Publications (23)163.61 Total impact
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Article: Loop disorders: insights derived from defined genotypes.
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ABSTRACT: Great progress has been made in the last 15 years in the characterization and the pathophysiological understanding of renal salt and water wasting associated with inherited disorders of the thick ascending limb (TAL) of Henle's loop, the loop disorders. Besides careful clinical observations and innovative physiological concepts, molecular genetics have made this progress possible. So far, mutations in five different genes may be responsible for the loop disorders. These gene products are as follows: NKCC2 symporter, ROMK, ClC-Ka, ClC-Kb, and barttin, a β-subunit to both chloride channels. The key symptoms, such as polyhydramnios secondary to fetal polyuria, postnatal volume depletion with hypotension, iso- or hyposthenuria, hyperprostaglandinuria and hypercalciuria followed by hypokalemic alkalosis secondary to hyperaldosteronism, are typical features of loop disorders that are restricted to TAL, such as in disorders with NKCC2 and ROMK mutations. However, transient perinatal hyperkalemia in infants with ROMK mutations suggests an additional function of ROMK for K secretion in the cortical collecting duct. The extremely rare human ClC-Kamutation has only been described in combination with ClC-Kb mutations. Similar to barttin mutations, this double knockout of transepithelial salt transport in TAL and in distal convoluted tubule (DCT) leads to a severe loop disorder with deafness. In contrast, the isolated ClC-Kb mutation predominantly appears as an incomplete loop disorder with features similar to an isolated DCT defect, because ClC-Kb function in TAL can in part be compensated by ClC-Ka. This compensation does not exist in DCT. Besides these defined genotypes, the type and the severity of mutation as well as the onset and quality of medical care are important determinants for the patients' outcome. Considering a few variables, such as transient hyperkalemia, disease onset beyond neonatal period, profound hypochloremia and hypokalemia, or congenital hearing loss, might be helpful to guide genetic testing efficiently.Nephron Physiology 01/2011; 118(1):p7-14. · 2.55 Impact Factor -
Article: Evaluating PVALB as a candidate gene for SLC12A3-negative cases of Gitelman's syndrome.
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ABSTRACT: Loss-of-function mutations in SLC12A3 coding for the thiazide-sensitive NaCl cotransporter (NCC) cause Gitelman's syndrome (GS), a recessively inherited salt-losing tubulopathy. Most GS patients are compound heterozygous. However, up to 30% of GS patients carry only a single mutant allele, and a normal SLC12A3 screening is also observed in a small subset of patients. Locus heterogeneity could explain the lack of detection of mutant SLC12A3 alleles in GS patients. The renal phenotype of the parvalbumin knockout mice pointed to PVALB as a candidate gene for GS for SLC12A3-negative cases. PCR and direct sequencing of PVALB was performed in 132 GS patients in whom only one or no (N = 79) mutant SLC12A3 allele was found. The possible interference of biallelic SNPs (single nucleotide polymorphisms) on normal transcription or normal splicing was investigated. Genotyping of 110 anonymous blood donors was performed to determine the allelic frequency in the normal population. No sequence variants resulting in amino acid substitution or truncated protein within the PVALB gene were found in the 264 chromosomes tested. Ten biallelic SNPs, including six novel polymorphisms, were identified: five in the 5' UTR, none of them affecting predicted regulatory elements; three in the coding region, without alteration of the consensus splice sites, and two in the 3' UTR. The observed allelic frequencies did not differ significantly between GS patients and controls. Our results strongly suggest that mutations in the PVALB gene are not involved in GS patients who harbour a single or no mutant SLC12A3 allele.Nephrology Dialysis Transplantation 06/2008; 23(10):3120-5. · 3.40 Impact Factor -
Article: Can renal tubular hypokalemic disorders be accurately diagnosed on the basis of the diuretic response to thiazide?
