Pathophysiology of human proximal tubular transport defects

1982 ◽  
Vol 60 (19) ◽  
pp. 1201-1211 ◽  
Author(s):  
H. C. Gonick
Keyword(s):  
Tubular Transport ◽  
Proximal Tubular

Disorders of tubular electrolyte handling

2020 ◽  
pp. 5112-5123
Author(s):  
Nine V.A.M. Knoers ◽  
Elena N. Levtchenko
Keyword(s):  
Serum Magnesium ◽  
Serum Phosphate ◽  
Magnesium Concentration ◽  
Main Site ◽  
Fanconi’S Syndrome ◽  
Tubular Transport ◽  
Bone Changes ◽  
Proximal Tubular ◽  
Magnesium Excretion ◽  
Fanconi's Syndrome

Glycosuria—glucose reabsorption in the proximal tubule is carried out by two different pairs of apical Na+-dependent (SGLT1 and -2) and basolateral Na+-independent (GLUT1 and -2) glucose transporters. Abnormalities in renal glucose transport can be seen in association with other defects of proximal tubular transport. Familial renal glycosuria is a rare autosomal recessive condition caused by mutations in the SGLT2-encoding gene, SLC5A2. Phosphate-handling disorders—the plasma concentration of inorganic phosphate depends on the balance between intestinal absorption, renal excretion, and the internal contribution from bone. Changes of serum phosphate levels can be caused by numerous inherited and acquired conditions. Disorders associated with increased urinary phosphate excretion and low serum phosphate levels produce symptoms that mainly affect the bones: rickets in children and osteomalacia in adults. Magnesium-handling disorders—normal plasma magnesium concentration is achieved by variation of urinary magnesium excretion in response to altered uptake by the intestine. The main site of magnesium absorption is the small bowel, via paracellular simple diffusion at high intraluminal concentrations, and via active transcellular uptake through the magnesium channel TRPM6 at low concentrations. Regulation and fine-tuning of serum magnesium concentration occurs primarily in the kidney. Genetic disorders of magnesium handling include Gitelman’s syndrome. Aminoaciduria and renal Fanconi’s syndrome—most amino acids (except for tryptophan, which is protein bound) are freely filtered by the glomerulus, after which 95 to 99.9% are reabsorbed in the proximal tubules by apical Na+-dependent cotransporters and Na+-independent cotransporters. Aminoaciduria is defined as urinary excretion of more than 5% of the filtered load of an amino acid. Renal Fanconi’s syndrome is characterized by a generalized defect of both Na+-coupled and receptor-mediated proximal tubular transport.

Autoradiographic study of Diodrast-I131 transport in Necturus kidney

1960 ◽  
Vol 199 (5) ◽  
pp. 931-941 ◽  
Author(s):  
William B. Kinter ◽  
Lucian L. Leape ◽  
Jordan J. Cohen
Keyword(s):  
Autoradiographic Study ◽  
Intracellular Concentration ◽  
Tubular Cells ◽  
Different Types ◽  
Tubular Transport ◽  
Proximal Tubular ◽  
Renal Tubular Transport ◽  
Arterial Plasma ◽  
Renal Tubular ◽  
Bidirectional Movement

Renal tubular transport of Diodrast-I131 was studied in Necturus by newly devised autoradiographic methods used in conjuction with classical clearance methods. Clearance measurements on individual animals indicate different types of over-all tubular transport ranging from secretion into tubular urine, heretofore reported in many species, to reabsorption out of tubular urine, so far reported only in Necturus. Diodrast content of tubular urine as disclosed by autoradiography both corroborates clearance data and provides evidence that proximal tubules are the major site of Diodrast transport irrespective of direction. This view is supported by inulin-C14 autoradiographs. In addition, significant amounts of Diodrast were accumulated within proximal tubular cells during all types of transport. With less than 3 mg Diodrast/100 ml arterial plasma, the estimated intracellular concentration ranged from 2 to 19 times that in plasma. At higher plasma levels, tubular transport was overwhelmed and intracellular concentration no longer exceeded that in plasma. These results support a previously formulated theory of simultaneous, bidirectional movement of Diodrast across tubular cells in Necturus kidney.

