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I Zelikovic

Publications and source records attributed to I Zelikovic.

At least 19 recordsLinked to original sources
PubMed2001

Proline transport in MDCK cells expressing a mutant regulatory subunit of cAMP-dependent protein kinase.

cAMP-dependent protein kinase (cAK) regulates the activity of several membrane-bound ion channels and carriers. The role of cAK in regulating the transport of osmoprotective amino acids in the distal tubule is unknown. We examined the regulation of Na(+)- and Cl(-)-dependent proline transport in MDCK cells expressing a mutant murine regulatory subunit (RIalpha(AB)) of cAK. For this purpose, MDCK cells were transfected with an expression vector encoding RIalpha(AB) driven by the metallothionein 1 promoter together with neomycin-resistance (NEO) gene. Stable G418-resistant colonies were isolated that expressed RIalpha(AB) as demonstrated by Northern hybridization analysis using a cDNA probe for RIalpha and cAK assay that showed decreased enzyme activity. A clone constitutively expressing high levels of RIalpha(AB) (M(AB)) in a Zn-independent manner and a control clone transfected with the NEO gene alone (M(neo)) were selected for transport studies. We examined the effect of the cAMP-stimulating agents forskolin (F) and IBMX on NaCl-dependent uptake of [(3)H]proline by confluent monolayers of transfected MDCK cells. While F/IBMX-induced mean inhibition of proline transport in M(neo) cells was 48 and 45% at 5 and 15 min, respectively, inhibition of proline uptake in M(AB) cells was 9% (5 min) and 0% (15 min). These data demonstrate that the inhibition of NaCl-linked proline transport in response to elevated cAMP is reversed in MDCK clones that express mutant cAK and provide evidence that cAK mediates the modulatory action of cAMP on proline transport. cAK may play an important role in controlling transport of proline and other osmoprotective amino acids in the renal tubule.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Plasmapheresis in a very young infant with atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome (HUS) is a heterogeneous group of disorders, the pathogenesis of which is unclear. Plasma transfusions and plasmapheresis are widely used modes of therapy for adults with this life-threatening syndrome. There is very limited experience in using plasmapheresis therapy in children and infants with atypical HUS. Plasmapheresis, which is considered a relatively safe procedure in adults and older children, may be hazardous in neonates and very young infants and can result in severe complications. We report a 2-month-old infant with idiopathic atypical HUS, who was successfully treated with a 1-month course of plasmapheresis during the acute phase of the disease. Appropriate preparations as well as several adjustments were made in order to meet the special needs of this very young infant who, to the best of our knowledge, is the youngest reported patient with atypical HUS to undergo plasmapheresis. Plasmapheresis therapy of the infant was not associated with any complications of the procedure and resulted in marked clinical improvement. We conclude that plasmapheresis in neonates and in very small infants is technically feasible, can be performed without major complications, and may be of benefit in individual cases.

Feasibility Studies↗
PubMed2001

Molecular pathophysiology of tubular transport disorders.

Inherited tubular transport disorders comprise a group of diseases that lead to profound derangements in the homeostasis of electrolytes, minerals, or organic solutes in the body. In the past decade remarkable progress has been made in our understanding of the molecular pathogenesis of hereditary tubulopathies and the fundamental molecular physiology of renal tubular transport processes. This review summarizes hereditary diseases caused by mutations in genes encoding transporter or channel proteins operating along the renal tubule. Review of the molecular basis of hereditary tubulopathies reveals various loss-of-function or gain-of-function mutations in genes encoding cotransporter, exchanger, or channel proteins, which are located in the luminal, basolateral, or endosomal membranes of the tubular cell or in paracellular tight junctions. These gene mutations result in a variety of functional defects in transporter/channel proteins, including decreased activity, impaired gating, defective trafficking, impaired endocytosis and degradation, or defective assembly of channel subunits. Further molecular studies of inherited tubular transport disorders may shed more light on the molecular pathophysiology of these diseases and may significantly improve our understanding of the mechanisms underlying renal salt homeostasis, urinary mineral excretion, and blood pressure regulation in health and disease. The identification of the molecular defects in inherited tubulopathies may provide a basis for future design of targeted therapeutic interventions and, possibly, strategies for gene therapy of these complex disorders.

Biological Transport↗
PubMed2001

CAMP-dependent protein kinase inhibits proline transport across the rat renal tubular brush border membrane.

