Renal transport of phosphate: role of alkaline phosphatase

1981 ◽  
Vol 59 (4) ◽  
pp. 311-323 ◽  
Author(s):  
Claude PetitClerc ◽  
Gérard E. Plante
Keyword(s):  
Alkaline Phosphatase ◽  
Renal Artery ◽  
Brush Border ◽  
Ionic Species ◽  
Kidney Cortex ◽  
Renal Transport ◽  
Tubular Transport

A new aspect in the study of mechanisms involved in the renal transport of phosphate, the role of alkaline phosphatase (ALP), was introduced by this laboratory in 1977. The present experiments were designed to examine the effects of levamisole, a known inhibitor of ALP, first on in vitro phosphotransferase activity of rat brush border ALP and second on in vivo transport of phosphate and other ionic species, using both clearance and micropuncture techniques.The results indicate that levamisole inhibits in vitro ALP of brush borders obtained from kidney cortex of dogs and rats by reducing the turnover of orthophosphate on the enzyme. When administered in vivo this drug inhibits the net reabsorption of phosphate in these two different mammalian species. Tubular reabsorption of phosphate falls from 87.0 ± 2.9 to 72.1 ± 3.5% when levamisole is administered in the dog femoral vein (25 mM) and from 85.1 ± 3.4 to 71.3 ± 3.2% when levamisole is infused in the dog renal artery (2.5 mM). In the intact rat this parameter falls from 96.7 ± 1.4 to 46.8 ± 9.8% during levamisole and it also decreases from 98.9 ± 0.8 to 67.4 ± 6.7% in the thyroparathyroidectomized animal. The effect of levamisole on the net tubular transport of phosphate is closely related (r = 0.967) to the amount of the drug reaching the tubular lumen from glomerular filtration: that fraction of administered levamisole which first reaches the early segments of the proximal tubule, where the bulk of filtered phosphate is normally reabsorbed.The effect of levamisole appears to be specific for phosphate as no change in the net transport of other ionic species could be documented in the dog experiments. Levamisole produces a significant decrement in renal plasma flow. The mechanism of this effect is not yet determined but certainly created a situation leading to underestimation of the levamisole effect on the net tubular transport of phosphate.Microinjections of 32P either diluted in isotonic saline or administered with flavone phosphate (0.2 mM), a substrate of ALP, were performed in early segments of superficial proximal tubules of the rat. Urinary 32 P recovery averaged 14 ± 4% and 34 ± 8% following saline and flavone phosphate, respectively.The effect of levamisole does not appear to be mediated by changes in parathyroid hormone secretion or other extrarenal humoral substances as a depression of phosphate reabsorption is seen when the drug is administered in the renal artery. The rapid and reversible effect of flavone phosphate suggests that this compound specifically interacts with ALP of brush border membranes.

Effect of experimentally induced hypothyroidism on sulfate renal transport in rats

1999 ◽  
Vol 276 (1) ◽  
pp. F164-F171 ◽  
Author(s):  
Kazuko Sagawa ◽  
Heini Murer ◽  
Marilyn E. Morris
Keyword(s):  
Sodium Sulfate ◽  
Basolateral Membrane ◽  
Kidney Cortex ◽  
Renal Transport ◽  
Sulfate Anion ◽  
Protein Levels ◽  
Serum Sulfate ◽  
Hypothyroid Patients

