Theories on the Mechanism of Action of 1,25(OH)3D3 on Active Intestinal Calcium and Inorganic Phosphate Absorption: are the Calcium and Phosphate Transport Processes Coupled, Uncoupled or Both?

1979 ◽  
pp. 687-692
Keyword(s):  
Mechanism Of Action ◽  
Inorganic Phosphate ◽  
Phosphate Transport ◽  
Transport Processes ◽  
Phosphate Absorption

Characteristics of phosphate transport in isolated proximal tubule

1976 ◽  
Vol 231 (3) ◽  
pp. 979-985 ◽  
Author(s):  
VW Dennis ◽  
PB Woodhall ◽  
RR Robinson
Keyword(s):  
Proximal Tubule ◽  
Inorganic Phosphate ◽  
Phosphate Transport ◽  
Phosphate Concentration ◽  
Proximal Tubules ◽  
Rabbit Serum ◽  
Phosphate Absorption ◽  
Glomerular Filtrate ◽  
Straight Portion ◽  
The Mean

The characteristics of inorganic phosphate transport in isolated perfused proximal tubules of the rabbit were examined using radioisotopic techniques. When tubules were perfused with an ultrafiltrate of rabbit serum, the mean lumen-to-bath flux of phosphate in the convoluted segment was 6.60 +/- 1.41 (SE) pmol/mm-min with a simultaneous back-to-lumen flux of 0.45 +/- 0.08. In the straight portion of the proximal tubule, the lumen-to-bath flux was significantly lower (P less than 0.01) at 2.22 +/- 0.48 pmol/min-min with a bath-to-lumen flux of 0.31 +/- 0.05. The lumen-to-bath flux was not affected by increases in the intraluminal phosphate concentration from 2.00 +/- 0.19 to 3.12 +/- 0.34 mM or by the isohydric replacement of bicarbonate in the ambient fluids with chloride. However, phosphate absorption was completely inhibited by ouabain 10(-5) M in the bath. These data indicate that phosphate absorption in these segments occurs by a mechanism other than independent diffusion and is saturated at phosphate concentrations characteristic of normal glomerular filtrate. There is no evidence for significant phosphate transport from bath to lumen.

Phosphate Transport Processes of Animal Cells

1982 ◽  
pp. 645-663 ◽  
Author(s):  
Peter L. Pedersen ◽  
Janna P. Wehrle
Keyword(s):  
Phosphate Transport ◽  
Transport Processes ◽  
Animal Cells

Stanniocalcin: a novel protein regulating calcium and phosphate transport across mammalian intestine

1998 ◽  
Vol 274 (1) ◽  
pp. G96-G102 ◽  
Author(s):  
Karen L. Madsen ◽  
Michele M. Tavernini ◽  
Christine Yachimec ◽  
Donna L. Mendrick ◽  
Pedro J. Alfonso ◽  
...  
Keyword(s):  
Calcium Absorption ◽  
Short Circuit ◽  
Regulatory Protein ◽  
Chinese Hamster ◽  
Phosphate Transport ◽  
Simultaneous Increase ◽  
Rat Intestine ◽  
Glycoprotein Hormone ◽  
Phosphate Absorption ◽  
Ussing Chambers

Stanniocalcin (STC) is an anti-hypercalcemic glycoprotein hormone previously identified in the corpuscles of Stannius in bony fish and recently in the human genome. This study undertook to express human STC in Chinese hamster ovary (CHO) cells and to determine its effects on calcium and phosphate absorption in swine and rat intestine. Unidirectional mucosal-to-serosal ( J m→s) and serosal-to-mucosal ( J s→m)45Ca and32P fluxes were measured in vitro in duodenal tissue in voltage-clamped Ussing chambers. Addition of STC (10–100 ng/ml) to the serosal surface of the duodenum resulted in a simultaneous increase in calcium J m→s and J s→mfluxes, with a subsequent reduction in net calcium absorption. This was coupled with an STC-stimulated increase in phosphate absorption. Intestinal conductance was increased at the highest dose of STC (100 ng/ml) in swine tissue. The addition of STC to the mucosal surface had no effect on calcium and phosphate fluxes. STC at doses of 10–1,000 ng/ml had no effect on short-circuit current in any region of the rat intestine. In conclusion, human recombinant STC decreases the absorption of calcium and stimulates the absorption of phosphate in both swine and rat duodenum. STC is a novel regulatory protein that regulates mammalian intestinal calcium and phosphate transport.

