Search PubMed⌕ Search

Biomedical subjects

G Friedlander

Publications and source records attributed to G Friedlander.

At least 37 records · Page 2Linked to original sources
PubMed1999

Halothane stimulates a Na+H+ antiporter involved in the regulation of intracellular pH in alveolar epithelial cells.

UNLABELLED: Changes in intracellular pH (pHi) of alveolar type II (ATII) cells have been involved in the pathophysiology of pulmonary edema. ATII cells have evolved several ions transporters to regulate their pHi, including a Na+H+ antiporter. Because halothane alters the activity of ion transporters in various cells types, it may also affect the activity of this Na+H+ antiporter. This study was performed 1) to characterize a Na+H+ antiporter in a model of ATII cells and 2) to investigate the effect of halothane on the activity of this antiporter. ATII cells were obtained from primary rat ATII cells transfected with a mutant of simian virus SV40 large T antigen (SV40-T2), and their pHi was monitored using the pH-sensitive fluorescent probe 2'-7' (bis carboxyethyl)-5(6')-carboxyfluorescein. We demonstrated in vitro that 1) a Na+H+ antiporter (apparent Km 6.8 +/- 3.4 mM, Vmax 0.0105 +/- 0.0013 delta UpHi/s) regulates the pHi of SV40-T2 cells and 2) at clinically relevant concentrations (10(-3) to 10(-5) M) and for a short exposure duration (60 min), halothane enhances the activity of this antiporter. Because ATII cell acidification has been associated with alterations in the alveolar epithelial barrier, halothane-induced intracellular alkalinization might exhibit some protective effect in clinical situations, such as aspiration pneumonia. IMPLICATIONS: In vitro, halothane induces an intracellular alkalinization of pneumocytes II via the activation of a Na+H+ antiporter. Because acidification of these cells has been associated with alterations in the alveolar epithelial barrier, halothane might exhibit some protective effect in clinical situations, such as aspiration pneumonia.

Anesthetics, Inhalation↗
PubMed1999

NaPO(4) cotransport type III (PiT1) expression in human embryonic kidney cells and regulation by PTH.

The aim of the present study was to characterize the type(s) of NaPO(4) cotransporter expressed in the human renal cell line HEK-293 and its regulation by parathyroid hormone (PTH) in wild-type cells and in cells transfected by the PTH/PTH-related protein (PTHrP) receptor. The results showed that human embryonic kidney HEK-293 cells expressed NaPO(4) cotransporter type III (PiT1) mRNA and protein. In contrast, type I (NPT1) or II (NPT2) cotransporter mRNA were not expressed. Na(+)-dependent phosphate uptake followed a Michaelis-Menten model (apparent maximal transport rate and affinity constant: 23.32 +/- 0.69 nmol PO(4). mg protein(-1). 10 min(-1) and 0.147 +/- 0.014 mM KH(2)PO(4), respectively), was stimulated by phosphate deprivation (maximal increase 24.5 +/- 0.8%, P < 0.001, after 15 h of phosphate deprivation), and was inhibited by increasing pH (3.6 +/- 0.2-fold decrease at pH 8.5, P < 0.0001). It was inhibited in a time- and concentration-dependent fashion by PTH in HEK-293 cells stably transfected by PTH/PTHrP receptors but not in parental HEK-293 cells. Maximal inhibition of Na(+)-dependent phosphate transport was observed at 30 min after the addition of 72 nM PTH-(1-34) (31.5 +/- 2.4% inhibition, P < 0.01). PTH inhibition of phosphate transport was maintained in phosphate-deprived cells and reversed by both GF109203X (10(-6) M) or staurosporine (5.5 nM), two protein kinase C inhibitors. Na(+)-dependent phosphate uptake was also significantly inhibited by phorbol 12-myristate 13-acetate (20.9 +/- 3.9% inhibition, P < 0.001) but not by dibutyril-cAMP (10(-4) M) or forskolin (50 microM). The physiological role played by type III NaPO(4) cotransport expression in the overall renal regulation of phosphate homeostasis remains to be established.

