Glucocorticosteroids increase sodium transport in middle ear epithelium

The effect of glucocorticosteroids on ion transport was investigated on a middle ear cell line with the short-circuit current (Isc) technique. Dexamethasone (DXM) produced a dose- and time-dependent increase in Isc. Concentration of half-maximal stimulation was 2.68 x 10(-8) M. This effect was blunted by the glucocorticoid antagonist RU-38486 and was related to Na+ transport, as evidenced by the inhibition induced by 1) apical addition of the Na+ channel inhibitor benzamil (10(-6) M) or 2) substitution of Na+ with N-methylglucamine in the incubation medium. The increase in Na+ transport resulted from a primary modulation of apical Na+ entry, since 1) the Na(+)-K(+)-ATPase activity of cellular homogenates was not modified by corticosteroids and 2) the DXM-induced increase in the ouabain-sensitive uptake of 86Rb was blunted by benzamil. Ribonuclease protection assay revealed 1) a constitutive expression of the mRNA encoding the alpha-subunit of the epithelial Na+ channel and 2) that DXM increased the expression of this transcript. This increase was dose dependent and paralleled changes in transepithelial Na+ transport. This study suggests that a component of the beneficial effect of steroid therapy for the treatment of otitis media might be related to increased fluid clearance.

Locally formed 5-hydroxytryptamine stimulates phosphate transport in cultured opossum kidney cells and in rat kidney

Renal proximal tubular cells have been shown to express aromatic L-amino acid decarboxylase (L-AAAD), which converts L-dopa into dopamine and 5-hydroxytryptophan [(OH)Trp] into 5-hydroxytryptamine (5-HT; serotonin). Because 5-HT receptors have been demonstrated in proximal cells, we hypothesized that 5-HT may act as an autocrine/paracrine modulator of proximal transport. We evaluated this possibility in opossum kidney (OK) cells, a renal epithelial cell line with a proximal phenotype expressing 5-HT1B receptors, and in intact anaesthetized rats. 5-HT synthesis by OK cells increased with incubation time and (OH)Trp concentration, and was abolished by benserazide, an L-AAAD inhibitor. 5-HT reversed parathyroid hormone (PTH)-induced cAMP accumulation in a pertussis toxin-sensitive manner and reduced the PTH inhibition of P(i) uptake without affecting the NaP(i)-4 mRNA level. The effects of 5-HT on cAMP generation and Na-P(i) co-transport were reproduced by (OH)Trp, except in the presence of benserazide, and by L-propranolol and dihydroergotamine, two 5-HT1B receptor agonists. In rats, (OH)Trp and dihydroergotamine decreased fractional P(i) excretion. Benserazide abolished the effect of (OH)Trp but not that of dihydroergotamine.

IN CONCLUSION

(i) locally generated 5-HT blunts the inhibitory effect of PTH on Na-P(i) co-transport in OK cells; (ii) endogenous 5-HT decreases P(i) excretion in rats; and (iii) 5-HT is a paracrine modulator involved in the physiological regulation of renal P(i) transport.

Expression of alternatively spliced isoforms of the parathyroid hormone (PTH)/PTH-related peptide receptor messenger RNA in human kidney and bone cells

Using a PCR-based strategy, two variants of the PTH/PTH-related peptide (PTH-rp) receptor mRNA were identified in human kidney, SaOS-2 human osteoblast cells, and rat bone that are produced by alternative splicing of exons coding for the N-terminal portion of the receptor. In the S-N3-E2 isoform, the exon coding the signal peptide (S) is spliced to an alternative 3'-acceptor site, producing a product respecting the reading frame, but in which the E1 exon is replaced by 12 amino acids derived from the N3 intron. In the S-E2 isoform, in which the E1 exon is deleted by cassette exclusion, the reading frame is changed, but a truncated receptor may be produced by reinitiation of translation at an overlapping stop/start codon. After transfection of COS and Chinese hamster ovary cells with the originally described S-E1-E2 isoform and the two splice variants, active transcription of PTH/PTH-rp receptor mRNA was detected by RT-PCR in all cases. Cell lines transfected with the S-E1-E2 and S-N3-E2 isoforms displayed a 15- to 25-fold and 2- to 3-fold increase, respectively, in cAMP content after stimulation with 2.4 x 10(-7) M human PTH(1-34), whereas cells transfected with the S-E2 isoform did not respond. PTH elicited an increase in intracellular calcium only in cells transfected with the S-E1-E2 isoform. Studies evaluating the surface expression of receptors using anti-human PTH/PTH-rp receptor antibodies and the ability of transfected cells to bind [125I]PTH-rp indicated that the low or absent responses to PTH stimulation resulted, at least in part, from low surface expression of the S-N3-E2 and S-E2 isoforms. These studies support the conclusion that exon E1 is extremely important in promoting surface expression of the PTH/PTH-rp receptor but indicate that isoforms lacking this exon can retain the ability to recognize PTH. The possible intracellular expression of these splice variants, which account for 15-20% of total PTH/PTH-rp receptor mRNA, needs to be evaluated.

