Pericytes. Morphofunction, interactions and pathology in a quiescent and activated mesenchymal cell niche

We review the morphofunctional characteristics of pericytes and report our observations. After a brief historical background, we consider the following aspects of pericytes: A) Origin in embryonic vasculogenesis (mesenchymal stem cells, neurocrest and other possible sources) and in embryonic and postnatal life angiogenesis (pre-existing pericytes, fibroblast/ myofibroblasts and circulating progenitor cells). B) Location in pericytic microvasculature and in the other blood vessels (including transitional cell forms and absence in lymphatic vessels), incidence (differences depending on species, topographical location, and type and stage of vessels) and distribution (specific polarities) in blood vessels. C) Morphology (cell body, and longitudinal and circumferential cytoplasmic processes), structure (nucleus, cytoplasmic organelles and distribution of microtubules, intermediate filaments and microfilaments) and surface (caveolae system). D) Basement membrane disposition, formation, components and functions. E) Contacts with endothelial cells (ECs) (peg and socket arrangements, adherent junctions and gap junctions) and with basal membrane (adhesion plaques). F) Molecular expression (pericyte marker identification). G) Functions, such as vessel stabilization, regulation of vascular tone and maintenance of local and tissue homeostasis (contractile capacity and vessel permeability regulation), matrix protein synthesis, macrophage-like properties, immunological defense, intervention in coagulation, participation in mechanisms that regulate the quiescent and angiogenic stages of blood vessels (including the behaviour of pericytes during sprouting angiogenesis and intussuceptive vascular growth, as well as pericyte interactions with endothelium and other cells, and with extracellular matrix) and plasticity, as progenitor cells with great mesenchymal potential, originating other pericytes, fibroblast/myofibroblasts, preadipocytes, chondroblasts, osteoblasts, odontoblasts, vascular smooth muscle and myointimal cells. This mesenchymal capacity is seen in a broad section on the perivascular mesenchymal cell niche hypothesis and in the concept of pericyte and EC "marriage and divorce". H) Peculiar pericyte types, such as hepatic stellate cells (Ito cells), bone marrow reticular cells and mesangial cells. I) Involvement in pathological processes, such as repair through granulation tissue, pericyte-derived tumors, tumor angiogenesis and tumoral cell metastasis, diabetic microangiopathy, fibrosis, atherosclerosis and calcific vasculopathy, lymphedema distichiasis, chronic venous insufficiency, pulmonary hypertension, Alzheimer disease and multiple sclerosis. J) Clinical and therapeutic implications (de-stabilization of vessels or formation of a stable vasculature).

[Study on the role of the tubule in renal vasoconstriction induced by cyclosporine]

INTRODUCTION

Cyclosporine (CyA) has proved to induce cell apoptosis on cultured proximal tubule cells. However, there is no much data about the in vivo functional consequences of this injury or the long time observed CyA-induced renal vasoconstriction.

MATERIAL AND METHODS

In a swine model of subacute CyA nephrotoxicity (10 mg/ Kg. dx 15 days), we performed a right nephrectomy, followed by left renal artery, vein and ureter catheterisati8n. After inducing water diuresis, three clearance periods of 15 minutes were performed before and after a furosemide 1 mg/kg infusion. Plasma and urine electrolytes, blood gas, acid excretion, plasma renin activity and aldosterone concentration, GFR, RPF, RBF, intra-renal vascular resistances, glomerular filtration pressure, distal Cl- delivery, water clearance and TTKG were measured or estimated on 7 control and 7 treated animals. Right kidney was processed for NaKATPase activity and immunostaining.

RESULTS

Treated animals presented detaching proximal cells, luminal blebbing and loss of tight junctions. Cortical but not medullar sodium pump was internalised and partially inactive. Treated animals showed much lower fractional excretions of Na+, with significantly higher distal fractional reabsorption of Cl. Distal shift in fluid load resulted in a significant rise in renal O2 consumption, and modifications in the global renal estequiometry of Na+ transport/O2 uptake. Several consequences followed this situation: preglomerular resistances increased 3 times with only minor changes in postglomerular resistances and renal blood and plasma flow were significantly reduced. Furosemide partially reversed these effects. A slight increase in fractional filtration prevented GFR differences to become statistically significant.