Nature Clinical Practice Nephrology 11/2007; 3(10):528-9. · 6.08 Impact Factor -
Article: Late-onset manifestation of antenatal Bartter syndrome as a result of residual function of the mutated renal Na+-K+-2Cl- co-transporter.
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ABSTRACT: Genetic defects of the Na+-K+-2Cl- (NKCC2) sodium potassium chloride co-transporter result in severe, prenatal-onset renal salt wasting accompanied by polyhydramnios, prematurity, and life-threatening hypovolemia of the neonate (antenatal Bartter syndrome or hyperprostaglandin E syndrome). Herein are described two brothers who presented with hyperuricemia, mild metabolic alkalosis, low serum potassium levels, and bilateral medullary nephrocalcinosis at the ages of 13 and 15 yr. Impaired function of sodium chloride reabsorption along the thick ascending limb of Henle's loop was deduced from a reduced increase in diuresis and urinary chloride excretion upon application of furosemide. Molecular genetic analysis revealed that the brothers were compound heterozygotes for mutations in the SLC12A1 gene coding for the NKCC2 co-transporter. Functional analysis of the mutated rat NKCC2 protein by tracer-flux assays after heterologous expression in Xenopus oocytes revealed significant residual transport activity of the NKCC2 p.F177Y mutant construct in contrast to no activity of the NKCC2-D918fs frameshift mutant construct. However, coexpression of the two mutants was not significantly different from that of NKCC2-F177Y alone or wild type. Membrane expression of NKCC2-F177Y as determined by luminometric surface quantification was not significantly different from wild-type protein, pointing to an intrinsic partial transport defect caused by the p.F177Y mutation. The partial function of NKCC2-F177Y, which is not negatively affected by NKCC2-D918fs, therefore explains a mild and late-onset phenotype and for the first time establishes a mild phenotype-associated SLC12A1 gene mutation.Journal of the American Society of Nephrology 09/2006; 17(8):2136-42. · 9.66 Impact Factor -
Article: Influence of gain of function epithelial chloride channel ClC-Kb mutation on hearing thresholds.
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ABSTRACT: Hearing depends on functional ClC-K-type chloride channels composed of barttin with ClC-Ka or ClC-Kb. Loss-of-function mutations of the barttin gene BSND or of both, the ClC-Ka gene CLNKA and the ClC-Kb gene CLNKB lead to congenital deafness and renal salt wasting. Recently, we identified the gain-of-function mutation ClC-Kb(T481S) which is associated with increased blood pressure. To explore the impact of ClC-Kb(T481S) on hearing, healthy volunteers (n=329) and individuals suffering from tinnitus (n=246) volunteered for hearing tests (n=348) and genetic analysis (n=575). 19.1% of the individuals were heterozygote (ClC-Kb(T481S)/ClC-Kb) and 1.7% homozygote carriers. Pure tone average hearing threshold (PTAt) for air conduction was significantly (p<0.033) lower in ClC-Kb(T481S) carriers (13.2+/-1.2dB) than in wild-type individuals (17.1+/-0.9dB). The prevalence of ClC-Kb(T481S) carriers was significantly increased (29.7%) in individuals with PTAt<15dB (p<0.05) and significantly decreased (13.2%) in individuals with PTAt>30 dB (p<0.017). The difference was largely due to the female population. Bone conduction was less affected pointing to an effect of the mutation on middle ear function. Tinnitus tended to be more frequent in ClC-Kb(T481S) carriers, a difference, however, not statistically significant. In conclusion, hearing thresholds are slightly lower in carriers of ClC-Kb(T481S), i.e., the gain-of-function polymorphism ClC-Kb(T481S) exerts a subtle but significant protective effect against hearing loss.Hearing Research 04/2006; 214(1-2):68-75. · 2.70 Impact Factor -
Article: A Spanish founder mutation in the chloride channel gene, CLCNKB, as a cause of atypical Bartter syndrome in adult age.