Regulation of renal phosphate handling: recent findings

Our knowledge of renal phosphate handling and its regulation has expanded in the past 2 years because of the molecular identification of sodium-phosphate cotransport systems. New tools (molecular probes and antibodies) have allowed dissection out of some of the molecular and cellular mechanisms underlying the adaptation of phosphate transport to dietary content, the phosphaturic effect of parathyroid hormone or glucocorticoids and the renal phosphate leak in hypophosphataemic rickets.

Inhibition of Na-K-ATPase activity after prolonged hypoxia in an alveolar epithelial cell line

Exposure to alveolar hypoxia may induce acute pulmonary edema. Because the vectorial sodium transport by alveolar epithelium represents an important mechanism for alveolar edema clearance, we examined whether hypoxia affects Na-K-ATPase activity in cultured SV40-transformed rat alveolar type II cells (SV40 ATII cells). Hypoxic exposures (O or 5% O2 for at least 12 h) induced a time- and O2 concentration-dependent decrease in ouabain-sensitive rubidium (osRb) influx. Neither the sensitivity of Rb influx to ouabain nor the maximum velocity of the enzyme measured on crude cell homogenates was affected by hypoxia. The osRb influx decrease was independent of hypoxia-induced ATP depletion. Na-K-ATPase inhibition was most likely related to impaired calcium homeostasis, because 1) calcium influx was increased in hypoxic cells, 2) hypoxia-induced osRb influx decrease was completely prevented by nifedipine (10-5 M), and 3) osRb influx decreased in normoxic cells incubated with ionomycin (10-6 M, 15 min). Furthermore, hypoxia-induced Na-K-ATPase impairment might be due, at least in part, to the endogenous release by hypoxic cells of a lipidic factor in extracellular medium, because incubation of normoxic cells with hypoxic cells conditioned medium (CM), or with the lipidic subphase from hypoxic cells CM, also induced a partial decrease in osRb influx. This decrease was associated with increased calcium influx into normoxic cells and was suppressed either by the removal of external calcium or by nifedipine, suggesting that the lipidic factor exerted its inhibitory action on Na-K-ATPase via an enhancement of calcium entry. These results indicate that prolonged hypoxic exposure impairs Na-K-ATPase activity in SV40 ATII cells and may therefore decrease the vectorial sodium transport by alveolar epithelium.

Inhibition of ecto-5'-nucleotidase by nitric oxide donors. Implications in renal epithelial cells

We evaluated, in renal epithelial cells with a proximal tubule phenotype, the effect of nitric oxide (NO) on ecto-5 -nucleotidase (5'-N U), the underlying mechanism and its functional consequence. Sodium nitroprusside (SNP, 1-1000 microM), a NO donor, inhibited 5'-NU activity in a time- and concentration-dependent manner. Consequently, NO blunted the inhibition by extracellular cyclic AMP (cAMP, 10-1000 microM) of sodium-phosphate cotransport, a pathway which involves degradation of adenosine monophosphate (AMP) by 5'-NU. SNP-induced inhibition of 5'-NU was not mediated by cyclic GMP, since it was not mimicked by atrial natriuretic peptide, and was reproduced by isosorbide dinitrate and sodium nitrate, two NO donors. SNP and genuine NO decreased the activity of 5'-NU in renal homogenates, and the effect of SNP was potentiated by dithiothreitol and glutathione, but not by nicotinamide adenine dinucleotide. In vivo in rats, kidney ischemia/reperfusion, which activates inducible NO-synthase, inhibited renal 5'-NU. This inhibition was prevented by Nomega-nitro-L-arginine methyl ester, a NO-synthase inhibitor. These results indicate that: (i) NO-related activity inhibited the activity of an ecto-enzyme, 5'-NU, most likely through S-nitrosylation of the enzyme; (ii) inhibition of 5'-NU activity by NOx, which can occur in vivo under pathophysiological conditions, affected the extent to which extracellular cAMP inhibited sodium-Pi cotransport.

