PubMed Health⌕ Search

Biomedical subjects

Pascal Houillier

Publications and source records attributed to Pascal Houillier.

At least 19 recordsLinked to original sources
PubMed2006

Acute growth hormone administration induces antidiuretic and antinatriuretic effects and increases phosphorylation of NKCC2.

Growth hormone (GH) has antidiuretic and antinatriuretic effects in rats and humans, but the molecular mechanisms responsible for these effects are unknown. The aim of this study was to investigate the mechanisms behind the acute renal effects of GH in rats. Female rats received rat (r)GH (2.8 mg/kg sc) or saline and were placed in metabolic cages for 5 h. Urinary excretion of electrolytes and urinary volume were reduced after rGH injection, while urine osmolality was increased. Creatinine and lithium clearance remained unchanged, suggesting that rGH increases reabsorption in segments distal to the proximal tubule. Total plasma insulin-like growth factor I (IGF-I) levels did not change, while cortical IGF-I mRNA abundance was increased. The relative abundance of total and Ser(256)-phosphorylated aquaporin 2 was found to be unchanged by immunoblotting, whereas a significant increase of Thr(96) and Thr(101)-phosphorylated NKCC2 (renal Na(+), K(+), 2Cl(-) cotransporter) was found in the inner stripe of outer medulla thick ascending limbs (mTAL). Additionally, an increased NKCC2 expression was observed in the cortical region. Immunohistochemistry confirmed these findings. The density of NKCC2 molecules in the apical membrane of mTAL cells appeared to be unchanged after rGH injection evaluated by immunoelectron microscopy. Basolateral addition of rGH or IGF-I to microperfused rat mTAL segments did not change transepithelial voltage. In conclusion, GH appears to exert its acute antinatriuretic and antidiuretic effects through indirect activation of NKCC2 in the mTAL.

Animals↗
PubMed2006

Tissue kallikrein stimulates Ca(2+) reabsorption via PKC-dependent plasma membrane accumulation of TRPV5.

The transient receptor potential vanilloid 5 (TRPV5) channel determines urinary Ca(2+) excretion, and is therefore critical for Ca(2+) homeostasis. Interestingly, mice lacking the serine protease tissue kallikrein (TK) exhibit robust hypercalciuria comparable to the Ca(2+) leak in TRPV5 knockout mice. Here, we delineated the molecular mechanism through which TK stimulates Ca(2+) reabsorption. Using TRPV5-expressing primary cultures of renal Ca(2+)-transporting epithelial cells, we showed that TK activates Ca(2+) reabsorption. The stimulatory effect of TK was mimicked by bradykinin (BK) and could be reversed by application of JE049, a BK receptor type 2 antagonist. A cell permeable analog of DAG increased TRPV5 activity within 30 min via protein kinase C activation of the channel since mutation of TRPV5 at the putative PKC phosphorylation sites S299 and S654 prevented the stimulatory effect of TK. Cell surface labeling revealed that TK enhances the amount of wild-type TRPV5 channels, but not of the TRPV5 S299A and S654A mutants, at the plasma membrane by delaying its retrieval. In conclusion, TK stimulates Ca(2+) reabsorption via the BK-activated PLC/DAG/PKC pathway and the subsequent stabilization of the TRPV5 channel at the plasma membrane.

Amino Acid Substitution↗
PubMed2006

Genetic investigation of autosomal recessive distal renal tubular acidosis: evidence for early sensorineural hearing loss associated with mutations in the ATP6V0A4 gene.

Mutations in the ATP6V1B1 and ATP6V0A4 genes, encoding subunits B1 and 4 of apical H(+) ATPase, cause recessive forms of distal renal tubular acidosis (dRTA). ATP6V1B mutations have been associated with early sensorineural hearing loss (SNHL), whereas ATP6V0A4 mutations are classically associated with either late-onset SNHL or normal hearing. The phenotype and genotype of 39 new kindreds with recessive dRTA, 18 of whom were consanguineous, were assessed. Novel and known loss-of-function mutations were identified in 31 kindreds. Fourteen new and five recurrent mutations of the ATP6V0A4 gene were identified in 21 families. For the ATP6V1B1 gene, two new and two previously described mutations were identified in 10 families. Surprisingly, seven probands with ATP6V0A4 gene mutations developed severe early SNHL between the ages of 2 mo and 10 yr. No mutation was detected in eight families. These data extend the spectrum of disease-causing mutations and provide evidence for genetic heterogeneity in SNHL. The data also demonstrate that mutations in either of these genes may cause early deafness, and they highlight the importance of genetic screening for recessive forms of dRTA independent of hearing status.

