Effective use of renal cortical slices in transport and metabolic studies

Immunocytochemical characterization of the incubated rat renal cortical slices

The use of renal cortical slices in vitro and the data obtained in these studies have been subjects of controversy, largely due to uncertain viability, e.g., structural and functional integrity of the proximal and other tubules. However, detailed studies of tubule integrity have not been reported. To correlate functional and structural viability of the hand-cut rat renal cortical slices, incubated in optimally conditioned media for up to 25 h, we studied the time course of p-aminohippurate (PAH) uptake, the immunocytochemical distribution of several proteins that reside in the proximal tubule basolateral [Na/K-ATPase, organic anion transporters (OAT)1 and OAT3], or brush border [megalin, sodium-proton exchanger (NHE)3] membrane, as well as the general integrity of the tubule epithelium and its cytoskeleton (actin filaments, microtubules). PAH uptake in slices was proportional to time within 1 h of incubation and gradually declined thereafter. The immunostaining experiments indicated a fast, time-dependent loss of basolateral transporters, at a rate of OAT1 > Na/K-ATPase > OAT3. In the brush border membrane, the loss of megalin was faster than that of NHE3, and a partial redistribution of NHE3 into the basolateral domain indicated the loss of cell polarity. The loss of intracellular actin and tubulin cytoskeleton in the proximal tubule was already visible after 15 min of incubation and gradually increased with time, whereas a partial redistribution of actin to the basolateral domain indicated a compromised polarity of the cells. The data also revealed very early (after 15 min) necrotic events in the proximal tubule epithelium, with sloughing of brush border and cell debris into the tubule lumen, detachment of cells from the basal membrane, and opening and widening of the tubule lumen. We conclude that the loss of cellular structure, cytoskeleton, and cell membrane transporters in the nephron epithelium is a very early event in the incubated rat renal cortical slices.

Transport of vitamin C in animal and human cells

The transport systems of animal and human tissues for vitamin C are reviewed with respect to their properties. It emerges that pure diffusion plays only a very minor role while a variety of more or less specific transporters is found on cellular membranes. Although most tissues prefer the reduced ascorbate over the oxidized dehydroascorbic acid and have high-affinity transporters for it, there are several examples for the reversed situation. Special attention is given to similarity or identity with glucose transporters, especially the GLUT-1 and the sodium-dependent intestinal and renal transporters, and to the very widespread dependence of ascorbate transport on sodium ions. The significance of ascorbate transport for vitamin C-requiring and nonrequiring species as well as alterations in states of disease can be seen from ample experimental evidence.

Susceptibility of ageing kidney to quinidine

Male Fischer-344 rats aged 3-4 months and 30-32 months were used in this study. Quinidine in vitro reduced accumulation of organic ions, p-ammonium hippurate (PAH) and tetraethyl ammonium (TEA), inhibited oxygen consumption and increased LDH leakage, in renal cortical slices. High concentrations of quinidine (2 and 3 mmol l-1) produced overt toxicity and no age related differences in any of the parameters measured were observed. But at lower concentrations significant age-related differences in kidney susceptibility to quinidine were evident. Administration of 75 mg kg-1 day-1 quinidine for 4 days caused exacerbated renal damage in senescent rats compared to young adults as demonstrated by greater elevation of blood urea nitrogen and serum creatinine, and greater inhibition of TEA uptake in renal cortical slices. These results establish significant age related differences in renal damage due to quinidine.

