Biomedical subjects

N Hernando

Publications and source records attributed to N Hernando.

At least 37 records · Page 2Linked to original sources

PubMed1999

Posttranscriptional regulation of the proximal tubule NaPi-II transporter in response to PTH and dietary P(i).

The rate of proximal tubular reabsorption of phosphate (P(i)) is a major determinant of P(i) homeostasis. Deviations of the extracellular concentration of P(i) are corrected by many factors that control the activity of Na-P(i) cotransport across the apical membrane. In this review, we describe the regulation of proximal tubule P(i) reabsorption via one particular Na-P(i) cotransporter (the type IIa cotransporter) by parathyroid hormone (PTH) and dietary phosphate intake. Available data indicate that both factors determine the net amount of type IIa protein residing in the apical membrane. The resulting change in transport capacity is a function of both the rate of cotransporter insertion and internalization. The latter process is most likely regulated by PTH and dietary P(i) and is considered irreversible since internalized type IIa Na-P(i) cotransporters are subsequently routed to the lysosomes for degradation.

Absorption↗

PubMed1999

[Rh (D) alloimmunization and pregnancy. Analysis of the causes after prophylaxis introduction].

PURPOSE: Prenatal and postnatal prophylaxis of the Rh (D) haemolytic disease of the newborn have clearly reduced the number of cases but still there are alloimmunizations. PATIENTS AND METHODS: All cases detected in our Hospital in the last 24 years have been reviewed and possible causes analyzed. RESULTS: From a total of 10,332 deliveries in Rh (D) negative women we have detected 114 anti-D in 86 women. In 74 women anti-D was the only antibody and in 12 there were more antibodies. Data were managed in 3-year periods and we see a progressive decrease in the incidence of alloimmunization with a minimum of 0.03 per 1000 pregnancies in the period 89-91 and a posterior progression to an incidence of 0.12 in the last 3-year period 95-97. The causes were: pregnancies before 1970 in 31, incorrect prophylaxis in 12, despite a correct prophylaxis in 6, previous pregnancies without complete information about the prophylaxis in 13, previous transfusion in 6, previous pregnancies or transfusion in 8 and indetermined in 10. CONCLUSION: It is desirable to reduce at minimum the number of Rh (D) alloimmunizations by strictly following the prophylaxis protocols.

Erythroblastosis, Fetal↗

PubMed1998

The voltage dependence of a cloned mammalian renal type II Na+/Pi cotransporter (NaPi-2).

The voltage dependence of the rat renal type II Na+/Pi cotransporter (NaPi-2) was investigated by expressing NaPi-2 in Xenopus laevis oocytes and applying the two-electrode voltage clamp. In the steady state, superfusion with inorganic phosphate (Pi) induced inward currents (Ip) in the presence of 96 mM Na+ over the potential range -140 </= V </= +40 mV. With Pi as the variable substrate, the apparent affinity constant (KmPi) was strongly dependent on Na+, increasing sixfold for a twofold reduction in external Na+. KmPi increased with depolarizing voltage and was more sensitive to voltage at reduced Na+. The Hill coefficient was close to unity and the predicted maximum Ip (Ipmax) was 40% smaller at 50 mM Na+. With Na+ as the variable substrate, KmNa was weakly dependent on both Pi and voltage, the Hill coefficient was close to 3 and Ipmax was independent of Pi at -50 mV. The competitive inhibitor phosphonoformic acid suppressed the steady state holding current in a Na+-dependent manner, indicating the existence of uncoupled Na+ slippage. Voltage steps induced pre-steady state relaxations typical for Na+-coupled cotransporters. NaPi-2-dependent relaxations were quantitated by a single, voltage-dependent exponential. At 96 mM Na+, a Boltzmann function was fit to the steady state charge distribution (Q-V) to give a midpoint voltage (V0.5) in the range -20 to -50 mV and an apparent valency of approximately 0.5 e-. V0.5 became more negative as Na+ was reduced. Pi suppressed relaxations in a dose-dependent manner, but had little effect on their voltage dependence. Reducing external pH shifted V0.5 to depolarizing potentials and suppressed relaxations in the absence of Na+, suggesting that protons interact with the unloaded carrier. These findings were incorporated into an ordered kinetic model whereby Na+ is the first and last substrate to bind, and the observed voltage dependence arises from the unloaded carrier and first Na+ binding step.