Very little is known about the cellular mechanisms controlling renal tubular amino acid transport. cAMP-dependent protein kinase (cAK) modulates the activity of several ion channels and pumps in biological membranes. The direct influence of cAK on transmembrane amino acid transport has not been investigated. We studied the effect the cAKmediated phosphorylation on Na+ and Cl(-)-linked proline transport across the rat renal brush border membrane (BBM). cAK bioassay and Western hybridization analysis using cAK subunit-specific antibodies demonstrated the presence of the enzyme in the BBM. Brush border membrane vesicles (BBMV) were phosphorylated using the "hyposmotic shock" technique. cAMP, by activating endogenous cAK,and exogenous, highly purified catalytic subunit of cAK inhibited NaCl-dependent proline transport by phosphorylated, lysed/resealed BBMV compared with control vesicles. The cAK-mediated inhibition of proline uptake was completely abolished when phosphorylation at the cytoplasmic (inner side) of the membrane was prevented by isosmotic, rather than hyposmotic, phosphorylation. The cAK-induced inhibition of proline transport was reversed by the specific cAK inhibitor peptide, PK1. These data suggest that cAMP-dependent protein kinase-mediated phosphorylation modulates Na+(-) and Cl(-)-linked proline transport across the tubular luminal membrane.

Animals↗
PubMed1999

Cl- and membrane potential dependence of amino acid transport across the rat renal brush border membrane.

The relative roles of the anion present and the membrane potential in the operation of each of the seven amino acid transport systems in the renal tubular brush border membrane were explored by manipulating transmembrane potential and chemical gradients across the membrane. The effect of various external anions with different permeabilities of the membrane and of valinomycin-generated K+ diffusion potential on Na+-coupled amino acid accumulation by rat renal brush border membrane vesicles was examined. Accumulation of all amino acids examined, except for cystine, was membrane potential dependent. The highest voltage dependence was observed for taurine (equivalent to glucose) and l-methionine. Addition of taurine uptake values obtained under each electrical gradient (inside negative) and a chemical gradient (100 mM NaCl out) condition yielded markedly lower values than under conditions where there was a combined electrochemical gradient. Cl- gradient rather than merely imposing a voltage gradient was a specific mediator of Na+-coupled transport of l-proline, taurine, l-glutamic acid, and glycine across the brush border membrane. Cl- gradient alone under Na+-equilibrated conditions could energize an overshoot of taurine accumulation by vesicles providing evidence that taurine is energetically activated by and coupled to Cl- transport. These data suggest that Na+-linked transport of most amino acids across the tubular luminal membrane is an electrogenic positive process and for proline, taurine, glutamic acid, and glycine, a Cl--requiring process. A negative intracellular potential combined with luminal chloride is required for optimal Na+-coupled transport of these amino acids across the luminal membrane of the proximal tubule. The coupling of Cl- to the transport of these osmoprotective amino acids may enhance their volume regulatory effect in kidney cells and other mammalian cells.

Amino Acids↗
PubMed1999

Natural history of fetal simple renal cysts detected in early pregnancy.

PURPOSE: In this 12-year prospective, longitudinal study we investigated the natural history of fetal simple renal cysts identified by ultrasonography in early pregnancy. MATERIALS AND METHOD: A detailed sonographic examination of the fetus was performed between January 1987 and June 1998 in 29,984 consecutive pregnancies at 14 to 16 weeks of gestation. Amniocenteses and chromosomal investigations were done in all cases in which a simple renal cyst was detected in the fetus. Followup sonography was done in all cases of renal cyst during pregnancy, infancy and, when indicated, childhood. RESULTS: Simple renal cysts were diagnosed at 14 to 16 weeks of gestation in 28 fetuses (1/1,100 pregnancies, 0.09%). In 25 fetuses the cysts resolved during pregnancy. In 2 fetuses the cysts remained benign but persisted postnatally and in 1 a renal cyst that was initially defined as simple was the first sign of unilateral multicystic dysplastic kidney. Except for nonseptated cystic hygroma in 1 fetus, none of the others had associated anomalies of the urinary or other organ systems and no chromosomal anomalies. Postnatal followup in all cases revealed healthy children. CONCLUSIONS: A fetal simple renal cyst can be identified by ultrasonography in early pregnancy. In the absence of associated anatomical or chromosomal abnormalities, the majority of cysts will resolve during pregnancy without any sequelae. Given the transient nature of most fetal simple renal cysts detected in early pregnancy, it is possible that these cysts represent a distinct entity within the spectrum of cystic kidney diseases.

Female↗
PubMed1998

Cholelithiasis following Escherichia coli O157:H7-associated hemolytic uremic syndrome.