Acidosis, Renal Tubular↗
PubMed2005

How Bartter's and Gitelman's syndromes, and Dent's disease have provided important insights into the function of three renal chloride channels: ClC-Ka/b and ClC-5.

Chloride channels are expressed in almost all cell membranes and are potentially involved in a wide variety of functions. The kidney expresses 8 of the 9 chloride channels of the ClC family that have been cloned so far to date in mammals. This review focuses on the pathophysiology of two renal disorders that have contributed recently to our understanding of the physiological role of chloride channels belonging to the ClC family. First are the related syndromes of Bartter's and Gitelman's, in which inactivating mutations of the genes encoding either of the ClC-Ks, or their regulatory beta-subunit barttin, have shown the important contribution of these chloride channels to renal tubular sodium and chloride (NaCl) transport along the loop of Henle and distal tubule. Second is the renal Fanconi syndrome known as Dent's disease, in which ClC-5 disruption has revealed the key role of this endosomal chloride channel in the megalin-mediated endocytotic pathway in the proximal tubule. The underlying pathophysiology of this inherited disorder demonstrates how ClC-5 is directly or indirectly required for the reabsorption of filtered low-molecular-weight proteins and bioactive peptides, also expression of membrane transporters, and clearance of calcium-based stone-forming crystals.

Animals↗
PubMed2005

Tissue kallikrein-deficient mice display a defect in renal tubular calcium absorption.

Renal tubular calcium (RTCa) transport is one of the main factors that determine serum Ca concentration and urinary Ca excretion. The distal convoluted and connecting tubules reabsorb a significant fraction (10%) of filtered Ca. These tubule segments also synthesize in large abundance tissue kallikrein (TK), a major kinin-forming enzyme. Tested was the hypothesis that TK and kinins are involved in controlling RTCa transport by studying TK (TK-/-) or kinin B2 receptor (B2-/-)-deficient mice on different Ca diets. On a 0.9% wt/wt Ca diet, 129Sv or C57Bl/6 TK-/- mice excreted significantly more Ca in urine than their wild-type (WT) littermates. There was no difference between TK-/- and WT mice for plasma concentrations of Ca, Mg, creatinine, parathyroid hormone, or 1,25-dihydroxyvitamin D. On a low Ca (LCa) diet (0.01% wt/wt), urinary Ca excretion decreased in both TK-/- and WT mice but still remained higher in TK-/- mice compared with WT. The plasma Ca concentration was unchanged in C57Bl/6 TK-/- mice but decreased significantly in 129Sv TK-/- mice. Taken together, these data demonstrate that TK deficiency led to impaired RTCa absorption. On the LCa diet, renal TK gene expression doubled in WT mice. No change in urinary Ca excretion was observed in B2-/- mice, even after treatment with a kinin B1-receptor antagonist, and these mice adapted normally to the LCa diet. TK deficiency had no effect on the renal abundance of distal Ca transporter mRNA. These data suggest that TK may be a physiologic regulator of RTCa transport, acting through a non-kinin-mediated mechanism.

Analysis of Variance↗
PubMed2005

Genetic ablation of Rhbg in the mouse does not impair renal ammonium excretion.

NH(4)(+) transport by the distal nephron and NH(4)(+) detoxification by the liver are critical for achieving regulation of acid-base balance and to avoid hyperammonemic hepatic encephalopathy, respectively. Therefore, it has been proposed that rhesus type B glycoprotein (Rhbg), a member of the Mep/Amt/Rh NH(3) channel superfamily, may be involved in some forms of distal tubular acidosis and congenital hyperammonemia. We have tested this hypothesis by inactivating the RHbg gene in the mouse by insertional mutagenesis. Histochemical studies analyses confirmed that RHbg knockout (KO) mice did not express Rhbg protein. Under basal conditions, the KO mice did not exhibit encephalopathy and survived well. They did not exhibit hallmarks of distal tubular acidosis because neither acid-base status, serum potassium concentration, nor bone mineral density was altered by RHbg disruption. They did not have hyperammonemia or disturbed hepatic NH(3) metabolism. Moreover, the KO mice adapted to a chronic acid-loading challenge by increasing urinary NH(4)(+) excretion as well as their wild-type controls. Finally, transepithelial NH(3) diffusive permeability, or NH(3) and NH(4)(+) entry across the basolateral membrane of cortical collecting duct cells, measured by in vitro microperfusion of collecting duct from KO and wild-type mice, was identical with no apparent effect of the absence of Rhbg protein. We conclude that Rhbg is not a critical determinant of NH(4)(+) excretion by the kidney and of NH(4)(+) detoxification by the liver in vivo.