CONCLUSION

subacute CyA treatment even al doses not modifying GFR, may cause proximal tubule Na+ transport impairment, resulting in increased rates of distal delivery and absorption of fluid load. Renal uptake of O2 may be increased and tubule glomerular feedback should be expected to be activated. Absence of changes of GFR with furosemide is an early sign of CyA renal damage.

[The search for new autoantigens in Sjögren's syndrome]

OBJECTIVE

To identify new autoantigens related to Sjögren's syndrome and to determine their prevalence in patients and healthy individuals.

MATERIAL AND METHODS

Serological sampling was performed in a patient with Sjögren's syndrome through the use of a human brain expression genotec (SEREX technique) to determine expression of known autoantigens and previously undescribed proteins. The presence of a previously unknown protein was found. Several proteins were obtained and two were selected to be studied (a human protein called Tau and an unknown protein described by our group and named hlscA). Both Tau and hIscA cDNA were transformed into an expression plasmid to obtain their recombinant proteins.

RESULTS

Using a Western-blot technique we investigated the presence of anti-Tau and anti-hlscA autoantibodies in the sera of 19 patients with Sjögren's syndrome and in the sera of 20 controls. No statistically significant differences were found in the expression of anti-Tau antibodies between patients with Sjögren's syndrome and controls but values of anti-hlscA autoantibodies were significantly lower in patients with Sjögren's syndrome.

CONCLUSION

We identified Tau and hIscA proteins as new autoantigens in Sjögren's syndrome. Anti-hlscA antibody values were significantly lower in patients with Sjögren's syndrome than in healthy controls. Although no statistically significant differences in values of anti-Tau antibodies were found between Sjögren's syndrome patients and controls, this is the first time antibodies against this protein have been detected in Sjögren's syndrome.

Regeneration influences expression of the Na+, K+-atpase subunit isoforms in the rat peripheral nervous system

Neural injury triggers changes in the expression of a large number of gene families. Particularly interesting are those encoding proteins involved in the generation, propagation or restoration of electric potentials. The expression of the Na+, K+-ATPase subunit isoforms (alpha, beta and gamma) was studied in dorsal root ganglion (DRG) and sciatic nerve of the rat in normal conditions, after axotomy and during regeneration. In normal DRG, alpha1 and alpha2 are expressed in the plasma membrane of all cell types, while there is no detectable signal for alpha3 in most DRG cells. After axotomy, alpha1 and alpha2 expression decreases evenly in all cells, while there is a remarkable onset in alpha3 expression, with a peak about day 3, which gradually disappears throughout regeneration (day 7). beta1 Is restricted to the nuclear envelope and plasma membrane of neurons and satellite cells. Immediately after injury, beta1 shows a homogeneous distribution in the soma of neurons. No beta2 expression was found. Beta3 Specific immunofluorescence appears in all neurons, although it is brightest in the smallest, diminishing progressively after injury until day 3 and, thereafter, increasing in intensity, until it reaches normal levels. FXYD7 is expressed weakly in a few DRG neurons (less than 2%) and Schwann cells. It increases intensely in satellite cells immediately after axotomy, and in all cell types at day 3. Transient switching of members of the Na+, K+-ATPase isoform family elicited by axotomy suggests variations in the sodium pump isozymes with different affinities for Na+, K+ and ATP from those in intact nerve. This adaptation may be important for regeneration.

Human articular chondrocytes, synoviocytes and synovial microvessels express aquaporin water channels; upregulation of AQP1 in rheumatoid arthritis