[Regulation and physiopathology of phosphate transport]

Renal phosphate transport is subjected to a fine tuning which involves hormones and local mediators and results in adaptation of excretion to dietary contents. Recent insights into the molecular structure of phosphate transporters have shed light on the mechanisms which underline the effects of these mediators. Another important repercussion of these advances is the identification of pathological states such as renal phosphate leaks and the elaboration of diagnostic and therapeutic strategies aiming to improve these troubles.

Locally formed dopamine modulates renal Na-Pi co-transport through DA1 and DA2 receptors

The involvement of dopamine (DA) receptor subtypes in regulation of renal phosphate transport by DA, either exogenous or locally synthesized from L-dihydroxyphenylalanine (L-dopa) was evaluated in opossum kidney (OK) cells with proximal tubular phenotype. DA synthesis from L-dopa by OK cells was abolished by carbidopa and benserazide, two dissimilar inhibitors of aromatic L-amino acid decarboxylase. L-Dopa stimulated cyclic AMP generation and inhibited Na-dependent Pi uptake, and these effects were abolished by carbidopa and benserazide. The effects of L-dopa or DA on cyclic AMP generation and on Na-Pi co-transport were mimicked by SKF 38393, a DA1 receptor agonist, and were potentiated by S-sulpiride, a DA2 receptor antagonist. Bromocriptine, a DA2 receptor agonist, blunted in a pertussis toxin-dependent manner parathyroid hormone (PTH)-induced cyclic AMP generation and inhibition of Pi uptake. In contrast with PTH, neither L-dopa nor DA affected significantly the cytosolic calcium concentration. These results support the involvement of DA1 and DA2 receptors, positively and negatively coupled into adenylate cyclase respectively, in modulation of renal phosphate transport.

Insulin-like growth factor I, a unique calcium-dependent stimulator of 1,25-dihydroxyvitamin D3 production. Studies in cultured mouse kidney cells

Previous in vivo and in vitro studies suggest that insulin-like growth factor (IGF-I) could be a regulator of the renal production of 1,25-(OH)2D3. In the present work, the local effect of low nanomolar concentrations of IGF-I on the 25-OH-D3-1 alpha-hydroxylase activity and the mechanism of its action have been investigated. To do so, an in vitro model of mouse proximal tubular cells in primary culture has been developed. These cells bear specific high affinity IGF-I binding sites (apparent Kd = 1.95 +/- 0.46 nM) and express the ability to convert [3H]25-(OH)D3 into [3H]1,25-(OH)2D3 (Km = 139 +/- 15.7 nM). Human recombinant IGF-I (10-100 ng/ml) stimulated both sodium-dependent phosphate uptake and 1,25-(OH)2D3 synthesis by these cells, in a time- and dose-dependent manner. IGF-I did not alter the apparent Michaelis constant but increased the maximum velocity of the 25-OH-D3-1 alpha-hydroxylase activity. This effect required protein synthesis. It was not affected by calphostin or GF109203X, two protein kinase C inhibitors, and was not mimicked by phorbol 12-myristate 13-acetate. In contrast, it was blocked by verapamil, a calcium channel blocker. Calcium depletion of the medium blunted the IGF-I effect but not that of human 1-34 parathyroid hormone 5 x 10(-8) M. IGF-I thus appears to be the first example of a physiological calcium-dependent regulator of the renal metabolism of vitamin D.

Lipopolysaccharides stimulate Na-dependent transport in alveolar cells and protect against oxidant injury

We have evaluated the effect of lipopolysaccharides (LPS), endotoxins from gram negative bacteria, on sodium-coupled amino acid and phosphate transport by alveolar epithelial type II cells and on their alteration induced by oxidants. Alveolar type II cells were obtained by enzymatic digestion of rat lung and grown for 24 h prior to incubation with LPS and then exposed or not exposed to H2O2 (2.5 mM; 20 min). LPS (10 micrograms/ml, 24 h) induced a significant increase in the Na-dependent component of alanine and phosphate uptake while they decreased Na,K-ATPase activity measured by ouabain-sensitive 86Rb influx. We showed that this stimulatory effect i) was independent from macrophage products since it was not mimicked either by supernatant of LPS-treated alveolar macrophages or by pretreatment with tumor necrosis factor and/or interleukin 1 and ii) was dependent on protein synthesis since it was abolished by protein synthesis inhibitors cycloheximide and actinomycin D. Moreover, LPS blunted H2O2-induced decrease of Na-dependent alanine and phosphate uptake. This protective effect of LPS against H2O2 injury i) was independent of macrophage products, ii) was abolished by cycloheximide, and iii) was not associated with either changes in extracellular H2O2 clearance or catalase and glutathione peroxidase activities. We conclude that, in alveolar type II cells, LPS stimulate sodium-coupled transport by a process involving protein synthesis and partially prevent H2O2-induced decrease of Na-coupled transport without discernible change in antioxidant activities.