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ABSTRACT: Mutations in the chloride channel gene, CLCNKB, usually cause classic Bartter syndrome (cBS) or a mixed Bartter-Gitelman phenotype in the first years of life. We report an adult woman with atypical BS caused by a homozygous missense mutation, A204T, in the CLCNKB gene, which has previously been described as the apparently unique cause of cBS in Spain. The evaluation of this patient revealed an overlap of phenotypic features ranging from severe biochemical and systemic disturbances typical of cBS to scarce symptoms and diagnosis in the adult age typical of Gitelman syndrome. The tubular disease caused a dramatic effect on mental, growth and puberal development leading to low IQ, final short stature and abnormal ovarian function. Furthermore, low serum PTH concentrations with concomitant nephrocalcinosis and normocalcaemia were observed. Both ovarian function and serum PTH levels were normalized after treatment with cyclooxygenase inhibitors. The present report confirms a weak genotype-phenotype correlation in patients with CLCNKB mutations and supports the founder effect of the A204T mutation in Spain. In our country, the genetic diagnosis of adult patients with hereditary hypokalaemic tubulopathies should include a screening of A204T mutation in the CLCNKB gene.Hormone Research 02/2006; 65(2):62-8. · 2.48 Impact Factor -
Article: Response: ClC-Kb Mutation Revisited.
Hypertension 02/2006; · 6.21 Impact Factor -
Article: CLCN5 mutation (R347X) associated with hypokalaemic metabolic alkalosis in a Turkish child: an unusual presentation of Dent's disease.
Nephrology Dialysis Transplantation 08/2005; 20(7):1476-9. · 3.40 Impact Factor -
Article: Salt handling in the distal nephron: lessons learned from inherited human disorders.
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ABSTRACT: The molecular basis of inherited salt-losing tubular disorders with secondary hypokalemia has become much clearer in the past two decades. Two distinct segments along the nephron turned out to be affected, the thick ascending limb of Henle's loop and the distal convoluted tubule, accounting for two major clinical phenotypes, hyperprostaglandin E syndrome and Bartter-Gitelman syndrome. To date, inactivating mutations have been detected in six different genes encoding for proteins involved in renal transepithelial salt transport. Careful examination of genetically defined patients ("human knockouts") allowed us to determine the individual role of a specific protein and its contribution to the overall process of renal salt reabsorption. The recent generation of several genetically engineered mouse models that are deficient in orthologous genes further enabled us to compare the human phenotype with the animal models, revealing some unexpected interspecies differences. As the first line treatment in hyperprostaglandin E syndrome includes cyclooxygenase inhibitors, we propose some hypotheses about the mysterious role of PGE(2) in the etiology of renal salt-losing disorders.AJP Regulatory Integrative and Comparative Physiology 05/2005; 288(4):R782-95. · 3.34 Impact Factor -
Article: pH dependence of extracellular calcium sensing receptor activity determined by a novel technique.
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ABSTRACT: Increasing evidence points to the role of the extracellular Calcium Sensing Receptor (CaSR) as a multimodal receptor responding to diverse physiologic stimuli, such as extracellular divalent and polyvalent cations, amino acids, and ionic strength. Within the kidney, these stimuli converge on the CaSR to coordinate systemic calcium and water homeostasis. In this process, the impact of urinary pH changes on the activity of the CaSR has not yet been defined. We therefore performed the present study to analyze the pH sensitivity of the CaSR. To assess the activation state of the CaSR, we developed a new method based on the functional coupling between CaSR activity and gating of calcium sensitive potassium currents mediated by SK4 potassium channels. Two-electrode voltage clamping was used to determine whole cell currents in Xenopus oocytes heterologously expressing rat CaSR and rat SK4 potassium channels. Coexpression of CaSR and SK4 gave rise to potassium currents that were dependent on CaSR-mediated intracellular calcium release, and thereby corresponded to the activation state of the CaSR. In presence of extracellular calcium, ambient alkalinization above pH 7.5 increased CaSR activity. Evaluation of the CaSR calcium sensitivity at various ambient proton concentrations revealed that this effect was due to a sensitization of the CaSR towards extracellular calcium. Coexpression with SK4 potassium channels provides a fast and sensitive approach to evaluate CaSR activity in Xenopus oocytes. As disclosed by this novel technique, CaSR activity is regulated by extracellular pH.Kidney International 02/2005; 67(1):187-92. · 6.61 Impact Factor -
Article: Activating mutation of the renal epithelial chloride channel ClC-Kb predisposing to hypertension.