Effect of parathyroid hormone on renal tubular permeability

1976 ◽  
Vol 231 (5) ◽  
pp. 1401-1407 ◽  
Author(s):  
WB Lorentz
Keyword(s):  
Parathyroid Hormone ◽  
Active Transport ◽  
Intravenous Infusion ◽  
Rat Kidney ◽  
Tubular Transport ◽  
Proximal Tubular ◽  
Renal Tubular ◽  
Tubular Permeability

The effect of parathyroid hormone (PTH) on renal tubular permeability has been studied utilizing micropuncture techniques in the rat kidney. After microinjection into superificial nephrons during control conditions, inulin (98.8 +/- 2.7%) and mannitol (97.2 +/- 2.4%) recovery from the experimental kidney was essentially complete. During intravenous infusion of PTH, inulin (99.3 +/- 2.9%) recovery was again complete. Mannitol recovery decreased signficantly after both early-proximal (84.7 +/- 5.8%, P less than 0.001) and late-proximal (89.7 +/- 2.8%, P less than 0.001) injections. There was no loss of either mannitol or inulin following distal tubular injection. Late-proximal TF/P inulin ratios during control conditions were 2.10 +/- 0.20 and decreased insignificantly to 1.99 +/- 0.21 during PTH infusion. Late-proximal TF/P mannitol rations were 2.09 +/- 0.21 during control periods and during PTH infusion decreased significantly to 1.78 +/- 0.19 (P less than 0.001). These results indicate that PTH induces a change in proximal tubular permeability to a usually impermeable nonelectrolyte, mannitol. The effects of PTH on proximal tubular transport could be partially explained by this alteration in permeability, which would increase passive backflux of actively transported species and decrease net transport while having no effect on active transport.

Proximal tubular transport and urinary excretion of sodium after renal denervation in sodium depleted rats

1985 ◽  
Vol 403 (2) ◽  
pp. 146-150 ◽  
Author(s):  
G�bor Sz�n�si ◽  
P�l Benes�th ◽  
Lajos Tak�cs ◽  
Bozena Asztalos ◽  
M�ria Vedres
Keyword(s):  
Urinary Excretion ◽  
Renal Denervation ◽  
Tubular Transport ◽  
Proximal Tubular

Renal expression of sodium transporters and aquaporin-2 in hypothyroid rats

2003 ◽  
Vol 284 (5) ◽  
pp. F1097-F1104 ◽  
Author(s):  
Roland Schmitt ◽  
Enno Klussmann ◽  
Thomas Kahl ◽  
David H. Ellison ◽  
Sebastian Bachmann
Keyword(s):  
Clinical Symptoms ◽  
Transport Proteins ◽  
Na Channel ◽  
Kidney Size ◽  
Renal Handling ◽  
Aquaporin 2 ◽  
Tubular Transport ◽  
Proximal Tubular ◽  
Type 3

Hypothyroidism is associated with significant abnormalities in the renal handling of salt and water. To address the involvement of tubular transport proteins in these abnormalities, rats were rendered pharmacologically hypothyroid and the abundance of major tubular transport proteins was assessed by immunoblot and immunohistochemistry. Hypothyroidism resulted in a marked reduction in kidney size and creatinine clearance along with decreased or unchanged total kidney abundance of the transport proteins. Whereas the proximal tubular type 3 Na/H exchanger (NHE3) and type 2 Na-phosphate cotransporter (NaPi2) stood out by their disproportionately reduced abundance, the bumetanide-sensitive type 2 Na-K-2Cl cotransporter (NKCC2) and aquaporin-2 (AQP2) were unaltered in their total kidney abundance despite a markedly lower kidney mass. The latter proteins in fact showed enhanced immunostaining. Decreased NHE3 and NaPi2 expression was most likely due to a combination of triiodo-l-thyronine (T3) deficiency along with a reduced glomerular filtration rate. The increased abundance of NKCC2 and AQP2 may have been caused by an increased action of vasopressin since urinary excretion of this hormone was elevated. On the other hand, the thiazide-sensitive Na-Cl cotransporter; the α-, β-, and γ-subunits of the amiloride-sensitive epithelial Na channel; and the α1-subunit of Na-K-ATPase showed a moderate decrease in total kidney abundance that was largely proportional to the smaller kidney mass. Although the observed expression of transporters was associated with a balanced renal sodium handling, altered transporter abundance may become functionally relevant if the hypothyroid kidney is challenged by an additional destabilization of the milieu interieur that has previously been shown to result in an inadequate natriuresis and clinical symptoms.

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