Role of adenosine on glucagon-induced cAMP in a human cortical collecting duct cell line

The hormonal responsiveness profile of the cortical collecting duct varies from one species to another. To identify the hormones and agonists that modulate the functions of this tubule segment in the human species, we generated a cell line (HCD) immortalized by SV40 virus. The tubular origin of this cell line was assessed by the expression of collecting duct-specific antigens and the ability of vasopressin to increase by nine-fold cAMP synthesis. Glucagon and adenosine stimulated cAMP synthesis, and atrial natriuretic peptide stimulated cGMP synthesis in a concentration-dependent manner. Bradykinin, adenosine and angiotensin increased intracellular calcium concentration ([Ca2+]i). Because adenosine can regulate tubular functions, we examined its role on glucagon-induced cAMP synthesis. Using adenosine analogs, we demonstrated that HCT cells both expressed adenosine type-2 (A2) receptors which stimulated cAMP production, and adenosine type-1 (A1) receptors linked to [Ca2+]i increase which inhibited glucagon-stimulated cAMP synthesis. The inhibitory effect was abolished by pertussis toxin, and was neither due to [Ca2+]i increase nor to protein kinase C activation, which indicated that some A1 adenosine receptors were directly negatively coupled to adenylyl cyclase. These results suggest that adenosine can modify human cortical collecting duct functions in opposite ways according to the adenosine receptor activated.

Oxygen metabolites modulate sodium transport in gerbil middle ear epithelium: involvement of PGE2

The middle ear epithelium and respiratory epithelia share basic properties such as homeostasis of air-filled cavities and mucociliary clearance toward the pharynx. With the middle ear SV40-transformed (MESV) cell line, we used the short-circuit current (Isc) technique to investigate changes in ion transport induced by oxidants. Xanthine and xanthine oxidase on the basal side of the monolayers dramatically increased Isc up to 50%. This effect was not affected by superoxide dismutase or mannitol, but could be blunted by catalase or 1,3-dimethyl-2-thiourea. Increasing concentrations of H2O2 from 10(-5) to 5 x 10(-4) M produced a dose-dependent increase in Isc from 0.26 +/- 0.16 up to 4.21 +/- 0.43 microA/cm2 (P < 0.05, n = 5). Concentration of half-maximal stimulation (EC50) was 4.68 x 10(-5) M. This effect was inhibited by indomethacin and was related to a sodium transport, since the H2O2-induced increase in Isc could be prevented or abolished by 1) apical addition of benzamil (10(-6)M) and 2) substitution of sodium with N-methyl-glucamine. H2O2 exposure also induced indomethacin-sensitive increase in released prostaglandin (PG) E2 (EC50 = 5.62 x 10(-5) M) and in cAMP content (EC50 = 3.95 x 10(-5) M) with similar kinetics. These results suggest that exposure of MESV cells to oxidants stimulates the production of PGE2, which in turn increases the transepithelial sodium transport rate.

Parathyroid hormone stimulates ecto-5'-nucleotidase activity in renal epithelial cells: role of protein kinase-C

PTH-induced phosphaturia is exerted in part by cAMP added to the renal tubular lumen under the influence of the hormone. Modulation of renal phosphate transport by luminal cAMP requires degradation of the nucleotide into adenosine by brush-border membrane ectoenzymes, among them ecto-5'-nucleotidase (5'-NU). Hormonal modulation of 5'-NU activity was evaluated in cultured opossum kidney cells. PTH (1-100 nM) stimulated 5'-NU in a time-, concentration-, and protein synthesis-dependent manner. The effect of PTH-(1-34) was mimicked by PTH-(3-34), which does not activates adenylate cyclase, and by phorbol 12-myristate 13-acetate (PMA), but not by forskolin or (Bu)2cAMP. Down-regulation or pharmacological inhibition of protein kinase-C (PKC) abolished the effect of PTH fragments and PMA. PTH fragments increased intracellular Ca2+ and translocated PKC activity to the membrane. PTH or PMA did not affect 5'-NU messenger RNA content. Inhibition of sodium-phosphate cotransport by extracellular cAMP was decreased by 5'-NU inhibition and was magnified by PTH. These results indicate that 1) PTH stimulates 5'-NU activity in renal proximal tubular cells in a manner involving PKC activation and de novo protein synthesis; and 2) this effect participates in PTH modulation of renal phosphate transport.