Decreased serum sulfate concentrations are observed in hypothyroid patients. However, the mechanism involved in thyroid hormone-induced alterations of renal sulfate homeostasis is unknown. The objectives of this investigation were to determine the effect of 6-propyl-2-thiouracil (PTU)-induced hypothyroidism in rats on 1) the in vivo serum concentrations, renal clearance, and renal reabsorption of sulfate, 2) the in vitro renal transport in brush-border membrane (BBM) and basolateral membrane (BLM) vesicles, and 3) the cellular mechanism of the hypothyroid-induced alteration in sulfate renal transport. Serum sulfate concentrations, renal fractional reabsorption of sulfate, and creatinine clearance were decreased significantly in the hypothyroid group. The V max values for sodium-sulfate cotransport in BBM were significantly decreased in the kidney cortex from the hypothyroid animals (0.90 ± 0.31 vs. 0.49 ± 0.08 nmol ⋅ mg−1 ⋅ 10 s−1, n = 5–6, P < 0.05) without changes in K m. There were no significant differences in V max and K m for sulfate/anion exchange transport in BLM. Sodium-dependent sulfate transporter (NaSi-1) mRNA and protein levels were significantly lower in the kidney cortex from hypothyroid rats. Hypothyroidism did not alter the membrane motional order (fluidity) in BBM and BLM, which indicates that the changes in the membrane fluidity do not represent the mechanism for the altered renal transport. These results demonstrate that PTU-induced hypothyroidism decreases sodium-sulfate cotransport by downregulation of the NaSi-1 gene.

Renal adaptation to phosphate deprivation in the Hyp mouse with X-linked hypophosphatemia

1979 ◽  
Vol 57 (6) ◽  
pp. 938-944 ◽  
Author(s):  
H. S. Tenenhouse ◽  
C. R. Scriver
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Control Diet ◽  
Fractional Excretion ◽  
Kidney Cortex ◽  
Phosphate Deprivation ◽  
Renal Adaptation ◽  
Pi Deprivation

The mechanism of renal adaptation to variation in dietary inorganic phosphate (Pi) was investigated in intact Hyp/+ (heterozygous) mice and +/+ (normal homozygous) female siblings. Hyp/+ mice were selected for expression of the X-linked Hyp allele, when fed the control diet (0.6% P), by evidence of persistent postweaning hypophosphatemia (1.78 ± 0.08 mM, mean ± SE, versus 2.68 ± 0.19 mM in +/+ siblings (p < 0.01)). Hyp/+ mice had an elevated fractional excretion index for Pi (FEIPi) (0.570 ± 0.024, mean ± SE) on this diet versus +/+ siblings (0.352 ± 0.025, p < 0.001). Renal cortex content of Pi (~46 nmol/mg protein) and net radioisotopic uptake of Pi by slices were similar in Hyp/+ and +/+ mice. Purified brush border membrane vesicles (BBMV) from Hyp/+ kidney cortex transported labelled Pi (100 μM) by a Na+-dependent mode at about one-half the rate (p < 0.001) observed in +/+ mice. Hyp/+ and +/+ mice fed a low P diet (0.03%) maintained their phenotypic differences in vivo and in vitro. Both adapted to chronic (> 2 week) Pi deprivation with a striking reduction (40- to 50-fold) of FEIPi (p < 0.001) and a fall in plasma [Pi] (p < 0.001). Neither the renal Pi content nor uptake of Pi by slices changed in deprived Hyp/+ and +/+ mice. On the other hand, BBMV uptake by Na+-dependent cotransport increased 200% (p < 0.001) during Pi deprivation in both the Hyp/+ and +/+ mouse. D-glucose transport did not increase. We conclude that renal adaptation to phosphate deprivation is achieved by modulation of a component of Na+-dependent cotransport in brush border membrane that is not controlled by the X-linked gene.

Microvesicles Bind Soluble Fibrinogen, Adhere to Immobilized Fibrinogen and Coaggregate with Platelets

1998 ◽  
Vol 79 (02) ◽  
pp. 389-394 ◽  
Author(s):  
Nils Olav Solum ◽  
Frank Brosstad ◽  
Turid Pedersen ◽  
Marit Kveine ◽  
Pål André Holme
Keyword(s):  
Flow Cytometry ◽  
Alkaline Phosphatase ◽  
Receptor Complex ◽  
Binding Studies ◽  
Stimulation Of