Biological Transport↗
PubMed1998

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors increase fibrinolytic activity in rat aortic endothelial cells. Role of geranylgeranylation and Rho proteins.

3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors (HRIs) have been recently shown to prevent atherosclerosis progression. Clinical benefit results from combined actions on various components of the atherosclerotic lesion. This study was designed to identify the effects of HRI on one of these components, the endothelial fibrinolytic system. Aortas isolated from rats treated for 2 days with lovastatin (4 mg/kg body wt per day) showed a 3-fold increase in tissue plasminogen activator (tPA) activity. In a rat aortic endothelial cell line (SVARECs) and in human nontransformed endothelial cells (HUVECs), HRI induced an increase in tPA activity and antigen in a time- and concentration-dependent manner. In SVARECs, the maximal response was observed when cells were incubated for 48 hours with 50 micromol/L HRI. An increase of tPA mRNA was also in evidence. In contrast, HRI inhibited plasminogen activator inhibitor-1 activity and mRNA. The effects of HRI were reversed by mevalonate and geranylgeranyl pyrophosphate, but not by LDL cholesterol and farnesyl pyrophosphate, and were not induced by alpha-hydroxyfarnesyl phosphonic acid, an inhibitor of protein farnesyl transferase. C3 exoenzyme, an inhibitor of the geranylgeranylated-activated Rho protein, reproduced the effect of lovastatin on tPA and plasminogen activator inhibitor-1 activity and blocked its reversal by geranylgeranyl pyrophosphate. The effect of HRI was associated with a disruption of cellular actin filaments without modification of microtubules. A disrupter of actin filaments, cytochalasin D, induced the same effect as lovastatin on tPA, whereas a disrupter of microtubules, nocodazole, did not. In conclusion, HRI can modify the fibrinolytic potential of endothelial cells, likely via inhibition of geranylgeranylated Rho protein and disruption of the actin filaments. The resulting increase of fibrinolytic activity of endothelial cells may contribute to the beneficial effects of HRI in the progression of atherosclerosis.

Animals↗
PubMed1998

[Regulation of phosphatemia and hypophosphatemia].

Phosphate is an essential element for cellular metabolism and bone mineralization. The kidney regulates phosphate homeostasis by modulating the proximal reabsorption of phosphate. This regulation is mediated by hormonal or autocrine/paracrine factors. Recent results concerning the molecular structure of phosphate transport systems have clarified the mechanisms underlying the effects of these mediators. Hypophosphatemia is a frequent biological finding which results either from an intracellular shift of phosphate, or from a defect in the intestinal absorption or a renal leak. The decrease in phosphate leads to a depletion in cellular ATP (which accounts for neurological and muscular symptoms), to bone demineralization and to renal lithiasis when a renal leak exists.

Absorption↗
PubMed1998

Halothane decreases Na,K-ATPase, and Na channel activity in alveolar type II cells.

BACKGROUND: Halothane alters surfactant biosynthesis and metabolism of alveolar type II cells. In addition to synthesizing surfactant, alveolar type II cells actively transport sodium (Na) from the alveolar space to the interstitium. Na enters the cells through amiloride-sensitive Na channels or Na cotransporters and is extruded by a Na pump. The purpose of this study was to examine the effects of halothane on Na transport activities. METHODS: Epithelial type II cells from adult rat lungs were exposed to halothane concentrations of 1, 2, and 4% from 0.5-4 h. In some experiments, cells that were exposed to 1% halothane for 1 h were allowed to recover after replacement of the medium for 15 and 30 min. Na transport was then evaluated by direct measurement of radiolabeled ions uptake. In addition, the effects of halothane were assessed in the absence of extracellular calcium (Ca) with or without 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an intracellular Ca chelating agent. RESULTS: Exposure of epithelial type II cells to halothane reduced the activity of sodium, potassium-adenosine triphosphatase, and amiloride-sensitive Na channels, whereas Na cotransporters were unchanged. The decrease in sodium, potassium-adenosine triphosphatase activity was maximal for 30 min of exposure and reached 50, 42, and 56% for halothane concentrations of 1, 2, and 4%, respectively, and did not change for longer exposure times. This effect was not prevented by either the absence of extracellular Ca or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid pretreatment. Exposure for 45 min to 1% halothane also decreased Na channel activity by 46%. These effects were completely reversible after 30 min of recovery. CONCLUSIONS: Sodium, potassium-adenosine triphosphatase, and amiloride-sensitive Na channel activities are impaired by halothane in alveolar type II cells in vitro. This inhibition could reduce transepithelial Na transport.