Sequelae of Escherichia coli O157:H7-associated hemolytic uremic syndrome (HUS) 2-3 years following an outbreak in Washington State have been prospectively studied to identify predictors of adverse sequelae. Logistic regression analysis was used to examine associations between findings in the acute course and long-term renal and gastrointestinal outcomes. Twenty-one percent of patients had gastrointestinal sequelae, which included cholelithiasis resulting in cholecystectomy (3/29), persistent pancreatitis (2/29), late colon stricture (1/29), and/or glucose intolerance (1/29). Logistic regression analysis found long-term gastrointestinal sequelae were higher in patients who, during HUS, had hypertension [odds ratio (OR) = 21.2, 95% confidence interval (CI) = 1.9-164.4, P = 0.01] or gastrointestinal complications (OR = 21.2, 95% CI = 1.9-164.4, P = 0.01). Renal sequelae were seen in 35% of patients. One patient (4%) had persistent hypertension and 9 (31%) had minor urinary findings (hematuria or proteinuria). Thrombocytopenia lasting longer than 10 days during the acute illness was associated with a risk for subsequent renal sequelae (OR = 15.0, 95% CI = 1.98-1,703.0, P = 0.009). We conclude a high incidence of gastrointestinal sequelae, especially cholelithiasis presenting long after the acute illness, may be seen with HUS. The short follow-up period may underestimate the extent and severity of eventual renal sequelae.

Child↗
PubMed1995

Ca(2+)-dependent protein kinases modulate proline transport across the renal brush-border membrane.

The cellular mechanisms controlling reabsorption of amino acids in the renal proximal tubule are unknown. Ca(2+)-dependent protein kinases modulate the activity of several ion channels and carriers in the kidney. The role of these enzymes in regulating tubular amino acid transport has not been established. We investigated the effect of Ca(2+)- and phospholipid-dependent protein kinase C (PKC) and Ca2+/calmodulin-dependent protein kinase II (CaMK II) on Na(+)- and Cl(-)-dependent proline transport across the rat renal brush-border membrane (BBM). Bioassays utilizing selective peptide substrates for Ca(2+)-dependent protein kinases demonstrated the presence of PKC and CaMK II in the BBM. Renal brush-border membrane vesicles (BBMV) were phosphorylated using the "hyposmotic shock" technique. Endogenous (membrane-bound) CaMK II and PKC, as well as exogenous, highly purified PKC inhibited NaCl-linked proline uptake by phosphorylated, lysed/resealed BBMV compared with control vesicles. The inhibitory effect of Ca2+ on proline transport, without the presence of other kinase activators, was mediated by activation of endogenous CaMK II. The CaMK II- and PKC-induced inhibition of proline uptake was reversed by the specific kinase inhibitor peptides CaMK II-(281-302) and PKC-(19-31), respectively. These data suggest that Ca(2+)-dependent protein kinase-mediated phosphorylation inhibits NaCl-dependent proline transport across the tubular luminal membrane.

Animals↗
PubMed1994

Escherichia coli O 157:H7-associated hemolytic-uremic syndrome after ingestion of contaminated hamburgers.

We conducted a retrospective analysis of 37 children with Escherichia coli O157:H7-associated hemolytic-uremic syndrome. The infection was traced to contaminated hamburgers at a fast-food restaurant chain. Within 5 days of the first confirmed case, the Washington State Department of Health identified the source and interrupted transmission of infection. Ninety-five percent of the children initially had severe hemorrhagic colitis. Nineteen patients (51%) had significant extrarenal abnormalities, including pancreatitis, colonic necrosis, glucose intolerance, coma, stroke, seizures, myocardial dysfunction, pericardial effusions, adult respiratory disease syndrome, and pleural effusions. Three deaths occurred, each in children with severe multisystem disease. At follow-up two children have significant impairment of renal function (glomerular filtration rate < 80 ml/min/per 1.73 Hm2); both of these children have a normal serum creatinine concentration. Hemolytic-uremic syndrome is the most common cause of acute renal failure in children, and this experience emphasizes the systemic nature of this disease. Clinicians should anticipate that multisystem involvement may occur in these patients, necessitating acute intervention or chronic follow-up. This outbreak of Hemolytic-uremic syndrome also highlights the microbiologic hazards of inadequately prepared food and emphasizes the importance of public health intervention in controlling Hemolytic-uremic syndrome.

Adolescent↗
PubMed1993

Renal amino acid transport: cellular and molecular events from clearance studies to frog eggs.

