Presence of organic anion transporters 3 (OAT3) and 4 (OAT4) in human adrenocortical cells.

Since the organic anion transporter-1 (OAT1) has been implicated in cortisol release from bovine and rat adrenal zona fasciculata cells, we addressed the question of whether OATs are present in human adrenal cortical cells. In the human adrenal cell line NCI-H295R, 24-h cortisol secretion increased up to 30-fold on exposure to forskolin. Incubation of forskolin-treated cells for 24 h with the OAT substrates probenecid, p-aminohippurate (PAH), glutarate or cimetidine inhibited cortisol release partly. RT-PCR did not reveal expression of human OAT1 and OAT2, but OAT3 and OAT4 mRNAs were detected in both NCI-H295R cells and human adrenal tissue. When human OAT3 (hOAT3) and hOAT4 were expressed in Xenopus laevis oocytes, only hOAT3 showed [3H]cortisol uptake in excess of that of water-injected control oocytes. Cortisol uptake via OAT3 was saturable with an apparent Kt of 2.4 microM. In NCI-H295R cells, [3H]estrone sulphate uptake was saturable, cis-inhibited by OAT substrates and trans-stimulated by preloading with glutarate or cortisol. Likewise, [3H]PAH uptake was cis-inhibited by estrone sulphate and trans-stimulated by preloading the cells with PAH, glutarate or cortisol, indicating functional expression of OATs in the plasma membrane of NCI-H295R cells.

Osmoregulation of aldose reductase and sorbitol dehydrogenase in cultivated interstitial cells of rat renal inner medulla.

BACKGROUND: Little is known about sorbitol metabolism in renal papillary interstitial cells. For characterization we studied regulation of sorbitol synthesis by aldose reductase (AR) and degradation by sorbitol dehydrogenase (SDH) in papillary interstitial cells. METHODS: Interstitial cells were isolated from rat renal inner medulla to a pure cell fraction. mRNA was isolated from cultivated cells and sorbitol, AR and SDH activity were determined enzymatically in homogenates. RESULTS: Sorbitol concentration in these cells at 300 mosmol/l was 4.4+/-0.3 vs 78+/-3.6 micro mol/g protein at 600 mosmol/l. At steady-state conditions at 300 mosmol/l, AR activity was nearly the same as SDH activity (15.1+/-1.6 vs 16.6+/-2.0 U/g protein). At 600 mosmol/l, AR activity increased to 82.5+/-11.4 U/g protein and SDH activity to 31.5+/-6.0 U/g protein. Studying the time course of enzyme activity after changing osmolarity from 300 to 600 mosmol/l, we found half maximal stimulation after 2-3 (AR) or 3 (SDH) days. The amount of AR-mRNA preceded the rise of enzyme activity, whereas SDH-mRNA was not significantly influenced. Lowering osmolarity from 600 to 300 mosmol/l, enzyme activity decreased to less than half within 2 (AR) or 1 (SDH) day(s). CONCLUSIONS: The results suggest that sorbitol metabolism contributes to handling of osmotic stress in rat renal papillary interstitial cells.

Tuberculous meningitis in a renal transplant recipient.

Tuberculous meningitis is a very rare, but serious extrapulmonary complication of mycobacterial infections in immunocompromised patients, such as organ transplant recipients. We describe here a 66-year-old Turkish woman without any history of tuberculosis, who received a renal allograft transplant in 1994. After a pilgrimage to an endemic area for tuberculosis, she presented with fever and headache in August 1998. Clinical examination revealed positive meningism and hyperreflexia. Lymphocytosis was noted in her cerebrospinal fluid (CSF) and Mycobacterium tuberculosis infection was detected by PCR within the CSF. Despite immediate triple antituberculosis therapy, the patient's clinical condition deteriorated rapidly, with the development of septic shock syndrome, and she died three weeks after admission due to cardiovascular and respiratory failure. Mycobacterial infections, including extrapulmonary manifestations, should thus be considered in all renal transplant recipients presenting with unexplained fever. Preventive therapy, i.e. isoniazid prophylaxis, may also be recommended for patients risking exposure in areas endemic for tuberculosis.

Sorbitol transport in rat renal inner medullary interstitial cells.

BACKGROUND: Sorbitol plays an important role in renal osmoregulation. In the rat renal inner medulla sorbitol synthesis and sorbitol degradation are located in different cell types. Whereas sorbitol synthesis can be detected in the inner medullary collecting duct cells, sorbitol degradation takes place in the interstitial cells. Therefore, one can speculate that the cooperation between epithelial and interstitial cells requires sorbitol transport into interstitial cells. METHODS: Our studies were performed with an interstitial cell line derived from the renal inner medulla of Wistar rats. These cells have typical characteristics of renal fibroblasts. In addition, they possess a high activity of sorbitol dehydrogenase as determined in vivo. Uptake was measured by liquid scintillation counting. For studies on sorbitol metabolism sorbitol concentration was measured photometrically. RESULTS: The results show that sorbitol transport into interstitial cells occurs via a yet to be described transport system. No saturation of sorbitol transport could be found up to an extracellular sorbitol concentration of 80 mmol/L. The transport was neither sodium nor chloride dependent. Trans-stimulation increased the sorbitol uptake. Sorbitol uptake was less inhibited by cytochalasin B than 2-deoxy-D-glucose uptake. The transport showed a high affinity for sorbitol and only little inhibition of sorbitol uptake by substances with a similar structure was observed. CONCLUSIONS: Our results show a new sorbitol transport system in renal inner medullary interstitial cells, which is rather different from the described sorbitol permease in renal epithelial cells and from glucose transporters of the GLUT- and SGLT-family.