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ABSTRACT: The chloride channel ClC-Kb is expressed in the basolateral cell membrane of the distal nephron and participates in renal NaCl reabsorption. Loss-of-function mutations of ClC-Kb lead to classic Bartter syndrome, a rare salt-wasting disorder. Recently, we identified the ClC-Kb(T481S) polymorphism, which confers a strong gain-of-function effect on the ClC-Kb chloride channel. The present study has been performed to explore the prevalence of the mutation and its functional significance in renal salt handling and blood pressure regulation. As evident from electrophysiological analysis with the 2-electrode voltage-clamp technique, heterologous expression of ClC-Kb(T481S) in Xenopus oocytes gave rise to a current that was 7-fold larger than the current produced by wild-type ClC-Kb. The prevalence of the mutant allele was significantly higher in an African population from Ghana (22%) than in whites (12%). As tested in 1 white population, carriers of ClC-Kb(T481S) were associated with significantly higher systolic (by approximately 6.0 mm Hg) and diastolic (by approximately 4.2 mm Hg) blood pressures and significantly higher prevalence (45% versus 25%) of hypertensive (> or =140/90 mm Hg) blood pressure levels. Individuals carrying ClC-Kb(T481S) had significantly higher plasma Na+ concentrations and significantly decreased glomerular filtration rate. In conclusion, the mutation ClC-Kb(T481S) of the renal epithelial Cl- channel ClC-Kb strongly activates ClC-Kb chloride channel function in vitro and may predispose to the development of essential hypertension in vivo.Hypertension 07/2004; 43(6):1175-81. · 6.21 Impact Factor -
Article: Salt wasting and deafness resulting from mutations in two chloride channels.
New England Journal of Medicine 04/2004; 350(13):1314-9. · 53.30 Impact Factor -
Article: A common sequence variation of the CLCNKB gene strongly activates ClC-Kb chloride channel activity.
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ABSTRACT: Tubular transepithelial reabsorption of chloride along the nephron is a major determinant of body salt and water homeostasis and blood pressure regulation. About 40% of the glomerulary filtered sodium chloride are reabsorbed in the distal nephrons. Vectorial transepithelial sodium chloride transport is critically dependent on the function of basolateral ClC-K type chloride channels there. Modulation of ClC-Kb chloride channel activity by polymorphic variations of the CLCNKB gene, thus, could form a molecular basis for salt sensitivity of blood pressure regulation. In this study we tested the effect of several polymorphic variants on ClC-Kb chloride channel activity. After heterologous expression in Xenopus oocytes, ClC-Kb channel activity and surface expression in presence of the ClC-K beta subunit barttin were determined by two-electrode voltage-clamp analysis, immunofluorescence, and ClC-Kb surface enzyme-linked immunosorbent assay (ELISA). Chloride currents induced by the ClC-Kb variants L27R, G214A, I419V, T562M, and E578K were not significantly different from wild-type currents. The ClC-KbT481S variation, however, which showed a frequency of 20% in our control population, dramatically activated chloride conductance by a factor of 20. Activation of chloride currents was also observed after introducing homologous mutations in ClC-Ka and ClC-K1, but not in ClC-2 and ClC-5 chloride channels. ClC-Kb activation by the T481S mutation did not change intrinsic ion channel pore properties and did not require increased surface expression of ClC-KbT481S. Genetic heterogeneity of ClC-Kb chloride channels correlates with functional heterogeneity, which assigns ClC-Kb to a set of genes potentially relevant for polygenic salt-sensitivity of blood pressure regulation.Kidney International 02/2004; 65(1):190-7. · 6.61 Impact Factor -
Article: A new mutation (intron 9 +1 G>T) in the SLC12A3 gene is linked to Gitelman syndrome in Gypsies.