Alanine↗
PubMed1998

Dipyridamole decreases renal phosphate leak and augments serum phosphorus in patients with low renal phosphate threshold.

It has been shown that an acute infusion of dipyridamole increased renal phosphate reabsorption in rats and humans. A prospective study was performed to determine whether chronic treatment by dipyridamole given orally could decrease renal phosphate leak and increase serum phosphorus in patients with idiopathic low renal phosphate threshold (TmPO4/GFR < 0.77 mM). Sixty-four patients with low TmPO4/GFR were included and treated with dipyridamole (75 mg, 4 times daily) for more than 12 mo. Serum phosphorus, TmPO4/GFR, parathyroid hormone, serum calcium, and 1,25-dihydroxyvitamin D were measured sequentially before treatment, and after 3, 6 to 9, and 12 mo of treatment. Under chronic treatment with dipyridamole, TmPO4/GFR and serum phosphorus significantly increased in 80% of patients within 3 mo, with maximal values reached within 9 mo. This improvement persisted after 12 mo of treatment. In 28 patients, 1,25-dihydroxyvitamin D concentrations were above the normal range (> 42 pg/ml) and normalized in parallel with the increase of serum phosphorus. The 24-h calcium excretion (which was initially increased in patients with high vitamin D concentrations) and urolithiasis decreased under treatment. Ionized serum calcium and parathyroid hormone remained unchanged. After 2 yr, treatment was discontinued in three patients; serum phosphorus and TmPO4/GFR decreased within 1 mo after discontinuation. Dipyridamole at a dose of 75 mg 4 times daily increases low TmPO4/GFR and improves hypophosphatemia in patients with renal phosphate losses and can be used to treat these patients.

Administration, Oral↗
PubMed1998

Lovastatin modulates in vivo and in vitro the plasminogen activator/plasmin system of rat proximal tubular cells: role of geranylgeranylation and Rho proteins.

Interstitial fibrosis is one of the most deleterious events during the progression of renal deterioration after renal mass reduction. In vivo, hydroxymethylglutaryl CoA reductase inhibitors (HRI) were shown to reduce progression of glomerulosclerosis, but the mechanisms are still unclear. The present study investigates, in vivo, whether lovastatin, a potent HRI, was able to modulate the plasminogen-plasmin pathway, one of the most efficient systems involved in extracellular matrix remodeling, and characterizes in vitro the cellular mechanisms of these effects. Proximal tubules freshly isolated from rats treated for 2 d with lovastatin (4 mg/kg per d) showed increased tissue-type plasminogen activator (tPA) and urokinase (uPA) activities and antigens. Incubation with lovastatin (5 microM) of proximal tubules isolated from untreated rats induced an increase in tPA and uPA and a decrease in plasminogen activator inhibitor-1 (PAI-1) activities. In vitro, supernatants, cytosols, and membranes of renal proximal tubular cells in primary cultures had no detectable uPA activity, and lovastatin (0.1 to 10 microM) induced an increase in tPA and a decrease in PAI-1 activities and antigens. These effects were reversed by mevalonate and geranylgeranyl-pyrophosphate (GGPP) but not by farnesyl-pyrophosphate or LDL cholesterol. C3 exoenzyme, an inhibitor of the geranylgeranylated-activated Rho protein, reproduced the effect of lovastatin on tPA and PAI- activity and blocked its reversion by GGPP. The effect of lovastatin was associated with a disruption of cellular actin stress fibers, which was reversed by GGPP and reproduced by C3 exoenzyme. In conclusion, HRI can modify the fibrinolytic potential of proximal tubules, most likely via inhibition of geranylgeranylated Rho protein and disruption of the cytoskeleton. The resulting increase of proteolytic activity of tubular cells may serve to prevent extracellular matrix deposition and renal interstitial fibrosis.