Sodium, potassium, and intestinal transport of glucose, l-tyrosine, phosphate, and calcium

1963 ◽  
Vol 205 (1) ◽  
pp. 107-111 ◽  
Author(s):  
Harold E. Harrison ◽  
Helen C. Harrison
Keyword(s):  
Small Intestine ◽  
Calcium Transport ◽  
Inorganic Phosphate ◽  
Choline Chloride ◽  
Sodium Concentration ◽  
Phosphate Transport ◽  
Metabolic Energy ◽  
Transport Systems ◽  
Bicarbonate Buffer ◽  
Distal Small Intestine

Everted loops of rat small intestine were incubated in media varying in their concentrations of sodium and potassium. Reduction of sodium concentration was effected by substitution of choline chloride in equimolar amounts for sodium chloride in the saline-bicarbonate buffer. Concentrative transport of glucose, l-tyrosine, inorganic phosphate, and calcium was measured by determination of the final ratio of the concentrations of the solute in serosal and mucosal fluids, and the increment of the solute in serosal fluid during incubation. Ca45 was used as an indicator of calcium distribution. The glucose, l-tyrosine, and inorganic phosphate transport systems require sodium, and at a submaximal concentration of sodium an increased concentration of potassium is inhibitory. The calcium transport system does not require sodium and in loops from the distal small intestine calcium transport is enhanced by reduction of sodium concentration in the medium. It is postulated that there is a common sodium-requiring system which is necessary for the linkage of metabolic energy to glucose, amino acid, and inorganic phosphate transport.

HOMEOSTATIC ADJUSTMENT IN THE RENAL TUBULAR TRANSPORT OF INORGANIC PHOSPHATE IN THE DOG

1955 ◽  
Vol 33 (1) ◽  
pp. 638-650 ◽  
Author(s):  
James G. Foulks
Keyword(s):  
Inorganic Phosphate ◽  
Renal Tubule ◽  
Phosphate Transport ◽  
Sodium Sulphate ◽  
Tubular Transport ◽  
Renal Tubular Transport ◽  
Transport Of Inorganic Phosphate ◽  
Renal Tubular ◽  
Filtered Load

By means of the infusion of small amounts of sodium sulphate it has been possible to elevate the filtered load of inorganic phosphate to the renal tubule in fasted dogs without the administration of exogenous phosphate. Under these circumstances, the reabsorption of phosphate remains virtually complete, even when filtered loads are reached which result in a substantial phosphaturia when phosphate has been administered. By comparing phosphate reabsorption and excretion in fasted animals, and in animals at various intervals after feeding, the existence of homeostatic adjustments in the renal tubular transport of inorganic phosphate has been demonstrated. The available evidence suggests that the intracellular disposition of phosphate itself may be an important factor in determining the rate of renal tubular phosphate transport at filtered loads in the physiological range. The limitations of the determination of the phosphate "Tm" as a device for studying homeostatic processes have been discussed.

Does Availability of Inorganic Phosphate Regulate Cellular Oxidative Metabolism?