Animals↗

PubMed1997

Electrophysiological characterization of the flounder type II Na+/Pi cotransporter (NaPi-5) expressed in Xenopus laevis oocytes.

The two electrode voltage clamp technique was used to investigate the steady-state and presteady-state kinetic properties of the type II Na+/Pi cotransporter NaPi-5, cloned from the kidney of winter flounder (Pseudopleuronectes americanus) and expressed in Xenopus laevis oocytes. Steady-state Pi-induced currents had a voltage-independent apparent K(m) for Pi of 0.03 mM and a Hill coefficient of 1.0 at neutral pH, when superfusing with 96 mM Na+. The apparent K(m) for Na+ at 1 mM Pi was strongly voltage dependent (increasing from 32 mM at -70 mV to 77 mM at -30 mV) and the Hill coefficient was between 1 and 2, indicating cooperative binding of more than one Na+ ion. The maximum steady-state current was pH dependent, diminishing by 50% or more for a change from pH 7.8 to pH 6.3. Voltage jumps elicited presteady-state relaxations in the presence of 96 mM Na+ which were suppressed at saturating Pi (1 mM). Relaxations were absent in non-injected oocytes. Charge was balanced for equal positive and negative steps, saturated at extremes of potential and reversed at the holding potential. Fitting the charge transfer to a Boltzmann relationship typically gave a midpoint voltage (V0.5) close to zero and an apparent valency of approximately 0.6. The maximum steady-state transport rate correlated linearly with the maximum Pi-suppressed charge movement, indicating that the relaxations were NaPi-5-specific. The apparent transporter turnover was estimated as 35 sec-1. The voltage dependence of the relaxations was Pi-independent, whereas changes in Na+ shifted V0.5 to -60 mV at 25 mM Na+. Protons suppressed relaxations but contributed to no detectable charge movement in zero external Na+. The voltage dependent presteady-state behavior of NaPi-5 could be described by a 3 state model in which the partial reactions involving reorientation of the unloaded carrier and binding of Na+ contribute to transmembrane charge movement.

Animals↗

PubMed1995

Characterization of the osteoclast vacuolar H(+)-ATPase B-subunit.

During bone resorption, osteoclasts acidify the extracellular bone resorbing compartment via a vacuolar H(+)-ATPase (V-ATPase), which resides in the ruffled-border membrane. In an effort to characterize the composition of the osteoclast V-ATPase catalytic domain, we have isolated a cDNA clone that encodes the V-ATPase B-subunit from a cDNA library constructed from highly purified chicken osteoclasts. Comparison of the predicted amino-acid sequence with the published sequences of isoforms of V-ATPase B-subunits from other sources revealed that the chicken osteoclast B-subunit is brain type and not kidney type. Furthermore, only clones encoding the brain type isoform of subunit B could be generated by PCR from a cDNA library prepared from human osteoclastoma osteoclast-like cells. Northern blot analysis revealed that two B-subunit mRNAs, approx. 1.7 and 3.5 kb in length, are expressed in chicken bone marrow mono-nuclear cells, brain and kidney, although the relative amounts of these two transcripts were different in each tissue. In brain, the 3.5-kb mRNA was predominantly expressed. In bone marrow cells, the levels of the 1.7-kb mRNA were higher than in other tissues and expression of this message was increased by 1,25-dihydroxyvitamin D-3, suggesting that this mRNA is specifically upregulated during osteoclast differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1995

Alternative splicing generates a second isoform of the catalytic A subunit of the vacuolar H(+)-ATPase.