This article reviews recent advances in the mechanisms of renal amino acid transport. Renal amino acid transport is necessary to efficiently reclaim approximately 450 mmol amino acids from the glomerular ultrafiltrate each day in man. In general, individual amino acids are transported across the epithelial membrane of the proximal tubule by a sodium (Na+) dependent mechanism. This cotransport process utilizes the energy of the Na+ gradient to enter the cell. The amino acid then exits the basolateral surface and Na+ is pumped out by the Na(+)-K(+)-ATPase located in the basolateral membrane. In addition to the cellular accumulation of amino acids across the luminal membrane, these compounds may be taken up by the cell from the basolateral surface. Most amino acids are transported both individually and in a series of seven group specific processes. Human disorders of amino acid transport have been described for six of the seven transport systems. The process of ontogeny of amino acid accumulation by the proximal tubule is a complex one and will be further discussed in this review. A number of factors including pH, ion dependency, electrogenicity of transport process, as well as a variety of hormonal factors, may contribute to the regulation of amino acid transport. Gene expression of several amino acid transporters has been successfully performed using the oocyte of the frog Xenopus laevis. Using this system, a number of transporters have been cloned. Such a strategy will permit the cloning of virtually all transporter molecules, and thus we can anticipate the elucidation of the structure of the transporters. However, for a comprehensive understanding of cytoskeletal interactions protein phosphorylation and phospholipid domains and their linkage to the primary structure of the transporter need to be studied. The future for research in this area is indeed a bright one.

Amino Acid Metabolism, Inborn Errors↗
PubMed1993

The role of protein phosphorylation in renal amino acid transport.

Changes in tubular reabsorption of amino acids and other solutes are characteristic of the immature renal tubule and of various hereditary nephropathies. The cellular mechanisms governing these aberrations in renal amino acid transport have not been established. Calcium (Ca2+)-dependent protein kinases are known to phosphorylate membrane-bound carrier proteins, thereby modulating transport of various solutes by the proximal tubule. The role of these enzymes in regulating renal tubular amino acid transport, particularly during kidney development, is unknown. We investigated: (1) the effect of Ca(2+)- and phospholipid-dependent protein kinase [protein kinase C (PKC)] and Ca2+/calmodulin-dependent protein kinase II (CaMKII) on sodium chloride (NaCl)-linked proline transport by renal brush border membrane vesicles (BBMV) from adult rats using the "hypoosmotic shock" technique (lysis of vesicles); (2) the activity, expression and subcellular distribution (cytosol, particulate, BBM) of Ca(2+)-dependent protein kinases in kidneys from 7-day-old and adult rats using MBP 4-14 and autocamtide II phosphorylation assays for PKC and CaMKII, respectively, endogenous protein phosphorylation (using gel electrophoresis and autoradiography) and Western immunoblot analysis to detect PKC and CaMKII. The studies showed: (1) endogenous (membrane-bound) CaMKII and PKC as well as exogenous, highly purified PKC inhibit proline uptake by phosphorylated, lyzed/resealed BBMV when compared with control vesicles; the voltage-clamped, nonelectrogenic component of proline transport was inhibited by PKC- but not CaMKII-mediated phosphorylation; (2) a Ca(2+)-dependent activity of both kinases was evident in all subcellular fractions tested in immature and adult kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Urinary tract infections in children. An update.

Urinary tract infection is a common and frequently recurring condition in children. The susceptibility of the host, the presence of urinary tract abnormalities, and the virulence of the urinary pathogens are of primary importance in the development of the infection. Renal parenchymal scarring, hypertension, and renal insufficiency are well-established complications of the infection in children. To reduce the risk of renal damage, diagnosis and treatment must be prompt. The diagnosis demands radiologic evaluation of the urinary tract in all boys, all children younger than 5 years, all patients with voiding dysfunction, and school-aged girls with recurrent infection to identify those patients with vesicoureteral reflux, obstruction, or other urinary tract abnormalities. Both voiding cystourethrography and renal ultrasonography are the initial examinations to use to determine the next appropriate study. Children with vesicoureteral reflux or with recurrent urinary tract infections should receive prophylactic antibiotic therapy and should be observed closely to prevent renal scarring.

Anti-Bacterial Agents↗
PubMed1991

Developmental maturation of Na(+)-H+ exchange in rat renal tubular brush-border membrane.