Glomerular podocytes in cultured rat kidney slices. A qualitative and quantitative electron-microscopic study

The ultrastructure of rat glomerular epithelial cells (podocytes) in kidney slices in vitro was examined using qualitative and quantitative electron microscopy. The kidney slices were cultured in Medium 199 with Hanks' salts in a 5% CO2/95% O2 environment for up to 14 days. Few changes in podocyte ultrastructure occurred in the first 12 h of culture, but by 24 h cell bodies were rounded, microvilli were present on all podocyte surfaces, and some foot processes had been replaced by flattened expanses of cytoplasm. These changes were more pronounced by 3 days, when some podocytes had developed pseudopodal extensions and appeared to be migrating from glomeruli onto the slice surface. Podocytes could still be identified after 8, 10 and 14 days of culture, although relatively few glomeruli remained at 14 days. Morphometric methods were used to analyse podocyte shape, volume and surface area during the first 4 days of culture. The most significant change involved loss of foot processes: the number of filtration slits per 100 microns of basement membrane decreased from 211.8 +/- 15.0 (mean +/- SD) at the commencement of culture, to 55.3 +/- 22.6 after 2 days (p less than 0.001). These data provide baseline information for in vitro studies on the effects of nephrotoxins on podocytes.

Effects of cadmium-metallothionein on renal organic ion transport and lipid peroxidation in rats

The effects of cadmium-metallothionein (Cd-MT) on organic ion uptake in renal cortical slices and lipid peroxidation in the kidney were studied in rats. For in vitro studies, slices were prepared from kidneys of control animals and incubated in buffer containing either cadmium chloride (CdCl2) or Cd-MT in equimolar Cd concentrations ranging from 5 x 10(-6) to 2 x 10(-4) M. Uptake into the slices of the organic anion p-aminohippuric acid (PAH) was found to be inhibited by both forms of Cd in a dose-dependent manner. Although this inhibition was slightly greater in the presence of Cd-MT, accumulation of Cd into the slices was approximately 12 times greater with CdCl2 than Cd-MT. Tetraethylammonium (TEA) uptake was less sensitive to the inhibitory effects of both CdCl2 and Cd-MT, although a dose-dependent inhibition did occur with higher Cd concentrations. To study the in vivo effects of Cd-MT on transport function and lipid peroxidation in the kidney, rats were injected with Cd-MT (0.3 mg Cd per kilogram body weight [bw]) and sacrificed at specific time intervals. Similar to the in vitro studies, PAH uptake into the renal cortical slices was markedly inhibited within 12 hours after Cd-MT injection whereas inhibition of TEA uptake was less and not observed until 48 hours after injection. Only a small increase (1.4-fold) in lipid peroxidation, as measured by generation of malondialdehyde (MDA), in the kidney was detected at four hours postinjection, and no further increase was observed at later time periods. The results suggest that Cd-MT affects the transport of organic anions and cations during its renal uptake but that lipid peroxidation may play only a minor role in Cd-MT-induced renal toxicity.

The volume and ionic composition of cells in incubated slices of rat renal cortex, medulla and papilla

The apparent extracellular space in incubated slices of rat renal cortex, medulla and papilla has been measured using three differently sized marker molecules, mannitol, sucrose and inulin. Cellular volumes have been estimated by following the efflux of 3-O-methyl-D-glucose from equilibrated slices. Sucrose appears to be the most accurate extracellular marker in each of the regions examined, in that the sum of its volume of distribution plus cellular volume approximates most closely to the total slice fluid volume. Inulin has the same volume of distribution as sucrose in cortical slices, but under-penetrates medullary and papillary tissue. Mannitol overestimates the extracellular space in all three regions, although its larger volume of distribution, relative to that of sucrose, was not statistically significant in papillary slices. When cell volume and composition are estimated (a) using sucrose as extracellular marker and (b) making appropriate allowance for the presence of bound tissue electrolytes, it is found that cells in each region have low Na+ and high K+ concentrations and contents. When papillary slices are incubated in medium of very high osmolality (NaCl plus urea, 2000 mosmol/kg H2O) there is a moderate (approx. 23%) decrease in cell volume and an increase in cell fluid Na+ and Cl- concentrations equal to approx. 50% of the increase in the extracellular concentrations. Cell K+ concentrations remain unchanged. The results show that cells in renal slices are able to maintain high K+-to-Na+ ratios when incubated in isosmotic (cortex) or moderately hyperosmotic media (medulla and papilla), and suggest that regulation of papillary cell volume following hyperosmotic shock can only partly be ascribed to uptake of extracellular electrolytes.