We have identified a second isoform of the catalytic A subunit of the vacuolar H+ pump in chicken osteoclasts. In this isoform (A2) a 72-bp cassette replaces a 90-bp cassette present in the classical A1 isoform. The A1-specific cassette encodes a region of the protein that contains one of the three ATP-binding consensus sequences (the P-loop) identified in this polypeptide, as well as the pharmacologically relevant Cys254. In contrast, the A2-specific cassette does not contain any of these features. These two isoforms, which appear to be ubiquitously expressed, are encoded by a single gene and are generated by alternative splicing of two mutually exclusive exons. The alternative RNA processing involves the recognition of a single site, the boundary between the A2- and A1-specific exons, as either acceptor (in A1) or donor (in A2) splice site.

Adenosine Triphosphate↗

PubMed1994

Nucleotide sequence of a cDNA for the beta 2 subunit isoform of Na+,K(+)-ATPase from human retina.

Using as probe the entire human liver cDNA clone coding for the beta 2 subunit isoform of the Na+,K(+)-ATPase, which lacks the initiation codon ATG, and the entire 5'-untranslated region (Martin-Vasallo, P., Dackowski, W., Emanuel, J.R. and Levenson, R. (1989) J. Biol. Chem. 264, 4613-4618), we isolated a larger clone from a directional human adult retina cDNA library (Swaroop, A. and Xu, J. (1993) Cytogenet. Cell Genet. 64, 292-294). This clone, pNH beta 2, shows 100% homology with the nucleotide sequence of the human liver cDNA clone and also contains additional 407 nucleotides in the 5'-untranslated region, the initiation codon and a poly(A) tail. Northern blot hybridization analysis reveals that the human mRNA (3.6 kb) is approx. 300 nucleotides larger than the major transcript size expressed in rat (3.3 kb). The larger human size mRNA for the human beta 2 Na+,K(+)-ATPase indicates species differences in gene processing.

Amino Acid Sequence↗

PubMed1994

cDNA from human ocular ciliary epithelium homologous to beta ig-h3 is preferentially expressed as an extracellular protein in the corneal epithelium.

The non-pigmented ciliary epithelium is largely responsible for the formation of aqueous humor in the mammalian eye. To provide a basis for studies at the molecular level, a directional expression cDNA library was constructed in Uni-ZAP XR vector from poly A+ RNA of the human non-pigmented ciliary epithelial derived ODM-2 cell line. Fifty-three cDNA clones were isolated from the library and characterized by partial sequence analysis. Approximately 49% of the clones exhibited homology with known genes in the GenBank/EMBL databases. The putative identification of these clones may reflect the transcriptional activity of the ODM-2 cells in culture. One of the identified clones, ODM-42-I, was found to be specific and highly expressed in the corneal epithelium. This clone had an exact match with a recently discovered human gene, beta ig-h3 (Skonier et al., 1992, DNA Cell Biol., 11:511-522), which codes a surface recognition protein, inducible by transforming growth factor beta (TGF-beta), and containing a putative binding site (RDG) for integrins. The ODM-42-I cDNA clone displays a distinctive pattern of expression found in the human eye, expressed almost exclusively in the cornea. Further studies, using sera from a synthetic peptide to the carboxy-terminal region of ODM-42-I, reveal that the protein is heterogeneous in charge and is preferentially expressed on the extracellular surface of corneal epithelial cells, and might share immunologic properties with integrins beta 1.

Animals↗

PubMed1993

Differential expression of the cellular retinaldehyde-binding protein in bovine ciliary epithelium.

