMVbeta1, respectively). These viruses were used to transduce human adenocarcinoma cells (A549) in culture. Na+,K+-ATPase function was increased by 2.5-fold in the AdMRCMValpha1-infected cells. Sham and AdMRCMVbeta1-infected cells, and cells infected by a CMV-driven beta-galactosidase-expressing adenovirus, had no increases in Na+, K+-ATPase activity. A549 cells infected with multiplicities of infection of 10-200 of AdMRCMValpha1 demonstrated expression of a rat alpha1 mRNA and increased alpha1 protein; no change in beta1 message or protein was noted. Ouabain sensitivity was measured in A549 cells following infection with AdMRCMValpha1. In contrast to controls, AdMRCMValpha1-infected cells demonstrated two IC50s. The first was similar to the IC50s of the controls; the second IC50 was 2 logs greater than the first, consistent with the presence of both the rat and human alpha1 isozymes. These results demonstrate for the first time that adenoviruses can be used to augment Na+,K+-ATPase function.

Modulation of lung liquid clearance by isoproterenol in rat lungs

beta-Adrenergic agonists have been reported to increase lung liquid clearance by stimulating active Na+ transport across the alveolar epithelium. We studied mechanisms by which beta-adrenergic isoproterenol (Iso) increases lung liquid clearance in isolated perfused fluid-filled rat lungs. Iso perfused through the pulmonary circulation at concentrations of 10(-4) to 10(-8) M increased lung liquid clearance compared with that of control lungs (P < 0.01). The increase in lung liquid clearance was inhibited by the beta-antagonist propranolol (10(-5) M), the Na(+)-channel blocker amiloride (10(-4) M), and the antagonist of Na-K-ATPase, ouabain (5 x 10(-4) M). Colchicine, which inhibits cell microtubular transport of ion-transporting proteins to the plasma membrane, blocked the stimulatory effects of Iso on active Na+ transport, whereas the isomer lumicolchicine, which does not affect cell microtubular transport, did not inhibit Na+ transport. In parallel with these changes, the Na-K-ATPase alpha 1-subunit protein abundance and activity increased in alveolar type II cells stimulated by 10(-6) M Iso. Colchicine blocked the stimulatory effect of Iso and the recruitment of Na-K-ATPase alpha 1-protein to the basolateral membrane of alveolar type II cells. Accordingly, Iso increased active Na+ transport and lung liquid clearance by stimulation of beta-adrenergic receptors and probably by upregulation of apical Na+ channels and basolateral Na-K-ATPase mechanisms. Recruitment from intracellular pools and microtubular transport of Na+ pumps to the plasma membrane participate in beta-adrenergic stimulation of lung liquid clearance in rat lungs.

Dexamethasone upregulates the Na-K-ATPase in rat alveolar epithelial cells

Previous studies in kidney, heart, and liver cells have demonstrated that dexamethasone regulates the expression of Na-K-ATPase. In the lungs, Na-K-ATPase has been reported in alveolar epithelial type II (ATII) cells and is thought to participate in active Na+ transport and lung edema clearance. The aim of this study was to determine whether Na-K-ATPase would be regulated by dexamethasone in cultured rat ATII cells. Regulation of the Na-K-ATPase by dexamethasone could lead to a greater understanding of its role in active Na+ transport and lung edema clearance. Rat ATII cells were isolated, plated for 24 h, and exposed to 10(-7) and 10(-8) M dexamethasone. These cells were harvested at 0, 3, 6, 12, and 24 h after dexamethasone exposure for determination of steady-state Na-K-ATPase mRNA transcript levels, protein expression, and function. The steady-state Na-K-ATPase beta1-mRNA transcript levels increased in ATII cells 6, 12, and 24 h after dexamethasone exposure (P < 0.05). However, the steady-state alpha1-mRNA transcript levels were unchanged. The protein expression for the alpha1- and beta1-subunits increased in ATII cells exposed to dexamethasone compared with controls in association with a temporal increase in Na-K-ATPase function after dexamethasone exposure. These results suggest that dexamethasone regulates Na-K-ATPase in ATII cells possibly by transcriptional, translational, and posttranslational mechanisms.

Neuroendocrine cells in the prostate of the rat, guinea pig, cat, and dog

BACKGROUND

The neuroendocrine (NE) cells in the human prostate gland probably have a local regulatory role in both prostatic growth and differentiation as well as in the exocrine secretory process. Moreover, NE cells may be involved in the pathogenesis of both prostatic cancer and hyperplasia. To enhance the knowledge of the physiological and pathophysiological role of NE cells in the prostate gland, we wanted to establish an experimental animal model.

METHODS

All lobes of the prostatic complex of rats with different serum levels of testosterone, as well as the prostate of the guinea pig, cat, and dog, were studied. Prostatic tissue fixed in different fixatives was studied with regard to NE cells by using cytochemical and immunohistochemical staining techniques, as well as Northern blotting and reverse transcriptase polymerase chain reaction (RT-PCR) for detection of rat chromogranin A (CgA) mRNA.

RESULTS

The present study indicates the absence of NE cells in the rat prostatic complex. No expression of CgA RNA was detectable either by Northern blotting or by RT-PCR. Only a few argyrophil cells in the prostatic complex of guinea pig were detected in tissue fixed in Bouin's solution.

CONCLUSIONS

Rat, guinea pig, cat, and dog are not suitable animals in physiological studies of NE cells in the prostate gland.