SummaryIn the present study we have investigated whether platelet derived microvesicles can bind soluble fibrinogen, bind to immobilized fibrinogen, and coaggregate with platelets. Flow cytometry was used for studies on binding of soluble fibrinogen and coaggregation, whereas ELISA wells were used to study binding of microvesicles to immobilized fibrinogen. Biotinylated microvesicles produced by stimulation with A23187, thrombin or SFLLRN of platelets which had been surface-labelled with biotin, were used both for the coaggregation experiments and for the binding studies with immobilized fibrinogen. Unlabelled microvesicles and biotinylated fibrinogen were employed when studying binding of soluble fibrinogen to the microvesicles. For the flow cytometry, the biotinylated proteins were reacted with avidin or streptavidin which was PE-conjugated, whereas the same substances were conjugated with alkaline phosphatase for the ELISA studies. The microvesicles formed after stimulation of platelets by SFLLRN or A23187 clearly bound the soluble, biotinylated fibrinogen. Moreover, isolated biotinylated microvesicles added to washed platelets prior to activation, were associated to the microaggregates that formed after stimulation. A significant binding of biotinylated microvesicles to immobilized fibrinogen could also be detected. The binding of micro-vesicles to soluble and immobilized fibrinogen and association to platelets was clearly specific and at least partly dependent on the GPIIb-IIIa complex, as all of these phenomena could be prevented or reduced by addition of the c7E3 Fab which blocks the activated form of this receptor complex. From these in vitro results it is clear that microvesicles can bind to immobilized fibrinogen, bind soluble fibrinogen and are able to coaggregate with platelets. It may be speculated that these results also reflect a haemostatic role of microvesicles in vivo.

Duodenal brush border intestinal alkaline phosphatase activity affects bicarbonate secretion in rats

2007 ◽  
Vol 293 (6) ◽  
pp. G1223-G1233 ◽  
Author(s):  
Yasutada Akiba ◽  
Misa Mizumori ◽  
Paul H. Guth ◽  
Eli Engel ◽  
Jonathan D. Kaunitz
Keyword(s):  
Alkaline Phosphatase ◽  
Brush Border ◽  
Intestinal Alkaline Phosphatase ◽  
Glycerol Phosphate ◽  
Secretory Rate ◽  
Rat Duodenum ◽  
Ph Stat ◽  
Cystic Fibrosis Transmembrane

We hypothesized that duodenal HCO3− secretion alkalinizes the microclimate surrounding intestinal alkaline phosphatase (IAP), increasing its activity. We measured AP activity in rat duodenum in situ in frozen sections with the fluorogenic substrate ELF-97 phosphate and measured duodenal HCO3− secretion with a pH-stat in perfused duodenal loops. We examined the effects of the IAP inhibitors l-cysteine or l-phenylalanine (0.1–10 mM) or the tissue nonspecific AP inhibitor levamisole (0.1–10 mM) on AP activity in vitro and on acid-induced duodenal HCO3− secretion in vivo. AP activity was the highest in the duodenal brush border, decreasing longitudinally to the large intestine with no activity in stomach. Villous surface AP activity measured in vivo was enhanced by PGE2 intravenously and inhibited by luminal l-cysteine. Furthermore, incubation with a pH 2.2 solution reduced AP activity in vivo, whereas pretreatment with the cystic fibrosis transmembrane regulator (CFTR) inhibitor CFTRinh-172 abolished AP activity at pH 2.2. l-Cysteine and l-phenylalanine enhanced acid-augmented duodenal HCO3− secretion. The nonselective P2 receptor antagonist suramin (1 mM) reduced acid-induced HCO3− secretion. Moreover, l-cysteine or the competitive AP inhibitor glycerol phosphate (10 mM) increased HCO3− secretion, inhibited by suramin. In conclusion, enhancement of the duodenal HCO3− secretory rate increased AP activity, whereas inhibition of AP activity increased the HCO3− secretory rate. These data support our hypothesis that HCO3− secretion increases AP activity by increasing local pH at its catalytic site and that AP hydrolyzes endogenous luminal phosphates, presumably ATP, which increases HCO3− secretion via activation of P2 receptors.