The developmental maturation of the Na(+)-H+ exchanger present in the proximal tubular luminal membrane of the rat was investigated. An overshoot of 1 mM Na+ uptake was evident in brush-border membrane vesicles derived from the renal cortex of 7- and 21-day-old and adult rats in the presence of an outwardly directed H+ concentration ([H+]) gradient [intravesicular pH (pHi) = 5.5; extravesicular pH (pHo) = 7.5]. Na+ uptake was amiloride sensitive at all ages examined. Significantly higher initial rate (3 s) Na+ uptake and peak accumulation (60 s) in the presence of a [H+] gradient were found in vesicles from 7-day-old rats compared with adult animals. Significantly enhanced initial rate Na+ uptake by neonatal vesicles was also evident under pH-equilibrated conditions (pHi = pHo = 7.5). An age-related decrease in amiloride-sensitive Na+ accumulation by vesicles was found. Kinetic analysis of Na(+)-H+ exchange in voltage-clamped vesicles, in the presence of dimethylamiloride (DMA), and calculating 5-s Na+ uptake values showed a maturational decrease in capacity (decreasing Vmax) coupled with a maturational increase in affinity (decreasing Km) of Na(+)-H+ antiport. These data suggest that an enhanced amiloride-inhibitable Na(+)-H+ exchange activity due to increased capacity of exchange exists in the proximal tubular luminal membrane of the neonatal rat. This increased Na(+)-H+ exchange may potentially contribute to positive Na+ balance in the growing organism and may rapidly dissipate the electrochemical Na+ gradient across the luminal membrane necessary for Na(+)-solute contransport, thereby contributing to glycosuria and aminoaciduria of early life.

Aging↗
PubMed1991

Chloride and membrane potential dependence of sodium ion-proline symport.

Proline accumulation by renal proximal tubule brush border membrane vesicles is Na+ dependent, but little is known about the role of anions or membrane potential on proline uptake. Recent studies in a variety of transport systems, including rat renal brush border membrane vesicles, indicate that halide anions chloride (Cl-) and bromide (Br-) are essential for glycine, beta-alanine, gamma-aminobutyric acid, and taurine uptake, so the possibility that Na(+)-proline symport is Cl- dependent was explored. Also, the role of membrane potential on transport was assessed by determining the effect of external anions with different membrane permeabilities. The ratio of initial rate Cl- stimulated to thiocyanate (SCN)(-)-stimulated uptake values serves to measure Cl- dependence. The initial rate of proline uptake to equilibrium value was 3.11 +/- 0.5 (SE) in the presence of Cl- versus SCN-. The ratio for D-glucose, whose uptake is governed only by electrogenic status of the membrane, was 0.61 +/- 0.47 (P less than 0.001 versus proline). In another series of experiments, uptake values for various anions as a percent of equilibrium (I/E x 100) were: SCN-, 84.9 +/- 10.9; NO3, 49.9 +/- 11.0; SO4(2-), 27.3 +/- 4.4; F-, 68.5 +/- 18.3; Cl-, 164.1 +/- 44.6; Br-, 150.6 +/- 30.2; I-, 56.7 +/- 13.5. The stoichiometry of uptake by Hill plot analysis of proline uptake in the presence of varying concentrations of Na+ (0 to 100 mM) and Cl- (0 to 100 mM) was 2Na+:1Cl-:1 proline.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Transport Systems, Neutral↗
PubMed1990

The renal transport of taurine and the regulation of renal sodium-chloride-dependent transporter activity.

A model for the beta-amino acid taurine transport is presented to help define the ionic, pH, and voltage requirements for the movement of taurine into the rat proximal tubule brush border membrane vesicle (BBMV). Sodium-(Na+)-taurine symport across the apical surface of the proximal tubule has a highly specific requirement for Cl- and Br-. Active taurine transport operates with a 2 Na+:1 Cl-:1 taurine-carrier complex. Complexes like the one required for maximal taurine transport may be pertinent for many other amino acids whose uptake is Na(+)-dependent. Renal epithelial cell lines LLC-PK and MDCK were used to define the nature of taurine uptake; they express Na(+)-Cl(-)-taurine cotransport that is inhibited by beta-alanine. The cell lines up- or down-regulate taurine transport in response to changes in the taurine concentration of the medium in a manner similar to that seen in BBMV. The adaptation is present by 12 h and depends on new protein synthesis and protein import to the cell membrane. The role of trafficking in the adaptive response was also explored in brush border vesicles. During dietary surfeit, transporter could be down-regulated and transporters could be shifted back into the microtubule system, resulting in taurinuria. Use of continuous renal cell lines allowed a more mechanistic exploration of intracellular trafficking in the up- and down-expression of the Na(+)-Cl(-)-taurine cotransporter. Colchicine appeared to be a more potent inhibitor of the rapid (over hours) adaptive response to a reduction in media and, therefore, intracellular taurine content.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