Recent studies have shown that aquaporin water channels are expressed in human Meckel's cartilage. The aim of the present investigation was to determine if human articular chondrocytes and synoviocytes express aquaporin 1 (AQP1) water channels and to establish if there are any alterations in AQP1 expression in osteoarticular disorders such as osteoarthritis (OA) and rheumatoid arthritis (RA). Immunohistochemistry was employed semi-quantitatively to compare the expression of AQP1 in human chondrocytes derived from normal, OA and RA joints. PCR, cloning and sequencing confirmed the presence of AQP1 transcripts in chondrocytes. Normal human tissue microarrays including samples of kidney, choroid plexus and pancreas were used as positive controls for AQP1 expression. In most tissues AQP1 was expressed along endothelial barriers. In the kidney AQP1 was present in the glomerular capillary endothelium, proximal tubule and descending thin limbs. AQP1 was also localized to pancreatic ducts and acini and the apical membrane domain of the choroid plexus. Immunohistochemistry showed that AQP1 is expressed in synovial micro-vessels, synoviocytes and predominantly in chondrocytes located in the deep zone of articular cartilage. Image analysis of normal, OA and RA cartilage suggested that AQP1 may be upregulated in RA. This is the first report of AQP1 mRNA and protein expression in articular chondrocytes and synoviocytes. These findings suggest a potential role for AQP1 and possibly other members of the AQP gene family in the movement of extracellular matrix and metabolic water across the membranes of chondrocytes and synoviocytes for the purposes of chondrocyte volume regulation and synovial homeostasis.

Expression and cellular localization of Na,K-ATPase isoforms in the rat ventral prostate

OBJECTIVE

To determine the expression and plasma membrane domain location of isoforms of Na,K-ATPase in the rat ventral prostate.

MATERIALS AND METHODS

Ventral prostate glands from adult male rats were dissected, cryosectioned (7 micro m) and attached to poly-l-lysine coated glass slides. The sections were then fixed in methanol and subjected to indirect immunofluorescence and immunoperoxidase procedures using a panel of well-characterized monoclonal and polyclonal antibodies raised against known Na,K-ATPase subunit isoforms. Immunofluorescence micrographs were digitally captured and analysed by image analysis software.

RESULTS

There was expression of Na,K-ATPase alpha1, beta1, beta2 and beta3 subunit isoforms in the lateral and basolateral plasma membrane domains of prostatic epithelial cells. The alpha1 isoform was abundant but there was no evidence of alpha2, alpha3 or gamma isoform expression in epithelial cells. The alpha3 isoform was not detected, but there was a relatively low level of alpha2 isoform expression in the smooth muscle and stroma.

CONCLUSION

Rat prostate Na,K-ATPase consists of alpha1/beta1, alpha1/beta2 and alpha1/beta3 isoenzymes. These isoform proteins were located in the lateral and basolateral plasma membrane domains of ventral prostatic epithelial cells. The distribution and subcellular localization of Na,K-ATPase is different in rodent and human prostate. Basolateral Na,K-ATPase probably contributes to the establishment of transepithelial ionic gradients that are a prerequisite for the uptake of metabolites by secondary active transport mechanisms and active citrate secretion.

Glucose transport and metabolism in chondrocytes: a key to understanding chondrogenesis, skeletal development and cartilage degradation in osteoarthritis

Despite the recognition that degenerative cartilage disorders like osteoarthritis (OA) and osteochondritis dissecans (OCD) may have nutritional abnormalities at the root of their pathogenesis, balanced dietary supplementation programs have played a secondary role in their management. This review emphasizes the importance and role of nutritional factors such as glucose and glucose-derived sugars (i.e. glucosamine sulfate and vitamin C) in the development, maintenance, repair, and remodeling of cartilage. Chondrocytes, the cells of cartilage, consume glucose as a primary substrate for ATP production in glycolysis and utilize glucosamine sulfate and other sulfated sugars as structural components for extracellular matrix synthesis and are dependent on hexose uptake and delivery to metabolic and biosynthetic pools. Data from several laboratories suggests that chondrocytes express multiple isoforms of the GLUT/SLC2A family of glucose/polyol transporters. These facilitative glucose transporter proteins are expressed in a tissue and cell-specific manner, exhibit distinct kinetic properties, and are developmentally regulated. They may also be regulated by endocrine factors like insulin and insulin-like growth factor I (IGF-I) and cytokines such as interleukin 1 beta (IL-1 beta) and tumour necrosis factor alpha (TNF-alpha). Recent studies suggest that degeneration of cartilage may be triggered by metabolic disorders of glucose balance and that OA occurs coincident with metabolic disease, endocrine dysfunction and diabetes mellitus. Based on these metabolic, endocrine and developmental considerations we present a novel hypothesis regarding the role of glucose transport and metabolism in cartilage physiology and pathophysiology and speculate that supplementation with sugar-derived vitamins and nutraceuticals may benefit patients with degenerative joint disorders.