Distribution of prohormone convertase-6 expression in the gastrointestinal tract and effects of a fasting-refeeding regimen and a high-fat diet on ileal prohormone convertase-6 expression

Proforms of gastrointestinal peptide hormones and neuropeptides are processed, in part, by prohormone convertases (PCs) to mature, biologically active peptides. The purpose of this study was to characterize the mRNA levels of PC-6 isoforms, PC-6A and PC-6B, in the gastrointestinal tract and pancreas of the rat, and to investigate the effects of a fasting and refeeding regimen, and a high-fat diet on ileal PC-6A expression. PC-6A mRNA is expressed throughout the entire gastrointestinal tract with the highest levels in the small intestine. Multiple-sized transcripts are present. PC-6B mRNA is expressed in the antrum and fundus of the stomach, in the small intestine, and colon. Ileal PC-6A mRNA expression increases significantly with fasting and then declines with refeeding toward control levels. Increased dietary fat increases PC-6A mRNA levels in the ileum. Since PC-6 is found throughout the entire gastrointestinal tract, it is likely that PC-6 participates in the processing of proforms of gastrointestinal peptides. The two isoforms of PC-6 have different patterns of distribution in the gastrointestinal tract and pancreas, suggesting that they process proforms of different gut peptides.

Evaluation of biologic gastrin activity of compound CI-988 in the isolated, vascularly perfused rat stomach

BACKGROUND

The peptoid CI-988 has previously been shown to have high affinity for the cholecystokinin (CCK)-B/gastrin receptor and has been reported to be a powerful CCK antagonist in many systems, although it has agonist activity on histidine decarboxylase in the rat.

METHODS

In the present study the effect of CI-988 on acid secretion and histamine release in the totally isolated, vascularly perfused rat stomach was assessed.

RESULTS

CI-988 was found to be a gastrin agonist with regard to the stimulation of both histamine release and acid secretion.

CONCLUSION

Thus, in this stomach model CI-988 behaved as a CCKB/gastrin agonist. The present study underlines the importance of testing the biologic activity of ligands in models with sufficient sensitivity.

Human vascular endothelium heterogeneity. A comparative study of cerebral and peripheral cultured vascular endothelial cells

BACKGROUND AND PURPOSE

Hormones, neurotransmitters, and autacoids play a key role in the regulation of vascular tone as a result of their interaction with the endothelium. The aim of this study was to compare selected properties of three human endothelial cell lines isolated from cerebral pial arteries (PEC) and two peripheral vessels, the superficial temporal (SEC) and omental (OEC) arteries.

METHODS

Intracellular free calcium concentration ([Ca2+]i) and receptor protein expression were measured in characterized primary cultures of human endothelial cells.

RESULTS

All cell lines labeled positively for factor VIII/von Willebrand factor. Growth rate and constitutive release of endothelin-1, expressed as a function of protein, were both significantly lower in cerebral cells (PEC) than in endothelial cells derived from peripheral vessels. Basal [Ca2+]i measured with the fluorescent calcium indicator fura 2-AM (2 mumol/L) did not differ in either of the three cell lines. Although PEC responded to endothelin-1 (0.1 mumol/L) and vasoactive intestinal peptide (1 mumol/L) by a twofold to threefold increase in [Ca2+]i, OEC were unresponsive to these peptides. Moreover, the calcium response to alpha-thrombin (10 nmol/L) was greater in cerebral (PEC) than in peripheral (SEC, OEC) endothelial cells, while bradykinin (100 nmol/L) increased [Ca2+]i to a similar level in all three cell types.

CONCLUSIONS

This study demonstrates that endothelial cells from different sites of the vasculature exhibit different growth rates and vary in their response to agonists.

Depletion of enterochromaffin-like cell histamine increases histidine decarboxylase and chromogranin A mRNA levels in rat stomach by a gastrin-independent mechanism

BACKGROUND

Gastrin activates histidine decarboxylase (HDC) and increases HDC and chromogranin A (CGA) mRNA levels in histamine-producing enterochromaffin-like (ECL) cells in the rat stomach. We have studied how histamine depletion by subcutaneous infusion of the HDC inhibitor alpha-fluoromethyl-histidine (alpha-FMH) affects how ECL cells respond to hypergastrinemia in terms of HDC and CGA mRNA levels.

METHODS

In one experiment rats received alpha-FMH for 24 h. In another experiment rats received alpha-FMH, omeprazole (perorally), or a combination of the two drugs for 10 days. In a third experiment antrectomized rats were treated with alpha-FMH for 48 h. The circulating gastrin level, oxyntic mucosal histamine concentration, HDC activity, and HDC and CGA mRNA levels were determined.

RESULTS

alpha-FMH for 24 h increased the HDC and CGA mRNA levels without increasing the serum gastrin concentration. alpha-FMH for 10 days increased the serum gastrin concentration twofold. alpha-FMH + omeprazole resulted in the same serum gastrin concentration as after omeprazole alone (eightfold increase). HDC mRNA levels were higher after alpha-FMH + omeprazole than after omeprazole alone. alpha-FMH alone induced an HDC mRNA level that was similar in magnitude to that observed after omeprazole, although the serum gastrin concentration after alpha-FMH was much lower. In antrectomized rats alpha-FMH increased the HDC and CGA mRNA levels without increasing the serum gastrin concentration.

CONCLUSION

ECL-cell histamine depletion will increase mRNA levels for HDC and CGA by a gastrin-independent mechanism, possibly involving abolished histamine autofeedback inhibition.