Physiology ◽  
1986 ◽  
Vol 1 (3) ◽  
pp. 100-103 ◽  
Author(s):  
PC Brazy ◽  
LJ Mandel
Keyword(s):  
Solute Transport ◽  
Oxidative Metabolism ◽  
Inorganic Phosphate ◽  
Phosphate Transport ◽  
Renal Tubules ◽  
Metabolic Processes

Cells require inorganic phosphate for formation of ATP and a variety of other metabolic and transport functions. Studies of renal tubules indicate that availability of phosphate does regulate rates of oxidative metabolism and solute transport, that intracellular metabolic processes compete for inorganic phosphate, and that transepithelial phosphate transport provides inorganic phosphate for use within the cell.

HOMEOSTATIC ADJUSTMENT IN THE RENAL TUBULAR TRANSPORT OF INORGANIC PHOSPHATE IN THE DOG

1955 ◽  
Vol 33 (4) ◽  
pp. 638-650 ◽  
Author(s):  
James G. Foulks
Keyword(s):  
Inorganic Phosphate ◽  
Renal Tubule ◽  
Phosphate Transport ◽  
Sodium Sulphate ◽  
Tubular Transport ◽  
Renal Tubular Transport ◽  
Transport Of Inorganic Phosphate ◽  
Renal Tubular ◽  
Filtered Load

By means of the infusion of small amounts of sodium sulphate it has been possible to elevate the filtered load of inorganic phosphate to the renal tubule in fasted dogs without the administration of exogenous phosphate. Under these circumstances, the reabsorption of phosphate remains virtually complete, even when filtered loads are reached which result in a substantial phosphaturia when phosphate has been administered. By comparing phosphate reabsorption and excretion in fasted animals, and in animals at various intervals after feeding, the existence of homeostatic adjustments in the renal tubular transport of inorganic phosphate has been demonstrated. The available evidence suggests that the intracellular disposition of phosphate itself may be an important factor in determining the rate of renal tubular phosphate transport at filtered loads in the physiological range. The limitations of the determination of the phosphate "Tm" as a device for studying homeostatic processes have been discussed.

Presence of multiple sodium-dependent phosphate transport processes in proximal brush-border membrane

1987 ◽  
Vol 252 (2) ◽  
pp. F226-F231 ◽  
Author(s):  
J. J. Walker ◽  
T. S. Yan ◽  
G. A. Quamme
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Phosphate Transport ◽  
Transport Processes ◽  
Proximal Tubules ◽  
High Affinity ◽  
Medullary Tissue ◽  
Sodium Dependent ◽  
Early Proximal Tubule

Renal brush-border membrane phosphate transport was studied in early and late segments of the pig proximal tubule. Vesicles were prepared from early proximal tubules (outer cortical tissue) and late proximal tubules (outer medullary tissue). Sodium-dependent phosphate uptake into brush-border membrane vesicles was determined using voltage clamp at 5-6 s, 21 degrees C. Sodium-dependent D-glucose uptake was determined to verify the cortical and medullary tissue cuts. At pH 8.0 (pHi = pHo), two sodium-dependent phosphate transport systems were evident in the early proximal tubule: a high-affinity system [Km, 0.06 +/- 0.01 mM; maximal transport activity (Vmax), 3.6 +/- 1.1 nmol X mg protein-1 X min-1] and a low-affinity system (Km, 4.11 +/- 0.02 mM; Vmax, 9.7 +/- 0.7 nmol X mg protein-1 X min-1). In the late proximal tubule at pH 8.0, only a single high-affinity transport process (Km, 0.19 +/- 0.7 mM; Vmax, 3.4 +/- 0.5 nmol X mg protein-1 X min-1) was evident. D-Glucose kinetics at pH 7.0 revealed both a high-affinity (Km, 0.55 +/- 0.09 mM) and a low-affinity (Km, 20.09 +/- 1.39 mM) system in the early proximal segment and a single high-affinity (Km, 1.27 +/- 0.36 mM) process in the late segment. These data suggest that two systems, distinct in their affinities and capacities, are involved in both D-glucose and phosphate transport across the brush-border membrane of the early proximal tubule, but that only a single high-affinity system is present in the late segment.

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