Integrins and stretch activated ion channels; putative components of functional cell surface mechanoreceptors in articular chondrocytes

Perception of mechanical signals and the biological responses to such stimuli are fundamental properties of load bearing articular cartilage in diarthrodial joints. Chondrocytes utilize mechanical signals to synthesize an extracellular matrix capable of withstanding high loads and shear stresses. Recent studies have shown that chondrocytes undergo changes in shape and volume in a coordinated manner with load induced deformation of the matrix. These matrix changes, together with alterations in hydrostatic pressure, ionic and osmotic composition, interstitial fluid and streaming potentials are, in turn, perceived by chondrocytes. Chondrocyte responses to these stimuli are specific and well coordinated to bring about changes in gene expression, protein synthesis, matrix composition and ultimately biomechanical competence. In this hypothesis paper we propose a chondrocyte mechanoreceptor model incorporating key extracellular matrix macromolecules, integrins, mechanosensitive ion channels, the cytoskeleton and subcellular signal transduction pathways that maintain the chondrocyte phenotype, prevent chondrocyte apoptosis and regulate chondrocyte-specific gene expression.

Isoforms of Na+, K+-ATPase in human prostate; specificity of expression and apical membrane polarization

The cellular distribution of Na+, K+-ATPase subunit isoforms was mapped in the secretory epithelium of the human prostate gland by immunostaining with antibodies to the alpha and beta subunit isoforms of the enzyme. Immunolabeling of the alpha1, beta1 and beta2 isoforms was observed in the apical and lateral plasma membrane domains of prostatic epithelial cells in contrast to human kidney where the alpha1 and beta1 isoforms of Na+, K+-ATPase were localized in the basolateral membrane of both proximal and distal convoluted tubules. Using immunohistochemistry and PCR we found no evidence of Na+, K+-ATPase alpha2 and alpha3 isoform expression suggesting that prostatic Na+, K+-ATPase consists of alpha1/beta1 and alpha1/beta2 isozymes. Our immunohistochemical findings are consistent with previously proposed models placing prostatic Na+, K+-ATPase in the apical plasma membrane domain. Abundant expression of Na+, K+-ATPase in epithelial cells lining tubulo-alveoli in the human prostate gland confirms previous conclusions drawn from biochemical, pharmacological and physiological data and provides further evidence for the critical role of this enzyme in prostatic cell physiology and ion homeostasis. Na+, K+-ATPase most likely maintains an inwardly directed Na+ gradient essential for nutrient uptake and active citrate secretion by prostatic epithelial cells. Na+, K+-ATPase may also regulate lumenal Na+ and K+, major counter-ions for citrate.

Oligodendrocytes in brain and optic nerve express the beta3 subunit isoform of Na,K-ATPase

The Na,K-ATPase, which catalyzes the active transport of Na(+) and K(+), has two principal subunits (alpha and beta) that have several genetically distinct isoforms. Most of these isoforms are expressed in the nervous system, but certain ones are preferentially expressed in glia and others in neurons. Of the beta isoforms, beta1 predominates in neurons and beta2 in astrocytes, although there are some exceptions. Here we demonstrate that beta3 is expressed in rat and mouse white matter oligodendrocytes. Immunofluorescence microscopy identified beta3 in oligodendrocytes of rat brain white matter in typical linear arrays of cell bodies between fascicles of axons. The intensity of stain peaked at 20 postnatal days. beta3 was identified in cortical oligodendrocytes grown in culture, where it was expressed in processes and colocalized with antibody to galactocerebroside. In the mouse and rat optic nerve, beta3 stain was seen in oligodendrocytes, where it colocalized with carbonic anhydrase II. For comparison, optic nerve was stained for the beta1 and beta2 subunits, showing distinct patterns of labelling of axons (beta1) and astrocytes (beta2). The C6 glioma cell line was also found to express the beta3 isoform preferentially. Since beta3 was not found at detectable levels in astrocytes, this suggests that C6 is closer to oligodendrocytes than astrocytes in the glial cell lineage.