Acidosis, Renal Tubular↗
PubMed2005

Bone status in primary hyperparathyroidism assessed by regional bone mineral density from the whole body scan and QUS imaging at calcaneus.

To assess the bone mineral density status in primary hyperparathyroidism (PHPT), we studied 64 females with PHPT and 17 healthy women. Regional BMD (arms, trunk, legs) from the whole body scan and conventional sites (lumbar spine, femur, radius) were assessed by DXA. Quantitative ultrasound (QUS) imaging measurements were performed at calcaneus. Sixteen women had history of renal lithiasis, 11 had low impact fracture and 37 women had neither renal lithiasis nor fracture. In the entire group, the mean Z-scores were significantly decreased at all sites (lumbar spine, femur, radius). In all clinical subgroups, the mean Z-scores were significantly decreased at radius. The mean Z-scores in premenopausal women were significantly decreased comparatively to postmenopausal women at lumbar spine and femur. In a group of PHPT females matched to controls for age and BMI, only BMD values at radius were lower in PHPT patients than in control (P < 0.03). However, from the whole body scan data, all sites but no trunk were significantly involved in PHPT patients (P < 0.04). Using QUS measurements at calcaneus, the BUA but not SOS in PHPT females was significantly lower (P = 0.03) than in controls. Our results suggest that low BMD at lumbar spine and femur is encountered preferentially in premenopausal women. The BMD decrease predominates at limbs in PHPT with presumably a gradient from proximal to distal part of the limbs. Indeed, the distal part of the limbs are the most affected areas in PHPT whatever the amount of cortical or trabecular bone.

Absorptiometry, Photon↗
PubMed2005

Predictive performance of the modification of diet in renal disease and Cockcroft-Gault equations for estimating renal function.

Recent recommendations emphasize the need to assess kidney function using creatinine-based predictive equations to optimize the care of patients with chronic kidney disease. The most widely used equations are the Cockcroft-Gault (CG) and the simplified Modification of Diet in Renal Disease (MDRD) formulas. However, they still need to be validated in large samples of subjects, including large non-U.S. cohorts. Renal clearance of (51)Cr-EDTA was compared with GFR estimated using either the CG equation or the MDRD formula in a cohort of 2095 adult Europeans (863 female and 1232 male; median age, 53.2 yr; median measured GFR, 59.8 ml/min per 1.73 m(2)). When the entire study population was considered, the CG and MDRD equations showed very limited bias. They overestimated measured GFR by 1.94 ml/min per 1.73 m(2) and underestimated it by 0.99 ml/min per 1.73 m(2), respectively. However, analysis of subgroups defined by age, gender, body mass index, and GFR level showed that the biases of the two formulas could be much larger in selected populations. Furthermore, analysis of the SD of the mean difference between estimated and measured GFR showed that both formulas lacked precision; the CG formula was less precise than the MDRD one in most cases. In the whole study population, the SD was 15.1 and 13.5 ml/min per 1.73 m(2) for the CG and MDRD formulas, respectively. Finally, 29.2 and 32.4% of subjects were misclassified when the CG and MDRD formulas were used to categorize subjects according to the Kidney Disease Outcomes Quality Initiative chronic kidney disease classification, respectively.

Adult↗
PubMed2004

Inactivation of the Na-Cl co-transporter (NCC) gene is associated with high BMD through both renal and bone mechanisms: analysis of patients with Gitelman syndrome and Ncc null mice.

