[Distribution of some hydrolases in the rat kidney (author's transl)]

Primary culture of proximal tubular cells from normal rat kidney as an in vitro model to study mechanisms of nephrotoxicity. Toxicity of nephrotoxicants at low concentrations during prolonged exposure

The aim of this study was to set up an in vitro system to study nephrotoxicity of xenobiotics which allows exposure at low concentrations for long periods (1-5 days). A very pure preparation of isolated proximal tubular cells (PTC) from rat kidney (Boogaard et al., Toxicol Appl Pharmacol 101: 135-143, 1989) was brought into primary culture. Cells grew to confluence in 3 days and could be maintained up to 8 days in a modification of Dulbecco's modified Eagle's medium Ham F12 nutrient mixture supplemented with fetal calf serum. Fibroblast growth was completely suppressed by replacement of L-valine by D-valine and of L-arginine by L-ornithine. Polarity was retained: in cells grown on filters organic anions were transported at the basolateral membrane while D-glucose transport was located at the apical membrane. Inhibition of the latter was used to assess the functional integrity of the cells after exposure to nephrotoxins. The newly grown cells expressed gamma-glutamyltranspeptidase activity since incubation with the glutathione-conjugate of 1,1-dichloro-2,2-difluoroethylene (DCDFE) induced cytotoxicity. Both beta-lyase and acylase activities were expressed because the cysteine-S-conjugate and the corresponding mercapturate of DCDFE showed cytotoxicity. Cultured cells showed toxicity on prolonged exposure to very low concentrations of gentamicin, cephaloridine, cisplatin and the cysteine-S-conjugate of chlorotrifluoroethylene. The lowest concentrations at which toxicity can be observed are 1-3 orders of magnitude lower in primary cultures than in freshly isolated PTC in suspension. This indicates that this cell model is suitable to investigate mechanisms of nephrotoxicity in vitro, at prolonged exposure to the low concentrations that are relevant in vivo levels.

Isolated proximal tubular cells from rat kidney as an in vitro model for studies on nephrotoxicity. I. An improved method for preparation of proximal tubular cells and their functional characterization by alpha-methylglucose uptake

Rat renal proximal tubular cells were isolated by successive EGTA and collagenase perfusions and purified by filtration and isopycnic centrifugation. The method is rapid and provides a much higher fraction of proximal tubular cells (90-95%) than comparable methods. The yield of viable (97 +/- 3%) cells is high (30 X 10(6) cells/g kidney). The intracellular ATP was 16 +/- 2 nmol/mg protein and remained essentially constant for at least 3 hr. The cells were characterized for transport of organic ions and glucose. Glucose transport was studied by alpha-[14C]methylglucose uptake; apparent Km and Vmax values were 3.4 +/- 0.5 mM and 4.1 +/- 0.9 nmol/min.mg protein, respectively. This transport could almost be completely inhibited by phloridzin, indicating that the uptake is mediated by the brush border glucose carrier.

Lysosomes of the renal cortex: heterogeneity and role in protein handling

Rate sedimentation of the kidney cortical mitochondrial/lysosomal (ML) fraction yields two distinct classes of lysosomes: the large lysosomes or protein droplets and a heterogeneous broad band of smaller lysosomes. The protein droplets which are recovered as a well defined zone of high purity also sediment as a homogeneous band after equilibrium banding at a density of 1.235 g/ml in sucrose. The small lysosomes co-sediment with other subcellular organelles as a broad band, indicated by the distribution of various acid hydrolases, which exhibit subtle heterogeneity among these small lysosomes. The distribution of renin containing granules indicates that in size they represent a distinct subpopulation of small lysosomes. Further fractionation of small lysosomes by equilibrium banding separates two distinct populations at densities 1.20 (small light) and 1.235 g/ml (small dense). Comparison of lysosomal populations fractionated in these studies with the distribution of lysosomal acid hydrolases along the different segments of the nephron suggests that large and small dense lysosomes probably originate from the proximal tubule while the small light lysosomes may contain lysosomes from the distal tubule. Very small, lysosome-like organelles subfractionated from the 'microsomes' may constitute a mixture of small light lysosomes, lysosomal fragments and endocytic vesicles from a variety of cell types. Time course studies with 3H labelled Cd-thionein, following intravenous administration, suggests that uptake in the kidney cortex is very rapid and that catabolism takes place in two distinct phases: rapid breakdown starting in the endosome compartment and slower breakdown in lysosomes. From the association of labelled lysozyme (125I) and Cd-thionein (109Cd) it appears that all the different lysosomal populations identified are at some stage involved with uptake and catabolism of these two proteins.

The pig mesonephros. I. Enzyme histochemical observations on the segmentation of the nephron

Cryostat sections from the mesonephros of various pig embryos with a crown-rump-length of between 17 and 95 mm were used for light microscopical assays of acid hydrolases (acid phosphatase, beta-D-N-acetylglucosaminidase, beta-D-glucuronidase), oxidoreductases (succinic dehydrogenase, NADH- and NADPH-tetrazolium reductase) and adenosine triphosphatases (Mg2+- and Na+--K+-ATPase). Our main intention was to distinguish more accurately between the different parts of the pig's nephron, which is exceedingly long and coiled. The proximal tubule, that exhibits a high activity for acid phosphatase but none in beta-D-glucuronidase incubations, shows no subsegmentation apart from a stronger reaction of its initial segment that was apparent in three of our assays. In the distal tubule, a preattachment convolution, an attachment zone, and a postattachment coil can be discriminated by a synopsis of all histiograms. The beginning of the collecting tubule is situated in the middle of the organ and not at its dorsal face as was previously believed. Up to three different segments can be discriminated in the collecting tubule. The distal and the collecting tubule harbor on ouabain-sensitive Na+--K+-ATPase activity which decreases considerably towards the Wolffian duct. The enzymatic maturation of the mesonephric pig nephron is almost completed in 17 mm embryos.

Steroid hormone binding receptors in the rat kidney

The studies were done on 93 Wistar rats of both sexes. Binding capacity and affinity for 3H-estradiol were determined biochemically in the cytosol fraction of renal homogenates. Free cytoplasmic estrogen binding sites were demonstrated in a portion of the females (Kd 5.2-17.8 x 10(-10) mol/l): in 33.3% of normal animals, in 54.6% 3-4 days after ovariectomy, and in 25% 17-18 days after ovariectomy. The investigation of females which received estradiol or testosterone replacement after castration, as well as of uncastrated or castrated males, led to negative results. Thaw-mounted autoradiography was used to study the retention of radioactivity from 3H-estradiol or 3H-testosterone in normal and castrated animals and in animals which received corresponding hormone replacement after castration. In all animals, specific silver granules were found in the cytoplasm and nucleus of proximal tubules cells from the S1 and S2 segments of juxtamedullary nephrons, particularly in the females. Only a few silver granules were observed in the S segments; some cells in males were marked by a heavy nuclear accumulation of silver granules following the injection of 3H-testosterone. In the distal tubules, only isolated silver granules were found in some cells. Somewhat more radioactivity was found in the cytoplasm of the cells of the collecting ducts in the inner medullary zone.