Na+, K+-ATPase isozyme diversity; comparative biochemistry and physiological implications of novel functional interactions

Na+, K+-ATPase is ubiquitously expressed in the plasma membrane of all animal cells where it serves as the principal regulator of intracellular ion homeostasis. Na+, K+-ATPase is responsible for generating and maintaining transmembrane ionic gradients that are of vital importance for cellular function and subservient activities such as volume regulation, pH maintenance, and generation of action potentials and secondary active transport. The diversity of Na+, K+-ATPase subunit isoforms and their complex spatial and temporal patterns of cellular expression suggest that Na+, K+-ATPase isozymes perform specialized physiological functions. Recent studies have shown that the alpha subunit isoforms possess considerably different kinetic properties and modes of regulation and the beta subunit isoforms modulate the activity, expression and plasma membrane targeting of Na+, K+-ATPase isozymes. This review focuses on recent developments in Na+, K+-ATPase research, and in particular reports of expression of isoforms in various tissues and experiments aimed at elucidating the intrinsic structural features of isoforms important for Na+, K+-ATPase function.

Sodium transport systems in human chondrocytes. I. Morphological and functional expression of the Na+,K(+)-ATPase alpha and beta subunit isoforms in healthy and arthritic chondrocytes

The chondrocyte is the cell responsible for the maintenance of the articular cartilage matrix. The negative charges of proteoglycans of the matrix draw cations, principally Na+, into the matrix to balance the negative charge distribution. The Na+,K(+)-ATPase is the plasma membrane enzyme that maintains the intracellular Na+ and K+ concentrations. The enzyme is composed of an alpha and a beta subunit, so far, 4 alpha and 3 beta isoforms have been identified in mammals. Chondrocytes are sensitive to their ionic and osmotic environment and are capable of adaptive responses to ionic environmental perturbations particularly changes to extracellular [Na+]. In this article we show that human fetal and adult chondrocytes express three alpha (alpha 1, alpha 2 and the neural form of alpha 3) and the three beta isoforms (beta 1, beta 2 and beta 3) of the Na+,K(+)-ATPase. The presence of multiple Na+,K(+)-ATPase isoforms in the plasma membrane of chondrocytes suggests a variety of kinetic properties that reflects a cartilage specific and very fine specialization in order to maintain the Na+/K+ gradients. Changes in the ionic and osmotic environment of chondrocytes occur in osteoarthritis and rheumatoid arthritis as result of tissue hydration and proteoglycan loss leading to a fall in tissue Na+ and K+ content. Although the expression levels and cellular distribution of the proteins tested do not vary, we detect changes in p-nitrophenylphosphatase activity "in situ" between control and pathological samples. This change in the sodium pump enzymatic activity suggests that the chondrocyte responds to these cationic environmental changes with a variation of the active isozyme types present in the plasma membrane.

Sodium transport systems in human chondrocytes. II. Expression of ENaC, Na+/K+/2Cl- cotransporter and Na+/H+ exchangers in healthy and arthritic chondrocytes

In this article, the second of two, we continue our studies of sodium-dependent transport systems in human cartilage from healthy individuals and with osteoarthritis (OA) and rheumatoid arthritis (RA). We demonstrate the presence of the epithelial sodium channel (ENaC), previously undescribed in chondrocytes. This system is composed of three subunits, alpha, beta and gamma. We have shown that the human chondrocytes express at least the alpha and the beta subunit of ENaC. The expression of these subunits is altered in arthritic chondrocytes. In RA samples the quantity of alpha and beta is significantly higher than in control samples. On the other hand, ENaC alpha and beta subunits are absent in the chondrocytes of OA cartilage. Human chondrocytes also possess three isoforms of the Na+/H+ exchanger (NHE), NHE1, NHE2 and NHE3. The NHE system is composed of a single protein and is believed to participate in intracellular pH regulation. Furthermore, our studies indicate that at least one isoform of the electroneutral Na+/K+/2Cl- cotransporter (NKCC) is present in human chondrocytes. There are no obvious variations in the relative expression of NHE isoforms or NKCC between healthy and arthritic cartilage. Our data suggests that chondrocytes from arthritic cartilage may adapt to changes in their environmental sodium concentration through variations in ENaC protein levels. ENaC is also likely to serve as a major sodium entry mechanism, a process that, along with cytoskeletal proteins, may be part of mechanotransduction in cartilage.