Animals↗
PubMed1998

Ion transports in the middle ear epithelium.

Ion transports in the middle ear epithelium have been recently characterized. Experimental data using cell culture have found the existence of a sodium transepithelial transport that drives a water flow. This is thought to play a key role in the maintain of air-filled and fluid-free cavities. Impairment of this process is involved in the pathogenesis of secretory otitis media, which is the main cause of acquired hearing loss. Several modulations of this transport have been evidenced: (i) reactive oxygen species induced an endogenous synthesis of prostaglandin E2 (PGE2), which in turn increased the cAMP level and modulated ion transport rate; (ii) steroids increased the expression of the alpha subunit sodium channel mRNA, which changes paralleled the modulation of ion transport in the middle ear epithelium; (iii) moderate hypoxia selectively and reversibly decreased the rate of sodium transport, as a result of a parallel decrease in alpha epithelial sodium channel subunit mRNA level. These modulations may explain the course of middle ear pathology. However, the development of an in vivo model has become mandatory to assess the relevance of these data in the pathophysiology of the middle ear.

Adrenal Cortex Hormones↗
PubMed1997

Impaired flow-induced dilation in mesenteric resistance arteries from mice lacking vimentin.

The intermediate filament vimentin might play a key role in vascular resistance to mechanical stress. We investigated the responses to pressure (tensile stress) and flow (shear stress) of mesenteric resistance arteries perfused in vitro from vimentin knockout mice. Arteries were isolated from homozygous (Vim-/-, n = 14) or heterozygous vimentin-null mice (Vim+/-, n = 5) and from wild-type littermates (Vim+/+, n = 9). Passive arterial diameter (175+/-15 micron in Vim+/+ at 100 mmHg) and myogenic tone were not affected by the absence of vimentin. Flow-induced (0-150 microl/min) dilation (e. g., 19+/-3 micron dilation at 150 mmHg in Vim+/+) was significantly attenuated in Vim-/- mice (13+/-2 micron dilation, P < 0.01). Acute blockade of nitric oxide synthesis (NG-nitro- L-arginine, 10 microM) significantly decreased flow-induced dilation in both groups, whereas acute blockade of prostaglandin synthesis (indomethacin, 10 microM) had no significant effect. Mean blood pressure, in vivo mesenteric blood flow and diameter, and mesenteric artery media thickness or media to lumen ratio were not affected by the absence of vimentin. Thus, the absence of vimentin decreased selectively the response of resistance arteries to flow, suggesting a role for vimentin in the mechanotransduction of shear stress.

Animals↗
PubMed1997

Abnormal sulfate metabolism in vitamin D-deficient rats.