UNLABELLED: Chronic thiazide treatment is associated with high BMD. We report that patients and mice with null mutations in the thiazide-sensitive NaCl cotransporter (NCC) have higher renal tubular Ca reabsorption, higher BMD, and lower bone remodeling than controls, as well as abnormalities in Ca metabolism, mainly caused by Mg depletion. INTRODUCTION: Chronic thiazide treatment decreases urinary Ca excretion (UVCa) and increases BMD. To understand the underlying mechanisms, Ca and bone metabolism were studied in two models of genetic inactivation of the thiazide-sensitive NaCl cotransporter (NCC): patients with Gitelman syndrome (GS) and Ncc knockout (Ncc(-/-)) mice. MATERIALS AND METHODS: Ca metabolism was analyzed in GS patients and Ncc(-/-) mice under conditions of low dietary Ca. BMD was measured by DXA in patients and mice, and bone histomorphometry was analyzed in mice. RESULTS: GS patients had low plasma Mg. They exhibited reduced UVCa, but similar serum Ca and GFR as control subjects, suggesting increased renal Ca reabsorption. Blood PTH was lower despite lower serum ionized Ca, and Mg repletion almost corrected both relative hypoparathyroidism and low UVCa. BMD was significantly increased in GS patients at both lumbar (+7%) and femoral (+16%) sites, and osteocalcin was reduced. In Ncc(-/-) mice, serum Ca and GFR were unchanged, but UVCa was reduced and PTH was elevated; Mg repletion largely corrected both abnormalities. Trabecular and cortical BMD were higher than in Ncc(+/+) mice (+4% and +5%, respectively), and despite elevated PTH, were associated with higher cortical thickness and lower endosteal osteoclastic surface. CONCLUSIONS: Higher BMD is observed in GS patients and Ncc(-/-) mice. Relative hypoparathyroidism (human) and bone resistance to PTH (mice), mainly caused by Mg depletion, can explain the low bone remodeling and normal/low serum Ca despite increased renal Ca reabsorption.

Adolescent↗
PubMed2004

Angiotensin II inhibits NaCl absorption in the rat medullary thick ascending limb.

NaCl reabsorption in the medullary thick ascending limb of Henle (MTALH) contributes to NaCl balance and is also responsible for the creation of medullary interstitial hypertonicity. Despite the presence of angiotensin II subtype 1 (AT(1)) receptors in both the luminal and the basolateral plasma membranes of MTALH cells, no information is available on the effect of angiotensin II on NaCl reabsorption in MTALH and, furthermore, on angiotensin II-dependent medullary interstitial osmolality. MTALHs from male Sprague-Dawley rats were isolated and microperfused in vitro; transepithelial net chloride absorption (J(Cl)) as well as transepithelial voltage (V(te)) were measured. Luminal or peritubular 10(-11) and 10(-10) M angiotensin II had no effect on J(Cl) or V(te). However, 10(-8) M luminal or peritubular angiotensin II reversibly decreased both J(Cl) and V(te). The effect of both luminal and peritubular angiotensin II was prevented by the presence of losartan (10(-6) M). By contrast, PD-23319, an AT(2)-receptor antagonist, did not alter the inhibitory effect of 10(-8) M angiotensin II. Finally, no additive effect of luminal and peritubular angiotensin II was observed. We conclude that both luminal and peritubular angiotensin II inhibit NaCl absorption in the MTALH via AT(1) receptors. Because of intrarenal angiotensin II synthesis, angiotensin II concentration in medullary tubular and interstitial fluids may be similar in vivo to the concentration that displays an inhibitory effect on NaCl reabsorption under the present experimental conditions.

Absorption↗
PubMed2003

Differentiated thick ascending limb (TAL) cultured cells derived from SV40 transgenic mice express functional apical NHE2 isoform: effect of nitric oxide.

Studying the apical Na/H exchanger NHE2 is difficult in the intact thick ascending limb (TAL) because of its weak expression and transport activity compared with the co-expressed NHE3. From a mouse transgenic for a recombinant plasmid adeno-SV(40) (PK4), we developed an immortalized TAL cell line, referred to as MKTAL, which selectively expresses NHE2 protein and activity. The immortalized cells retain the main properties of TAL cells. They have a stable homogeneous epithelial-like phenotype, express SV(40) T antigen and exhibit polarity with an apical domain bearing few microvilli and separated from lateral domains by typical epithelial-type junctional complexes expressing ZO1 protein. Tamm-Horsfall protein is present on the apical membrane. MKTAL cells express NHE2 and NHE1 proteins but not NHE3 and NHE4, whereby NHE2 protein is expressed selectively in the apical domain of the plasma membrane. NHE2 contributed about half of the total Na/H exchange activity. mRNAs for the Na-K-2Cl cotransporter-2 (NKCC2) and the anion exchangers AE2 and AE3 were also present. While acute exposure to NO donors did not alter NHE2 activity, chronic exposure inhibited NHE2 activity selectively and down-regulated NHE2 mRNA abundance. In conclusion, MKTAL cells retain structural and functional properties of their in vivo TAL counterparts and express functional NHE2 protein in the apical membrane, which may be inhibited by NO. Thus, MKTAL cells may be an appropriate model for studying the cellular mechanisms of NHE2 regulation.