Ion transport in chondrocytes: membrane transporters involved in intracellular ion homeostasis and the regulation of cell volume, free [Ca2+] and pH

Chondrocytes exist in an unusual and variable ionic and osmotic environment in the extracellular matrix of cartilage and are responsible for maintaining the delicate equilibrium between extracellular matrix synthesis and degradation. The mechanical performance of cartilage relies on the biochemical properties of the matrix. Alterations to the ionic and osmotic extracellular environment of chondrocytes have been shown to influence the volume, intracellular pH and ionic content of the cells, which in turn modify the synthesis and degradation of extracellular matrix macromolecules. Physiological ion homeostasis is fundamental to the routine functioning of cartilage and the factors that control the integrity of this highly evolved and specialized tissue. Ion transport in cartilage is relatively unexplored and the biochemical properties and molecular identity of membrane transport mechanisms employed by chondrocytes in the control of intracellular ion concentrations and pH is not fully defined and this review focuses on these processes. Chondrocytes have been shown to express voltage and stretch activated ion channels, passive exchangers and ATP dependent ion pumps. In addition, recent studies of transport systems in chondrocytes have demonstrated the presence of isozyme diversity that includes Na+/H+ exchange (NHE1, NHE3), Na+, K(+)-ATPase (several isoforms) and others each of which possess considerably different kinetic properties and modes of regulation. This multitude of isozyme diversity indicates the highly specialized handling of ions and protons in order to accomplish a fine regulation of their transmembrane fluxes. The complexities of these transport systems and their patterns of isoform expression underscore the subtlety of ion homeostasis and pH regulation in normal cartilage. Perturbations in these mechanisms may affect the physiological turnover of cartilage and thus increase the susceptibility to degenerative joint disease.

Structure and expression of the human Na,K-ATPase beta 2-subunit gene

We cloned and characterized the human Na,K-ATPase beta 2-subunit gene. The gene encompasses over 8 kb at chromosome 17 in the human genome and is composed of seven exons. Primer extension analysis identified a major transcription initiation site 529 bases upstream of the translation start site. The 5'-flanking region of the gene harbors a potential TATA sequence, located 94 bases upstream of the transcription initiation site and a number of potential promoter and regulatory elements, among them a Sp1 site, at position -120. A functional Sp1 site has also been found in the rat Na,K-ATPase beta 2-subunit gene (Kawakami, K., Watanabe, Y., Araki, M., Nagano, K., 1993). Sp1 binds to the adhesion molecule on glia regulatory element that functions as a positive transcription regulatory element in astrocytes. (J. Neurosci. Res. 35, 138-146). Putative AATAAA and TG sequences were found at positions 7018 and 7068, respectively. These signals delimit the origin of the the poly(A) tail and mark the end of the sequence that completes the 3'-UT downstream sequence of the human cDNA. An Alu repetitive sequence is located between positions 5961 and 6274. The gene is expressed as a single mRNA species, of 3.36 kb, which is present in cerebrum, cerebellum, kidney and heart, being more abundant in neural tissues. Structural analyses of this and other of the P-type ATPase beta subunit genes reveal that they evolved from a common ancestor.

Expression of the beta-isoforms of Na,K-ATPase in the renal cortex of rats

The aim of the present study was to assess the presence of beta1- and beta2-isoforms of the beta-subunit of Na,K-ATPase in the rat renal cortex. This has been accomplished by immunohistochemistry and Western blotting using isoform-specific antisera. Western blot of brain extract, used as positive control, revealed the bands corresponding to beta1- and beta2-glycosylated peptides, with a molecular weight (MW) of approximately 50-60 that, after exhaustive treatment with N-endoglycosidase-F, migrated to the MW corresponding to the core peptides (approximately 35). In the renal cortex, Western blot revealed the bands corresponding to beta1. After deglycosylation of the samples, the bands hybridizing with the anti-beta1-antibodies moved to the MW corresponding to a partially deglycosylated form and the core peptide. Bands with a MW of approximately 50-60 hybridized with anti-beta2, although digestion with endoglycosidase failed to move the band towards a lower MW. Immunohistochemistry revealed the presence of beta1- but not beta2-isoform. Northern blot for total mRNA showed strong signals for beta1 in renal cortex, the mRNA for the beta2-isoform being undetectable. In conclusion, only mRNA and glycopeptide of the beta1-isoform seem to be present in renal cortex of adult control rats.