Differential expression of the cellular retinaldehyde-binding protein (CRALBP), a likely component of the visual cycle, has been observed in the ocular ciliary epithelium, a bilayer of neurepithelial cells involved in the active transport of aqueous humor. Antibody probes raised to bovine ciliary epithelium were used to isolate a cDNA encoding CRALBP from a bovine ciliary epithelium cDNA expression library. Northern analysis of poly A+RNA isolated from three different regions of the neonate ciliary epithelium revealed a three-fold higher level of CRALBP expression in the most anterior portion of the pars plicata region relative to the posterior pars plana region. Western blot analysis using CRALBP-specific antibodies also demonstrated that the level of CRALBP expression was higher in the most anterior portion of the ciliary epithelium and gradually decreases toward the posterior region in both neonate and adult bovine eyes. Using indirect immunofluorescence and frozen-sectioned bovine ciliary epithelium, CRALBP was localized to the pigmented ciliary epithelial cell layer along the entire ciliary epithelium. In the nonpigmented ciliary epithelial cell layer, CRALBP was only detected in the pars plana region. Pigmented ciliary epithelial cells have also been cultured and CRALBP expression demonstrated for several continuous passages by Northern and Western analysis. These results raise questions regarding the physiological role of CRALBP in the ciliary epithelium and the involvement of the protein in the defining regional and functional boundaries with this tissue.

Animals↗

PubMed1993

Effect of extracellular volume expansion on erythrocyte cation transport in cirrhotic rats.

Erythrocyte intracellular Na+ and K+, and ouabain- and bumetanide-inhibitable Na+ efflux and 86Rb uptake have been measured in control and cirrhotic rats with or without extracellular volume expansion (EVE, saline, 3% body wt., 3 h). Non-expanded, cirrhotic rats showed a lower Na+ excretion (UNaV) than controls. After EVE, control rats showed a significantly higher UNaV (90%) and urinary flow (40%), than non-expanded controls. In cirrhotics, the increases in urinary flow (10%) and UNaV (17%) were not significant. No differences in intracellular Na+ and K+ levels between control and cirrhotic rats were observed. In controls none of these values changed with volume expansion, but in cirrhotic rats intracellular Na+ was significantly higher in expanded than in non-expanded rats. No differences in 86Rb uptake between non-expanded control and cirrhotic rats were observed. In controls EVE induced a decrease of pump-mediated 86Rb influx, but in cirrhotic rats, total and pump-mediated 86Rb influxes were lower in expanded than in non-expanded animals. By contrast, EVE induced a decrease in ouabain-inhibitable 86Rb uptake. In conclusion, in spite of the limitations imposed by considering the erythrocyte as representative of the renal cells, these results do not support an alteration in the response of the ouabain-inhibitable sodium pump as responsible for the lack of natriuretic response to extracellular volume expansion in cirrhotic rats. However, modification of the cotransport system in cirrhosis could play some role in this impaired response.

Animals↗

PubMed1992

Isolation of a cDNA encoding a glutathione S-transferase (GST) class-pi from the bovine ocular ciliary epithelium.

We have used a polyclonal antiserum to bovine ciliary epithelium, a secretory tissue involved in the formation of aqueous humor, to immunoscreen a directional lambda gt11 Sfi-Not cDNA expression library prepared from bovine ciliary epithelium poly(A)+ RNA. After immunoscreening 6 x 10(5) independent clones, 41 cDNA clones positive for ciliary epithelium were isolated and characterized. About one-third of the positive cDNA clones were found to be identical and to encode a glutathione S-transferase (GST) class-pi. The largest bovine GST cDNA clone isolated, pCN11, contains an open reading frame of 630 bases, encoding a protein of 210 amino acids with a calculated molecular weight of 23,335 Da. The corresponding amino acid sequence showed an overall identity of 85.6% with the human, and 85.2% with the rat and mouse GST class-pi. Northern analysis of bovine ocular tissues revealed that the GST class-pi gene encodes a 0.8-kilobase mRNA which is expressed most abundantly in cornea, ciliary epithelium and retina, and in lower levels in iris and lens. Cell lines derived from non-pigmented or pigmented bovine ciliary epithelium also showed high levels of GST-pi mRNA expression. These results provide additional evidence for differential gene expression of GST class-pi mRNA in various areas of the bovine eye.

Animals↗

PubMed1992

Molecular cloning of the bovine CD9 antigen from ocular ciliary epithelial cells.