Adult-onset idiopathic phosphate diabetes. I. Chronic pseudoinflammatory back pain and osteopenia

STUDY OBJECTIVE

to investigate clinical, laboratory test, and bone mineral density abnormalities in 19 adults with phosphate diabetes of unknown etiology diagnosed in a rheumatology department on the basis of a maximal rate for tubular reabsorption of phosphate (TmPO4/GFR) of 0.77 or less.

RESULTS

there were 14 males and five females with a mean age of 36.7 years (range 20 to 68 years) at symptom onset and 43.9 years (24-70) at diagnosis. Seventeen patients (90%) had back pain and 13 (68%) had nerve root pain. The pain was nocturnal only or both nocturnal and diurnal in 14 cases (74%). Other manifestations were fatigue (n = 7, 37%), myalgia (n = 6, 32%), fracture (n = 6, 32%), renal colic (n = 4, 21%), and pseudodepression (n = 10, 53%). Laboratory test abnormalities were as follows: serum phosphate, 0.72 mmol/L (0.58-0.89); rate for tubular reabsorption of phosphate, 74% (54-84%); maximal rate for tubular reabsorption of phosphate, 0.58 (0.4-0.76); urinary calcium/urinary creatinine > 0.48 in nine patients (47%); and fractional potassium excretion > 20% in seven patients (37%). Normal values were found for serum levels of Ca++, Na++, Mg++, creatinine, cortisol, T3, T4, TSH, 25(OH)D3, and 1,25(OH)2 D3. Tests for glycosuria and amino aciduria were negative. Bone mineral density measurements showed z-scores of -2.13 (+0.9 to -4.25) at L2-L4, and -1.34 (+1.5 to -3.2) at the femoral neck. Bone histology showed osteoporosis with a mild increase in osteoid deposition.

CONCLUSIONS

idiopathic adult-onset phosphate diabetes manifests as chronic back pain and nerve root pain, sometimes with fatigue and depression. Bone mineral density values are decreased and histology shows osteopenia. Differential diagnoses include spondyloarthropathy, disk disease, fibromyalgia, and depression. Determination of the maximal rate for tubular reabsorption of phosphate is the only means of establishing the diagnosis.

Local action of phosphate depletion and insulin-like growth factor 1 on in vitro production of 1,25-dihydroxyvitamin D by cultured mammalian kidney cells

The hormonal form of vitamin D, 1,25(OH)2D, is synthesized mostly in proximal renal tubular cells. Experimental and clinical studies suggest that the growth hormone may be involved in growth-related fluctuations of plasma 1,25(OH)2D and in the increase of 1,25(OH)2D induced by in vivo phosphate deprivation, an action possibly mediated by insulin-like growth factor 1 (IGF 1). We tested the effects of phosphate depletion and IGF 1 addition on 1,25(OH)2D3 production in cultured kidney cells: opossum kidney (OK) cells, LLC-PK 1, and rabbit's proximal tubular cells. Confluent cell monolayers were preincubated in various phosphate concentrations, in the presence and absence of IGF 1. Then, 5 nM of [3H]25 (OH)D3 or 2 microM of 25 (OH)D3 were added to the medium and the cells were incubated for a further 120 min. The amount of biosynthesized 1,25(OH)2D3 in lipid extracts was determined after two different straight phase high performance liquid chromatographies. The experiment showed the following: (a) LLC-PK 1 and rabbit's cells expressed a detectable ability to synthesize 1,25(OH)2D3, while OK cells did not. (b) Partial or total phosphate deprivation increased the amount of 1,25(OH)2D3 produced, respectively in LLC-PK 1 and in rabbit's cells. (c) IGF 1 (25 ng/ml) increased 1,25(OH)2D3 production in rabbit's cells, particularly in phosphate-free medium (1.6-fold), and in LLC-PK 1 cells, in partial phosphate depletion (2.75-fold in 1 mM phosphate, P = 0.015, n = 5, and 3.2-fold in 0.5 mM phosphate, P = 0.043, n = 4). Our findings demonstrate a local action of phosphate depletion and of IGF 1 on 1,25-dihydroxyvitamin D3 production.