The Role of Polyphenols in the Modulation of Plasma Non-Enzymatic Antioxidant Capacity (NEAC)

2012 ◽  
Vol 82 (3) ◽  
pp. 228-232 ◽  
Author(s):  
Mauro Serafini ◽  
Giuseppa Morabito
Keyword(s):  
Antioxidant Capacity ◽  
Dietary Intervention ◽  
Ex Vivo ◽  
The Body ◽  
Dietary Polyphenols ◽  
Enzymatic Antioxidant ◽  
Endogenous Antioxidant

Dietary polyphenols have been shown to scavenge free radicals, modulating cellular redox transcription factors in different in vitro and ex vivo models. Dietary intervention studies have shown that consumption of plant foods modulates plasma Non-Enzymatic Antioxidant Capacity (NEAC), a biomarker of the endogenous antioxidant network, in human subjects. However, the identification of the molecules responsible for this effect are yet to be obtained and evidences of an antioxidant in vivo action of polyphenols are conflicting. There is a clear discrepancy between polyphenols (PP) concentration in body fluids and the extent of increase of plasma NEAC. The low degree of absorption and the extensive metabolism of PP within the body have raised questions about their contribution to the endogenous antioxidant network. This work will discuss the role of polyphenols from galenic preparation, food extracts, and selected dietary sources as modulators of plasma NEAC in humans.

Anti-obesity role of Aster glehni extract: in vivo and in vitro effects

Planta Medica ◽  
2012 ◽  
Vol 78 (11) ◽  
Author(s):  
HM Lee ◽  
TG Ahn ◽  
CW Kim ◽  
HJ An
Keyword(s):  
In Vitro Effects

A Molecular Approach to Immunoscintigraphy: A Study of the T-Antigen Conformation on the Surface of Tumors

1987 ◽  
Vol 26 (01) ◽  
pp. 1-6 ◽  
Author(s):  
S. Selvaraj ◽  
M. R. Suresh ◽  
G. McLean ◽  
D. Willans ◽  
C. Turner ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Tumor Cell ◽  
T Antigen ◽  
Human Carcinomas ◽  
Animal Tumor ◽  
Synthetic Antigens

The role of glycoconjugates in tumor cell differentiation has been well documented. We have examined the expression of the two anomers of the Thomsen-Friedenreich antigen on the surface of human, canine and murine tumor cell membranes both in vitro and in vivo. This has been accomplished through the synthesis of the disaccharide terminal residues in both a and ß configuration. Both entities were used to generate murine monoclonal antibodies which recognized the carbohydrate determinants. The determination of fine specificities of these antibodies was effected by means of cellular uptake, immunohistopathology and immunoscintigraphy. Examination of pathological specimens of human and canine tumor tissue indicated that the expressed antigen was in the β configuration. More than 89% of all human carcinomas tested expressed the antigen in the above anomeric form. The combination of synthetic antigens and monoclonal antibodies raised specifically against them provide us with invaluable tools for the study of tumor marker expression in humans and their respective animal tumor models.

THYROID STIMULATORS AND THYROID STIMULATION

1971 ◽  
Vol 66 (3) ◽  
pp. 558-576 ◽  
Author(s):  
Gerald Burke
Keyword(s):  
Regulatory System ◽  
Control Site ◽  
Thyroid Cell ◽  
Primary Control ◽  
Physico Chemical ◽  
Site Of Action ◽  
Long Acting

ABSTRACT A long-acting thyroid stimulator (LATS), distinct from pituitary thyrotrophin (TSH), is found in the serum of some patients with Graves' disease. Despite the marked physico-chemical and immunologic differences between the two stimulators, both in vivo and in vitro studies indicate that LATS and TSH act on the same thyroidal site(s) and that such stimulation does not require penetration of the thyroid cell. Although resorption of colloid and secretion of thyroid hormone are early responses to both TSH and LATS, available evidence reveals no basic metabolic pathway which must be activated by these hormones in order for iodination reactions to occur. Cyclic 3′, 5′-AMP appears to mediate TSH and LATS effects on iodination reactions but the role of this compound in activating thyroidal intermediary metabolism is less clear. Based on the evidence reviewed herein, it is suggested that the primary site of action of thyroid stimulators is at the cell membrane and that beyond the(se) primary control site(s), there exists a multifaceted regulatory system for thyroid hormonogenesis and cell growth.

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