The ciliary epithelium is a bilayer of epithelial cells responsible for the formation and secretion of aqueous humor in the mammalian eye. We have isolated a cDNA clone from a lambda gt11 cDNA library of bovine ocular ciliary epithelial cells encoding the CD9 antigen, a member of a new family of transmembrane proteins. The bovine CD9 clone contains an open reading frame of 226 amino acids (M(r) 24,860). The deduced amino acid sequence from the bovine CD9 cDNA clone shows 83.5% identity with the human counterpart isolated from megakaryocytes, and a lower degree of identity with a group of related antigens (TAPA-1, C0-029, CD53, MRC OX-44, ME491, CD63, CD37, and Sm23) involved in growth regulation. Analysis of bovine ocular tissues reveals that the CD9 gene encodes a 1.4 kb mRNA which is detectable predominantly in cornea and at low levels in ciliary epithelium, retina, iris, and lens. Normal and transformed cell lines established from the ocular ciliary epithelium exhibited significant levels of CD9 transcripts. These results raise questions regarding possible roles of CD9 in the anterior segment of the eye.

Amino Acid Sequence↗

PubMed1992

The osteoclast proton pump differs in its pharmacology and catalytic subunits from other vacuolar H(+)-ATPases.

Osteoclasts are multinucleated cells derived from the mononuclear phagocyte system in the hematopoietic bone marrow. Their function is to resorb bone during skeletal growth and remodeling. They perform this function by acidifying an enclosed extracellular space, the bone resorbing compartment. Analysis of proton transport by inside-out vesicles derived from highly purified chicken osteoclast membranes has revealed the presence of a novel type of multisubunit vacuolar-like H(+)-ATPase. Unlike H(+)-ATPases derived from any other cell type or organelle, proton transport and ATPase activity in osteoclast vesicles are sensitive to two classes of inhibitors, namely V-ATPase inhibitors [N-ethyl-maleimide (NEM) and bafilomycin A1] and vanadate (IC50 100 mumol l-1), an inhibitor previously found to affect only P-ATPases. The osteoclast V-ATPase morphologically resembles vacuolar proton pumps and contains several vacuolar-like subunits (115 x 10(3), 39 x 10(3) and 16 x 10(3)M(r)), demonstrated by Western blot analysis. Subunits A and B of the catalytic domain of the enzyme, however, differ from that of other V-ATPases. In osteoclasts, subunit A has an M(r) of 63 x 10(3) instead of 67 x 10(3)-70 x 10(3); in contrast, monocytes, macrophages and kidney microsomes, which contain a vanadate-insensitive H(+)-ATPase, express the classical subunit A (70 x 10(3)M(r)). Moreover, two types of 57 x 10(3)-60 x 10(3)M(r) B subunits are also found: they are differentially recognized by antibodies and one is expressed predominantly in osteoclasts and the other in bone marrow cells and in kidney microsomes. Preliminary cloning data have indicated that the B subunit expressed in osteoclasts may be similar to the brain isoform. The osteoclast proton pump may, therefore, constitute a novel class of V-ATPase, with a unique pharmacology and specific isoforms of two subunits in the catalytic portion of the enzyme.

Adenosine Triphosphatases↗

PubMed1991

Expression of multiple Na+,K(+)-ATPase genes reveals a gradient of isoforms along the nonpigmented ciliary epithelium: functional implications in aqueous humor secretion.