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ABSTRACT: Gitel syndrome is an inherited tubular disorder characterized by metabolic alkalosis, hypokalemia, and hypomagnesemia of renal origin and hypocalciuria. The majority of patients with Gitelman syndrome carry inactivating mutations in the SLC12A3 gene encoding the sodium-chloride cotransporter located in the distal convoluted tubule. The purpose of this study was to investigate the underlying mutation in Gitelman syndrome patients of Gypsy race from different geographic origin. Twenty Gypsy patients with clinical and biochemical features of Gitelman syndrome were investigated by mutational analysis. The patients belonged to 12 unrelated Gypsy families living in four different European countries. The parents and unaffected siblings of each patient, as well as the DNA of a population of 200 healthy control patients, were also analyzed. All patients were homozygous for the same splice site mutation, guanine to thymine in the first position of intron 9 of SLC12A3 gene. This mutation was not found in the control population. Parents were heterozygous for the mutation. Despite sharing a common mutation, the clinical manifestations of the syndrome in the patients varied from lack of symptoms in six children to severe growth retardation in four. Demonstration of a novel point mutation within the SLC12A3 gene in our cohort of Gypsy families with Gitelman syndrome is highly suggestive of a founder effect. This finding will facilitate the identification of the genetic defect in further cases of Gitelman syndrome among the Gypsy population. Our study represents the largest series ever published of patients with Gitelman syndrome having the same underlying mutation, and supports the lack of correlation between genotype and clinical phenotype in this disease.Kidney International 02/2004; 65(1):25-9. · 6.61 Impact Factor -
Article: Classification and rescue of ROMK mutations underlying hyperprostaglandin E syndrome/antenatal Bartter syndrome.
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ABSTRACT: Mutations in the renal K+ channel ROMK (Kir 1.1) cause hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), a severe tubular disorder leading to renal salt and water wasting. Several studies confirmed the predominance of alterations of current properties in ROMK mutants. However, in most of these studies, analysis was restricted to nonmammalian cells and electrophysiologic methods. Therefore, for the majority of ROMK mutations, disturbances in protein trafficking remained unclear. The aim of the present study was the evaluation of different pathogenic mechanisms of 20 naturally occurring ROMK mutations with consecutive classification into mutational classes and identification of distinct rescue mechanisms according to the underlying defect. Mutated ROMK potassium channels were expressed in Xenopus oocytes and a human kidney cell line and analyzed by two electrode voltage clamp analysis, immunofluorescence, and Western blot analysis. We identified 14 out of 20 ROMK mutations that did not reach the cell surface, indicating defective membrane trafficking. High expression levels rescued six out of 14 ROMK mutants, leading to significant K+ currents. In addition, two early inframe stop mutations could be rescued by aminoglycosides, resulting in full-length ROMK and correct trafficking to the plasma membrane in a subset of transfected cells. In contrast to previous reports, most of the investigated ROMK mutations displayed a trafficking defect that might be rescued by pharmacologic agents acting as molecular chaperones. The evaluation of different disease-causing mechanisms will be essential for establishing new and more specific therapeutic strategies for HPS/aBS patients.Kidney International 10/2003; 64(3):923-32. · 6.61 Impact Factor -
Article: Classification and rescue of ROMK mutations underlying hyperprostaglandin E syndrome/antenatal Bartter syndrome
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ABSTRACT: Classification and rescue of ROMK mutations underlying hyperprostaglandin E syndrome/antenatal Bartter syndrome.Background Mutations in the renal K+ channel ROMK (Kir 1.1) cause hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), a severe tubular disorder leading to renal salt and water wasting. Several studies confirmed the predominance of alterations of current properties in ROMK mutants. However, in most of these studies, analysis was restricted to nonmammalian cells and electrophysiologic methods. Therefore, for the majority of ROMK mutations, disturbances in protein trafficking remained unclear. The aim of the present study was the evaluation of different pathogenic mechanisms of 20 naturally occurring ROMK mutations with consecutive classification into mutational classes and identification of distinct rescue mechanisms according to the underlying defect.Kidney International 08/2003; 64(3):923-932. · 6.61 Impact Factor -
Article: Transient neonatal hyperkalemia in the antenatal (ROMK defective) Bartter syndrome.