Identification of Na(+)-K(+)-ATPase beta-subunit in alveolar epithelial cells

The Na(+)-K(+)-ATPase is a heterodimeric plasma membrane protein that consists of a catalytic alpha-subunit and a smaller glycosylated beta-subunit that has not been fully characterized in alveolar epithelial cells (AEC) to date. In this study, we identified the Na(+)-K(+)-ATPase beta-subunit protein in rat AEC and lung membranes using immunochemical techniques. Rat AEC grown in primary culture and rat lung, brain, and kidney membranes were solubilized in either 2% sodium dodecyl sulfate (SDS) sample buffer for SDS-polyacrylamide gel electrophoresis or in 1% Nonidet P-40 lysis buffer for immunoprecipitation studies. Na(+)-K(+)-ATPase beta-subunit was not detected in either AEC or lung membranes on Western blots when probed with a panel of antibodies (Ab) against beta-subunit isoforms, whereas brain and kidney beta-subunit were recognized as broad approximately 50-kDa bands. AEC, lung, and kidney membranes were immunoprecipitated with anti-beta Ab IEC 1/48, a monoclonal Ab that recognizes beta-subunit protein only in its undenatured state. The beta-subunit was detected in the immunoprecipitate (IP) from kidney membranes by several different anti-beta-subunit Ab. The beta-subunit was faintly detectable from AEC and lung IP as a broad approximately 50-kDa band when blotted with the polyclonal anti-beta 1-subunit Ab SpET but could not be detected by blotting with other anti-beta Ab. Treatment of the IP from kidney, lung, and AEC with N-glycosidase F for 2 h at 37 degrees C resulted in immunodetection of identical approximately 35 kDa bands when probed with all anti-beta 1 Ab on Western blots. From these results, we conclude that rat lung and AEC possess immunoreactive beta-subunit protein that is only readily detectable after deglycosylation. Because anti-beta Ab fail to detect the Na(+)-K(+)-ATPase beta-subunit in rat lung or AEC by standard Western blotting techniques under the conditions of these experiments, our results suggest that lung beta-subunit may be glycosylated differently from kidney and other tissues. These differences appear to be due to organ- or cell-specific posttranslational processing of the beta 1-subunit and may result in altered regulation of sodium pumps in lung compared with other epithelia.

Insulin-induced translocation of Na+-K+-ATPase subunits to the plasma membrane is muscle fiber type specific

We have previously shown that an acute insulin treatment induces redistribution of the alpha 2- and beta 1- isoforms of the Na+-K+-ATPase from intracellular membranes to plasma membranes detected on subcellular fractionation of mixed muscles and immunoblotting with isoform-specific antibodies (H. S. Hundal et al. J. Biol. Chem. 267: 5040-5043, 1992). In the present study we give both biochemical and morphological evidence that this insulin effect is operative in muscles composed mostly of oxidative (red) fibers but not in muscles composed mostly of glycolytic (white) fibers. The redistribution of the Na+-K+-ATPase alpha 2- and beta 1-isoforms after insulin injection was detected in membranes isolated from and muscles (soleus, red gastrocnemius, red rectus femoris, and red vastus lateralis) but not in membranes from white muscles (white gastrocnemius, tensor fasciae latae, white rectus femoris, and white vastus lateralis). After insulin injection, the potassium-dependent 3-O-methylfluorescein phosphatase activity of the enzyme was higher by 22% in the plasma membrane-enriched fraction and lower by 15% in the internal membrane fraction isolated from red but not from white muscles. Quantitative immunoelectron microscopy of ultrathin muscle cryosections showed that in vivo insulin stimulation augmented the density of Na+-K+-ATPase alpha 2- and beta 1- isoforms at the plasma membrane of soleus muscle by 80 and 124%, respectively, with no change in white gastrocnemius muscle. The effect of insulin to increase the content of Na+-K+-ATPase alpha 2- and beta 1-subunits in isolated plasma membranes was still observed when glycemia was prevented from dropping by using hyperinsulinemic-euglycemic clamps. We conclude that the insulin-induced redistribution of the alpha 2- and beta 1-isoforms of the Na+-K+-ATPase from an intracellular pool to the plasma membrane in restricted to oxidative fiber-type skeletal muscles. This may be related to the selective expression of beta 1-subunits in these fibers and implies that the beta 2-subunit, typical of glycolytic muscles, does not sustain translocation of alpha 2 beta 2-complexes.