The Na+,K(+)-ATPase alpha 1, alpha 2, and alpha 3 subunit isoforms have been shown to be differentially expressed in the nonpigmented (NPE) and pigmented (PE) cells of the ocular ciliary epithelium (CE) (Martin-Vasallo et al., J. Cell. Physiol., 141:243-252, 1989; Ghosh et al., J. Biol. Chem., 265:2935-2940, 1990). In this study we analyzed and compared the pattern of expression of the multiple Na+,K(+)-ATPase alpha (alpha 1, alpha 2, alpha 3) subunit genes with the pattern of expression of the Na+,K(+)-ATPase beta (beta 1, beta 2) subunit genes along the bovine CE. We have selected three regions in the CE, referred to as 1) the anterior region of the pars plicata, near the iris; 2) the middle region of the pars plicata; and 3) the posterior region of the pars plana, near the ora serrata. Using isoform-specific cDNA probes and antibodies for the Na+,K(+)-ATPase alpha 1, alpha 2, alpha 3, beta 1, and beta 2 subunits on Northern and Western blot analysis, we found that mRNA and polypeptides are expressed in all three CE regions with different abundance. The pattern of expression of alpha and beta isoforms detected along the NPE cell layers suggests a gradient of alpha 1, alpha 2, alpha 3, beta 1, and beta 2 mRNAs and polypeptides that correlates with decreasing Na+,K(+)-ATPase activity from the most anterior region at the pars plicata towards the posterior region at the ora serrata. We also found marked differences in the pattern of immunolocalization of Na+,K(+)-ATPase alpha 1, alpha 2, alpha 3, beta 1, and beta 2 subunit isoforms in different regions of the CE. In the anterior region, NPE cells stained intensely at the basal lateral membrane with specific monoclonal and polyclonal antibodies for each of the alpha (alpha 1, alpha 2, alpha 3) and beta (beta 1, beta 2) Na,K-ATPase isoforms. In the middle and posterior regions of the CE, NPE cells showed lower or absent levels of staining with alpha 1, alpha 2, alpha 3, and beta 1 antibodies, although staining with beta 2 was abundant. In contrast, PE cells throughout the CE were stained at the basal lateral membrane by antibodies to alpha 1 and beta 1, while no staining signals were detected with the rest of the antibodies (i.e. alpha 2, alpha 3, and beta 2). Our results support the conclusion that the three alpha and two beta isoforms of the Na+,K(+)-ATPase are differentially expressed in the two cell layers that make up the CE.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Renal transplantation and red blood cell sodium transport: role of prednisone treatment.

This study assesses the role of prednisone and endogenous digoxin-like immunoreactivity (EDLI) in the increased Na+ pump activity in renal allograft patients. Red blood cell (RBC) Na+ transport activities and plasma concentrations of EDLI were measured in ten controls and ten renal allograft recipients (5 hypertensive) while undergoing treatment with cyclosporin, prednisone, and azathioprine, and also after prednisone withdrawal. As compared to controls, prednisone-treated patients showed an increased Na+ pump activity (0.323/h vs 0.571, P less than 0.05) and decreased RBC Na+ concentration (6.69 mM vs 4.99, P less than 0.05). They also showed a decrease in the activity of cotransport, countertransport, and passive Na+ efflux (0.02/h vs 0.005, P less than 0.05; 207 mumol/l vs 35, P less than 0.05; 0.02/h vs 0.005 respectively, P less than 0.05). After prednisone withdrawal, normotensive and hypertensive patients showed RBC Na+ transport system activities and RBC Na+ concentration similar to those of controls. EDLI was not detected in controls or in patients. We conclude that prednisone treatment increased the Na+ pump activity, and decreased the RBC Na+ concentration. Moreover, it induced a decrease in the activity of secondary RBC Na+ transport systems. This study provides no evidence for a modulatory role of EDLI in the RBC Na+ pump activity. Neither parameters can be presumed to be a marker of hypertension in these patients.

Adult↗

PubMed1990

Effect of extracellular volume expansion on erythrocyte sodium transport in rats.

The effects of extracellular volume expansion (EVE) on the major sodium transport systems and sodium and potassium contents in rat erythrocytes have been examined in the present study. Study has been performed in anesthetized Wistar rat weighing about 300 g. Acute extracellular volume expansion (EVE) was induced by a constant intravenous saline infusion (3% body wt, 3 hours). Rats anaesthetized and catheterized but not expanded were used as controls. Arterial blood samples from control and expanded rats were obtained at the same time, and assayed immediately. Intracellular sodium and potassium concentration and ouabain sensitive (Na(+)-K(+)-pump) and bumetanide sensitive (Na(+)-K(+)-cotransport system) outward Na+ fluxes in erythrocytes were measured. The effect of plasma on erythrocyte transport was also analyzed by measuring 86Rb uptake. Neither of two plasma cations (Na+ and K+) were modified by the EVE. Also intracellular Na+ and K+ levels remained unvariable. Total Na+ efflux was not modified by EVE, but pump-mediated Na+ efflux was smaller after than before EVE. The ouabain-inhibible Na+ efflux rate constant decreased after EVE (from 687 +/- 81 to 525 +/- 29 h-1 x 10(-3); P less than 0.05). Both Na(+)-K(+)cotransport-mediated Na+ efflux and passive permeability increased significantly after EVE. The incubation with plasma from saline-infused animals induced a significant decrease in Rb uptake rate constant, that was not observed after incubation with plasma from non-expanded rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Endogenous digoxin-like immunoreactivity and erythrocyte sodium transport in uraemic patients undergoing dialysis.