Animals↗
PubMed2003

Urinary measurement of Na+/H+ exchanger isoform 3 (NHE3) protein as new marker of tubule injury in critically ill patients with ARF.

BACKGROUND: It has been shown that apical sodium transporters of the renal tubule can be detected by immunoblotting of urine membrane fraction from rats. We raised the hypothesis that protein levels of the Na+/H+ exchanger isoform 3 (NHE3), the most abundant apical sodium transporter in renal tubule, should be increased in urine of patients presenting with acute renal failure (ARF) with severe tubular cell damage and thus might be a noninvasive marker of acute tubular necrosis (ATN). METHODS: Sixty-eight patients admitted to the intensive care unit were studied prospectively (54 patients with ARF, 14 controls without renal dysfunction). Patients with ARF were divided into 3 subgroups as follows: prerenal azotemia, ATN, and intrinsic ARF other than ATN. Urinary NHE3 protein abundance was estimated from semiquantitative immunoblots of urine membrane fraction samples collected from patients. The amount of urinary NHE3 was compared with the fractional excretion of sodium (FeNa) and urinary retinol-binding protein (RBP). RESULTS: NHE3 was not detected in urine from controls. Levels of urinary NHE3 normalized to urinary creatinine level were increased in patients with prerenal azotemia and 6 times as much in patients with ATN, without overlap (ATN, 0.78 +/- 0.36; prerenal azotemia, 0.12 +/- 0.08; P < 0.001). Conversely, urinary NHE3 protein was not detected in patients with intrinsic ARF other than ATN. Normalized NHE3 level correlated positively with serum creatinine level in patients with tubular injury (R2 = 0.305; P = 0.0003). Values for FeNa and normalized urinary RBP did not discriminate ATN from intrinsic ARF other than ATN and prerenal azotemia, respectively. CONCLUSION: In patients with ARF, urinary NHE3 abundance might be a novel noninvasive marker of renal tubule damage, helping to differentiate prerenal azotemia, ATN, and intrinsic ARF other than ATN.

APACHE↗
PubMed2003

What keeps serum calcium levels stable?

Many body functions require that serum calcium levels remain stable over time. This stability is provided by cooperation among three organs: two effectors, the bone and the kidney, which control calcium movements into and out of the extracellular compartment, and the parathyroid glands, which produce and release parathyroid hormone (PTH). PTH acts on the bone and renal tubule. Provided the amount released is appropriate, this keeps extracellular calcium levels stable.

Bone and Bones↗
PubMed2003

Normocalcemic primary hyperparathyroidism: evidence for a generalized target-tissue resistance to parathyroid hormone.

Primary hyperparathyroidism (PHPT) is usually characterized by fasting hypercalcemia associated with inappropriately high PTH concentration. Nevertheless, cases of proven PHPT have been reported in normocalcemic patients. The purpose of the study was to investigate the mechanism(s) of persistent normocalcemia in PHPT. One hundred seventy-eight patients with PHPT were studied after exclusion of any evident cause of masked hypercalcemia. Patients were separated into normocalcemic (n = 34) and hypercalcemic (n = 144) subgroups on the basis of their fasting serum ionized calcium value. Patients with normocalcemic PHPT had, on average, a milder excess in PTH secretion assessed by a lower serum PTH concentration. Because of a clear overlap in PTH values between the two groups, normocalcemic and hypercalcemic patients were matched on the basis of serum PTH concentration, age, and sex. Patients with normocalcemic PHPT had lower fasting urine calcium excretion and renal tubular calcium reabsorption. In addition, normocalcemic patients differed from hypercalcemic patients by lower values of markers of bone turnover and plasma 1,25 dihydroxyvitamin D and higher values of renal phosphate threshold. In conclusion, a significant proportion of patients with PHPT are truly normocalcemic, and in addition to a milder increase in PTH secretion, the normocalcemic patients appear to display resistance to PTH action on bone and kidney.

Adult↗