engleski

Role of hepatic and renal sat-1 in ethylene glycol-induced urolithiasis in rat

INTRODUCTION. Sodium-independent sulfate anion transporter (sat-1 ; Slc26a1) plays a major role in transport of oxalate (OX) across the cell membrane by exchanging OX for sulfate or bicarbonate. Sat-1 mRNA has been detected strongly in liver and kidney and weakly in few other organs in rats, mice, and humans. By immunocytochemistry (IC), the protein has been localized in rats to the sinusoidal membrane of hepatocytes and basolateral membrane of proximal tubules (PT) in the kidney cortex, with the male (M)-dominant expression. In liver, which is a major OX producer, sat-1 mediates the extrusion of OX and uptake of sulfate, whereas in PT, it mediates the OX uptake, mainly in exchange for intracellular sulfate. In middle-aged humans, OX is a major cause of sex-related urolithiasis ; men excrete more OX and have higher incidence of OX stones then women. Accordingly, in studies of experimental urolithiasis in ethylene glycol (EG)-treated rats, testosterone stimulated, whereas female (F) sex hormones inhibited the urine excretion of OX and formation of OX stones. The role of OX transporters that in liver and kidneys exhibit the sex-related expression, such as sat-1, in the development of OX urolithiasis is not known. In the present study, we tested the expression of sat-1 at the protein and mRNA levels in the liver and kidneys of EG-treated rats. METHODS. Adult M and female (F) Wistar strain rats were treated with EG (0, 75% v/v in drinking water) for one month. Controls drunk water without EG. 24-h urine was collected in metabolic cages a day before sacrificing. OX in the blood plasma and urine were determined by ion-chromatography. Tissue morphology and OX crystals in the urine sediment were checked by light microscopy. Sat-1 protein expression was studied using a polyclonal antibody by IC in p-formaldehyde-fixed tissue cryosections, and by Western blotting of total cell membranes isolated from tissue homogenates. Tissue expression of sat-1 mRNA was studied by real time RT-PCR. RESULTS. In control M and F animals, the M-dominant sex differences in the urine excretion of OX, in the number and size of urine OX crystals, and in the expression of sat-1 protein (but not mRNA) in liver and kidneys, were confirmed. Compared to controls, the EG-treated animals exhibited: a) in plasma, 100% (F) and 4-fold (M) higher concentration of OX, b) in urine, 100% (F) and 17-fold (M) higher OX excretion, c) in urine sediment, similar and low abundance of small OX crystals in F, and increased abundance of large OX crystals in M, d) in tissues of both sexes, un-affected morphology in liver, and dilatated PT and distended peritubular spaces in kidneys, e) upregulated expression of sat-1 protein in the F liver and kidneys to the level in M organs, f) unchanged expression of sat-1 protein in the M liver and kidneys, and g) unchanged expression of sat-1 mRNA in both organs of F and M animals. CONCLUSION. Whereas the blood and urinary parameters in EG-treated rats indicate the low and high oxaluric state in F and M rats, respectively, the EG-induced elevated expression of sat-1 protein in the F liver and kidneys, and unchanged expression of this protein in M organs, indicate that sat-1 plays no significant role in generation of OX urolithiasis in EG-treated animals.

gender differences; oxalate; oxaluria; sex differences; eksperimental urolithiasis

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