1. Erythrocyte Na+ transport (Na+ pump activity, co-transport, countertransport and passive Na+ efflux) and intracellular Na+ concentration were studied in 10 normal individuals and in 29 uraemic patients on chronic haemodialysis, before and after a haemodialysis session. Eight of them fulfilled the criteria of hypertension. 2. Normotensive patients before haemodialysis were classified in two groups: group 1 (pump-) with decreased erythrocyte Na+ pump activity, and group 2 (normal pump) with normal erythrocyte Na+ pump activity. Group 1 showed, compared with controls, a normal intracellular Na+ concentration and a decreased co-transport, but no difference in either countertransport or passive Na+ efflux. After haemodialysis this difference disappeared. Before haemodialysis, group 2 showed a high intracellular Na+ concentration, but activities of the Na+ transport systems studied were similar to those of controls. After haemodialysis, cell Na+ concentration decreased to a level not significantly different from that of controls. 3. Both before and after haemodialysis, hypertensive patients showed Na+ transport system activities and an intracellular Na+ concentration similar to those of controls. 4. Endogenous digoxin-like immunoreactivity (EDLI) and erythrocyte Na+ transport were studied in five normotensive and five hypertensive patients, before and after haemodialysis. EDLI in plasma was similar in both groups before and after haemodialysis. No correlation was found between EDLI and erythrocyte Na+ pump activity. 5. These results suggest the existence in some dialysed uraemic patients of alterations in erythrocyte Na+ fluxes, which may be corrected by haemodialysis. EDLI and erythrocyte Na+ fluxes do not seem to be markers of secondary hypertension in these patients.

Adult↗

PubMed1988

Absence of an endogenous regulator of Na+,K+-ATPase activity in the tissues of cirrhotic rats.

Microsomal Na+,K+-ATPase isolated from the renal cortex of rats with CCL4-induced cirrhosis (CIR) showed a higher specific activity than the enzyme obtained from control rats (COR). Kinetic studies showed a lower K0.5 for ATP (0.08 +/- 0.03 vs. 0.24 +/- 0.04 mM; p less than 0.05), a lower Na+ activation constant (9.6 +/- 1.5 vs. 19.0 +/- 1.7 mM; p less than 0.05), and a higher K+ activation constant (1.2 +/- 0.1 vs. 0.6 +/- 0.1 mM; p less than 0.05) for CIR. The optimal pH of the enzyme was 0.5 units higher in CIR than COR. The fluorescence of eosin-treated enzymes indicated a higher ratio of E1/E2 forms of Na+,K+-ATPase in CIR. The K+-activated p-nitrophenylphosphatase (pNPPase) activity of the enzyme was lower in CIR than COR rats (1.5 +/- 0.1 vs. 2.2 +/- 0.1 mU/mg; p less than 0.05). Dialysing (24 h) COR microsomes reproduced most of the changes observed in CIR enzymes (kinetics, optimal pH, and eosin fluorescence). Lyophilized dialysate of COR, but not of CIR microsomes, inhibits Na+,K+-ATPase activity. These results suggest that a dialysable inhibitor modifies the Na+,K+-ATPase activity in the kidney of COR which is almost absent in that of CIR. The absence of this factor may lead to the overall inability to excrete Na+ in the cirrhotic state.

Animals↗