To explore the possibility that vitamin D status regulates sulfate homeostasis, plasma sulfate levels, renal sulfate excretion, and the expression of the renal Na-SO4 cotransporter were evaluated in vitamin D-deficient (D-D-) rats and in D-D- rats rendered normocalcemic by either vitamin D or calcium/lactose supplementation. D-D- rats had significantly lower plasma sulfate levels than control animals (0.93+/-0.01 and 1.15+/-0.05 mM, respectively, P < 0.05), and fractional sulfate renal excretion was approximately threefold higher comparing D-D- and control rats. A decrease in renal cortical brush border membrane Na-SO4 cotransport activity, associated with a parallel decrease in both renal Na-SO4 cotransport protein and mRNA content (78+/-3 and 73+/-3% decreases, respectively, compared with control values), was also observed in D-D- rats. Vitamin D supplementation resulted in a return to normal of plasma sulfate, fractional sulfate excretion, and both renal Na-SO4 cotransport mRNA and protein. In contrast, renal sulfate excretion and renal Na-SO4 cotransport activity, protein abundance, and mRNA remained decreased in vitamin D-depleted rats fed a diet supplemented with lactose and calcium, despite that these rats were normocalcemic, and had significantly lower levels of parathyroid hormone and 25(OH)- and 1,25(OH)2-vitamin D levels than the vitamin D-supplemented groups. These results demonstrate that vitamin D modulates renal Na-SO4 sulfate cotransport and sulfate homeostasis. The ability of vitamin D status to regulate Na-SO4 cotransport appears to be a direct effect, and is not mediated by the effects of vitamin D on plasma calcium or parathyroid hormone levels. Because sulfate is required for synthesis of essential matrix components, abnormal sulfate metabolism in vitamin D-deficient animals may contribute to producing some of the abnormalities observed in rickets and osteomalacia.

Animals↗
PubMed1997

Reduction of renal mass is lethal in mice lacking vimentin. Role of endothelin-nitric oxide imbalance.

Modulation of vascular tone by chemical and mechanical stimuli is a crucial adaptive phenomenon which involves cytoskeleton elements. Disruption, by homologous recombination, of the gene encoding vimentin, a class III intermediate filament protein mainly expressed in vascular cells, was reported to result in apparently normal phenotype under physiological conditions. In this study, we evaluated whether the lack of vimentin affects vascular adaptation to pathological situations, such as reduction of renal mass, a pathological condition which usually results in immediate and sustained vasodilation of the renal vascular bed. Ablation of 3/4 of renal mass was constantly lethal within 72 h in mice lacking vimentin (Vim-/-), whereas no lethality was observed in wild-type littermates. Death in Vim-/- mice resulted from end-stage renal failure. Kidneys from Vim-/- mice synthesized more endothelin, but less nitric oxide (NO), than kidneys from normal animals. In vitro, renal resistance arteries from Vim-/- mice were selectively more sensitive to endothelin, less responsive to NO-dependent vasodilators, and exhibited an impaired flow (shear stress)- induced vasodilation, which is NO dependent, as compared with those from normal littermates. Finally, in vivo administration of bosentan, an endothelin receptor antagonist, totally prevented lethality in Vim-/- mice. These results suggest that vimentin plays a key role in the modulation of vascular tone, possibly via the tuning of endothelin-nitric oxide balance.

Acetylcholine↗
PubMed1997

Characterization of detergent-insoluble complexes containing the cellular prion protein and its scrapie isoform.

Cells infected with prions contain both prion protein isoforms cellular prion protein (PrPC) and scrapie prion protein (PrPSc). PrPSc is formed posttranslationally through the pathological refolding of PrPC. In scrapie-infected ScN2a cells, the metabolism of both PrP isoforms involves cholesterol-dependent pathways. We show here that both PrPC and PrPSc are attached to Triton X-100-insoluble, low-density complexes or "rafts." These complexes are sensitive to saponin and thus probably contain cholesterol. This finding suggests that the transformation PrPC --> PrPSc occurs within rafts. It also reveals the existence of rafts in late compartments of the endocytic pathway, where most PrPSc resides. When Triton X-100 lysates of cells were incubated at 37 degrees C prior to density analysis, PrPC was still found in buoyant complexes, although it now failed to sediment at high speed. This property was shared by another glycophosphatidyl inositol protein, Thy-1, and also by the raft resident GM1. In one ScN2a clone and in the brain of a Syrian hamster with scrapie, Triton X-100 extraction at 37 degrees C permitted resolution of PrPC and PrPSc into two distinct peaks of different densities. This suggests that there are two populations of PrP-containing rafts and may permit isolation of PrPC-specific rafts from those containing PrPSc. Our findings reinforce the contention that rafts are involved in various aspects of PrP metabolism and in the "life cycle" of prions.

Animals↗