Pathophysiology of middle ear epithelium: a new role for prostaglandin E2

INTRODUCTION

Otitis media with effusion is a disease of the middle ear epithelium resulting from a decreased sol layer as well as increased mucus secretion and plasma-derived protein transudation, which causes mucus plugging. Because the epithelium keeps the middle ear cavities fluid-free and air-filled, we investigated its fluid transport capacities, which may be involved in both efficacy of the mucociliary clearance and drying-out of the posterior ear cavities (Yen PT et al: Acta Otolaryngol (Stockh) 113, 1993). We have established the absorptive capacity of middle ear epithelial cells in primary culture (Herman P, et al: Am J Physiol 262, 1992). However, the paucity of cells obtained by enzymatic digestion led us to develop a new model for further investigation of middle ear epithelial cell.

METHODS

We established a middle ear cell line (MESV) using simian virus 40 (SV40) infection of middle ear epithelial cells from the Mongolian gerbil.

RESULTS

Investigation of the transport processes using the short-circuit current technique showed that MESV cells retain most characteristics of the original middle ear epithelial cells. Transepithelial sodium transport from the apical to the basal side was responsible for the transepithelial lumen-negative potential difference.

CONCLUSION

The presence of high concentrations of prostaglandin E2 in the middle ear effusions has been documented. This work investigates the effect of prostaglandin E2 on the rate of transepithelial ion transport of MESV cells. Prostaglandin E2 increased the rate of electrogenic sodium transport by means of increase in the intracellular cyclic adenosine monophosphate (cAMP) content. Such a modulation of sodium transport in the course of otitis media could be responsible for the reduced periciliary sol layer that impairs the mucociliary clearance.

Adenoviral-mediated gene transfer to renal tubular cells in vivo

The efficient introduction of genetic material into quiescent renal cells is potentially important in the study of renal physiopathology and for gene therapy of kidney related disorders. A replication-deficient adenoviral vector that contained a reporter gene encoding the nuclear beta-galactosidase was either selectively perfused into the renal artery or infused through a retrograde catheter into the pyelic cavity of the left kidney of adult rats. Highly efficient gene transfer was achieved by either route of administration, and nuclear beta-galactosidase activity was detected for two to four weeks following a progressive decline of expression. Genetically-modified cells were identified as proximal tubular cells when the adenoviral vector was selectively perfused via the renal artery, while tubular cells from the papilla and medulla were selectively transduced by retrograde infusion of the viral vector. No obvious cytopathic effect was observed. We conclude that: (i) efficient gene transfer in renal tubular cells can be achieved by adenoviral vectors; (ii) the targeted cell population can be chosen through the route of administration.

Glucocorticoid inhibition of Na-Pi cotransport in renal epithelial cells is mediated by protein kinase C

The effect and mechanism of action of glucocorticoids (GC) on Na-Pi cotransport were evaluated in opossum kidney cells. Dexamethasone (1-1000 nM) inhibited sodium-dependent Pi uptake in a time- and concentration-dependent manner. Inhibition was maximal after a 6-h incubation with dexamethasone and was prevented by cycloheximide and actinomycin D. The effect was related to a 37% decrease of the Vmax value after incubation with 100 nM dexamethasone. The effect of dexamethasone was mimicked by cortisol and blocked by GC receptor antagonists RU38486 and progesterone. GC affected neither glucose or alanine uptake nor Na/H exchange activity. Inhibition of Pi uptake persisted when Na/H was blocked by amiloride or dimethylamiloride. GC had no effect on basal or parathyroid hormone- and forskolin-stimulated intracellular cAMP content. Dexamethasone and extracellular cAMP, parathyroid hormone, or 3-isobutyl-1-methylxanthine had additive inhibitory effects on Pi uptake. Staurosporine, GF109203X, or calphostin C (three dissimilar inhibitors of protein kinase C (PKC)) and PKC down-regulation blunted the inhibitory effect of glucocorticoids on Pi uptake. GC increased both membrane-bound PKC activity and the membrane/cytosol PKC activity ratio. This is the first report of GC activation of PKC in renal cells, which appears to mediate the steroid inhibitory effect on Pi transport.

Successful renal autotransplantation in a patient with bilateral renal artery thrombosis

Bilateral renal artery thrombosis is a rare but traumatic injury that is most commonly caused by sudden deceleration. Traditional methods of repair (e.g., in situ repair, bypass graft, and thrombectomy) have poor success rates. This report is the first successful use of autotransplantation in a patient with bilateral renal artery thrombosis.