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ABSTRACT: Identification of neonatal hyperkalemia as a complication of Bartter syndrome (BS), a disorder usually characterized by hypokalemic metabolic alkalosis. Study design Case-series description of a group of 12 infants with mutations in the renal potassium channel ROMK, causing one of the antenatal variants of BS. Prematurity, postnatal polyuria, and dehydration were seen in all cases. Plasma potassium was as high as 9.0 +/- 1.2 mmol/L and sodium as low as 124 +/- 3.5 mmol/L, appearing usually at day 3 of life and normalizing by the end of the first postnatal week. No hyperkalemia was found in 12 neonates with the variant of BS and deafness. The mean plasma potassium level during the first week of life among a group of very low-birth-weight infants with similar relative azotemia was 4.9 +/- 1 mmol/L (P <.001). The postneonatal period in the ROMK-defective children with BS was characterized by failure to thrive, hypercalciuria, nephrocalcinosis, and minimal-to-no hypokalemia. Early postnatal hyperkalemia, sometimes severe, may complicate antenatal BS associated with ROMK mutations. Its association with hyponatremia and hyperreninemic hyperaldosteronism may erroneously suggest the diagnosis of pseudohypoaldosteronism type 1. The expression of ROMK in both the thick ascending limb and cortical collecting duct may explain this apparently tubular maturation phenomenon.Journal of Pediatrics 03/2003; 142(3):318-23. · 4.11 Impact Factor -
Article: Role of cyclooxygenase-2 in hyperprostaglandin E syndrome/antenatal Bartter syndrome.
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ABSTRACT: Hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS) is a congenital salt-losing tubulopathy with an induced expression of cyclooxygenase-2 (COX-2) in the macula densa probably leading to hyperreninemia. Inhibition of stimulated prostaglandin E2 (PGE2) formation with indomethacin results in a significant improvement of clinical symptoms and is therefore standard therapy. Using the COX-2 selective inhibitor rofecoxib, we investigated the role of COX-2 in the pathophysiology of HPS/aBS. Six clinically well-characterized patients with HPS/aBS (3 girls) were enrolled into the study. Four patients had mutations in the renal potassium channel ROMK, one patient in the furosemide-sensitive cotransporter NKCC2, whereas in one patient no molecular abnormality could be detected. Median age was 15.8 years (range: 9.1 to 19.0 years). Patients were evaluated on indomethacin treatment, 3 days after indomethacin withdrawal, and after 4 days of treatment with rofecoxib. Therapeutic drug monitoring was performed. COX-2-selectivity of rofecoxib was confirmed in vivo and ex vivo. Both indomethacin and rofecoxib ameliorated clinical symptoms, the typical laboratory findings, and significantly suppressed PGE2 and PGE-M excretion to normal values while it was elevated under withdrawal conditions. Rofecoxib suppressed hyperreninemia to a similar extent as indomethacin. In patients with HPS/aBS, excessive PGE2 synthesis and hyperreninemia is dependent on COX-2 activity. This observation proves the stimulatory role of COX-2 on renin-secretion in salt-depletion in humans. Clinical long-term efficacy and potential side effects of rofecoxib need to be evaluated in a larger cohort of HPS/aBS-patients.Kidney International 08/2002; 62(1):253-60. · 6.61 Impact Factor -
Article: Barttin increases surface expression and changes current properties of ClC-K channels.