Expression of the beta 1 and beta 2(AMOG) subunits of the Na,K-ATPase in neural tissues: cellular and developmental distribution patterns

We have used isoform-specific antisera against the Na,K-ATPase beta 1 (SpETb1) and beta 2(AMOG) (SpETb2) subunit isoforms in order to establish their specific cellular and subcellular localization in several developmental stages of the rat central nervous system. Immunocytochemical preparations revealed beta 1 Isoform protein in most neural cells, being predominantly located in the soma of neurons and astrocytes, with no appreciable developmental variations. In the newborn rat, beta 2(AMOG) immunoreactivity was present in cellular processes of astroglia and in the somas of neurons and decreasing in intensity with maturation until adulthood, where no beta 2 isoform was detected in neurons. The differential location of these isoforms, both developmentally and at the cellular level suggest a complex regulation of their genes expression and mechanisms of subcellular distribution, as well as functional differences.

Expression of the beta-subunit isoforms of the Na,K-ATPase in rat embryo tissues, inner ear and choroid plexus

We report evidence of the apical localization of the two Na,K-ATPase beta-subunit isoforms in cells of the inner ear and of the choroid plexus of the rat. To this end, we generated isoform-specific antisera against the human Na,K-ATPase beta 1 and beta 2 subunits. These polyclonal rabbit antisera were raised against truncated beta-isoform proteins that were made in E coli with pET expression vectors. Deglycosylation of the native antigen with N-endoglycosidase F shows four bands in the beta 1 isoform and five bands in the beta 2 isoform immunoblots. In E15 rat embryos, the beta 1 isoform was detected in brain, heart and kidney and the beta 2 isoform only in brain. While beta-subunit mRNA expression (Watts AG, Sanchez-Watts G, Emanuel JR, Levenson R (1991) Proc Natl Acad Sci USA 88, 7425-7429), immunoblotting and enzymatic activity have been determined (Zlokovic BV< mackic JB, Wang L, McComb JG, McDonough A (1993) J Biol Chem 268, 8019-8025), very little is known about the specific localization of each beta-isoform in the epithelia of choroid plexus and inner ear. Immunocytochemical preparations of 15-day-old whole rat embryos and adult rat brain showed an enhanced staining for the beta 1 and beta 2 isoforms in the apical membrane of the ampullary crests of the inner ear's semicircular ducts and in the cuboidal cells of the choroid plexus.

Lewy bodies in tyrosine hydroxylase-synthesizing neurons of the human cerebral cortex

A population of neurons situated in the human cerebral neocortex contains mRNA coding for tyrosine hydroxylase, the key enzyme for catecholamine biosynthesis. Phosphorylated neurofilament-containing cytoplasmic inclusions occur in these neurons in diffuse Lewy body disease, indicating a tendency for selective involvement that is shared with subcortical catecholamine-containing neurons. These findings are relevant to the pathophysiology of several neurologic and psychiatric illnesses in which the monoamine-containing neurons of the neocortex may participate.

4-nitrophenyl phosphatase activity of the red blood cell membrane in essential hypertension

In this paper we report the levels of the 4-nitrophenyl phosphate hydrolysing activity of the red blood cell membrane in 46 hypertensive patients as compared to 41 normal controls and eight secondary hypertensives. This activity has at least two components; one of them is dependent on the presence of magnesium and potassium ions, and more sensitive to sodium, ATP, heat and -SH blockers than the cation-independent activity. This component appears increased in membranes from essential hypertension patients, correlating to the clinical seriousness of the condition, while remaining at control level in the secondary hypertension patients. The cation-independent component of this activity does not differ significantly in any of the groups studied.