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ABSTRACT: The term Bartter syndrome encompasses a heterogeneous group of autosomal recessive salt-losing nephropathies that are caused by disturbed transepithelial sodium chloride reabsorption in the distal nephron. Mutations have been identified in the NKCC2 (Na(+)-K(+)-2Cl(-)) cotransporter and ROMK potassium channel, which cooperate in the process of apical sodium chloride uptake, and ClC-Kb chloride channels, which mediate basolateral chloride release. Recently, mutations in barttin, a protein not related to any known ion transporter or channel, were described in BSND, a variant of Bartter syndrome associated with sensorineural deafness. Here we show that barttin functions as an activator of ClC-K chloride channels. Expression of barttin together with ClC-K in Xenopus oocytes increased ClC-K current amplitude, changed ClC-K biophysical properties, and enhanced ClC-K abundance in the cell membrane. Co-immunoprecipitation revealed a direct interaction of barttin with ClC-K. We performed in situ hybridization on rat kidney slices and RT-PCR analysis on microdissected nephron segments to prove co-expression of barttin, ClC-K1 and ClC-K2 along the distal nephron. Functional analysis of BSND-associated point mutations revealed impaired ClC-K activation by barttin. The results demonstrate regulation of a CLC chloride channel by an accessory protein and indicate that ClC-K activation by barttin is required for adequate tubular salt reabsorption.Pflügers Archiv - European Journal of Physiology 07/2002; 444(3):411-8. · 4.46 Impact Factor -
Article: Heteroligomerization of an Aquaporin-2 mutant with wild-type Aquaporin-2 and their misrouting to late endosomes/lysosomes explains dominant nephrogenic diabetes insipidus.
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ABSTRACT: Autosomal nephrogenic diabetes insipidus (NDI), a disease in which the kidney is unable to concentrate urine in response to vasopressin, is caused by mutations in the Aquaporin-2 (AQP2) gene. Analysis of a new family with dominant NDI revealed a single nucleotide deletion (727deltaG) in one AQP2 allele, which encoded an AQP2 mutant with an altered and extended C-terminal tail. When expressed in oocytes, the tetrameric AQP2-727deltaG was retained within the cell. When co-expressed, AQP2-727deltaG, but not a mutant in recessive NDI (AQP2-R187C), formed hetero-oligomers with wild-type (wt) AQP2 and reduced the water permeability of these oocytes, because of a reduced plasma membrane expression of wt-AQP2. Expressed in renal epithelial cells, AQP2-727deltaG predominantly localized to the basolateral membrane and late endosomes/lysosomes, whereas wt-AQP2 was expressed in the apical membrane. Upon co-expressing in these cells, wt-AQP2 and AQP2-727deltaG mainly co-localized to late endosomes/lysosomes. In conclusion, hetero-oligomerization of AQP2-727deltaG with wt-AQP2 and consequent mistargeting of this complex to late endosomes/lysosomes results in absence of AQP2 in the apical membrane, which can explain dominant NDI in this family. Together with other mutants in dominant NDI, our data reveal that a misrouting, instead of a lack of function, is a general mechanism for the 'loss of function' phenotype in dominant NDI and visualizes for the first time a mislocalization of a wild-type protein to late endosomes/lysosomes in polarized cells after oligomerization with a mutant protein.Human Molecular Genetics 05/2002; 11(7):779-89. · 7.64 Impact Factor
Top co-authors
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Institutions
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2002–2011
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Philipps-Universität Marburg
Marburg an der Lahn, Hesse, Germany
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2006
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Hospital Universitario Fundacion Alcorcon
Madrid, Madrid, Spain -
Eberhard-Karls-Universität Tübingen
Tübingen, Baden-Wuerttemberg, Germany
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