摘要:

The present study reports the effect of a reduction in the Na+-transport rate on cell volume. A decrease in transport rate was achieved by inhibition of the basolateral Na7K+ pump with ouabain. Cultured A6 cell monolayers were short-circuited and exposed to ouabain at the basolateral surface. In one series of experiments, cells were impaled with microelectrodes to measure cell voltage, apical fractional resistance and thus derive membrane conductances. Another set, A6, served for cell height measurements. Ouabain decreased short-circuit current (Isc), which is an index of transepithelial Na+ transport: the reduction in transport rate varied from 26 to 79% within 10 min. Equivalent circuit analysis revealed a 20% decrease in apical membrane conductance (ga), whereas basolateral membrane conductance (gb) increased by 66%. A decrease in cell voltage (12 mV) together with drop in ga during ouabain may account for the reduction in Isc. The rise in gb is mainly due to a gain in Cl- conductance which increased from 114 to 613 μS/cm2, compatible with activation of Cl- channels. All of this occurs without a detectable change in cell height. We may conclude from these data that inhibition of Na+ exit by ouabain is quickly compensated by a decrease in apical Na+ entry and an increase in basolateral Cl- conductance. Constant cell volume during ouabain implies that the total cell solute is essentially unchanged.

ISSN:1420-4096    

DOI:10.1159/000173825

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

We studied the effect of a saline load on proximal tubular Na+, fluid and HCO-3 handling of control and uninephrectomized (UNx) rats. Glomerular filtration rate (GFR) was measured by inulin clearance, Na+ reabsorption in the proximal tubule by lithium clearance (CLi+), proximal tubule fluid reabsorption (Jv) by microperfusion with l4C inulin and proximal tubule HCO-3 reabsorption (JHCO-3) by estimating pH of perfusate and collected fluid in vitro under CO2 equilibrated oil by means of Sb microelectrodes. No significant differences were found between control and UNx animals in baseline values of urine flow, GFR, fractional water and sodium excretion and blood and urine pH and pCO2, showing that renal function was compensated 4 weeks after UNx. On the other hand, UNx rats showed a significant increase in proximal tubule Jv and JHCO-3. After extracellular fluid volume expansion (EFVE) by infusion of HCO-3 Ringer solution (0.1 ml/min) during 90-120 min, in both groups of animals hematocrit decreased by 15%, GFR remained unchanged and fractional Na+ and water excretion increased significantly. However, after EFVE Jv and JHCO-3 decreased significantly in control rats but were not modified in UNx animals. Fractional proximal Na+ reabsorption as measured by CLi+ decreased in control rats after EFVE and was not altered in UNx rats. After EFVE the fall in fractional distal Na+ reabsortion was significantly higher in control than in UNx rats. The present results provide evidence that after a saline load the impaired natriuretic response in UNx rats could be attributed to an alteration in proximal and distal tubular Na+ and HCO-3 handling. The data also showed a close correlation between proximal tubular function evaluated by CLi+ and by Jv.

ISSN:1420-4096    

DOI:10.1159/000173826

出版商:S. Karger AG    

年代:1994

数据来源: Karger

ISSN:1420-4096    

DOI:10.1159/000173827

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

In the rat remnant kidney hydrogen peroxide (H2O2) production is increased when compared to the normal kidney. The activities of the peroxisomal H2O2-producing oxidases, D-amino acid oxidase and acylcoenzyme A oxidase, and of the extraperoxisomal superoxide dismutase are decreased in renal homogenate. The peroxisomal L-α-hydroxyacid oxidase and L-lactate oxidase as well as the peroxisomal H2O2 scavenger catalase preserve their activity. The activity of the cytosolic scavenging system, glutathione peroxidase, is decreased by 40%. A starvation period of 48 h does not produce a measurable increase in H2O2 production in the normal nor in the remnant kidney. On visual inspection, peroxisomal morphology and distribution in the renal tubules are similar in the normal and remnant kidney tissue

ISSN:1420-4096    

DOI:10.1159/000173828

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The adenosine triphosphate (ATP) generating pathways of dog inner medullary collecting ducts (IMCD) were examined in vitro using suspensions of dog IMCD tubules incubated under aerobic and anaerobic conditions. Glucose is always the preferred substrate for this tissue, even if lactate can be oxidized under aerobic conditions. The metabolism of glucose proceeds largely towards lactate accumulation in the presence or absence of oxygen. Glycogen is also consumed and more markedly so during anoxia. The pentose shunt represents a minor pathway for glucose metabolism in this tissue. Under aerobic conditions, the net oxidation of glucose to CO2 contributes significantly to the cell energetics, mitochondrial and cytoplasmic mechanisms sharing equally the ATP synthesis. In the absence of oxygen, only the cytoplasmic routes of ATP synthesis are used, but the apparent ATP turnover is markedly reduced. A marked inhibition of the activity of the Na-K-ATPase during anoxia explains this observation. The utilization of glucose for osmolyte synthesis is a minor process and appears to be suppressed under anaerobic conditions. It is concluded that the ATP turnover is low in dog IMCD cells as compared with that of other nephron segments and is largely dependent upon glucose availability under aerobic or anaerobic conditions.

ISSN:1420-4096    

DOI:10.1159/000173829

出版商:S. Karger AG    

年代:1994

数据来源: Karger

摘要:

The nephrotoxicity of cyclosporin A (CSA) after chronic treatment is well known and includes in later stages tubular atrophy associated with interstitial fibrosis. In order to examine whether interstitial ñbrosis due to CSA treatment in vivo is related to a hyperproliferative activity of fibroblasts, the effects of CSA on the growth characteristics of cultured human skin fibroblasts (HUSF) were investigated at CSA concentrations ranging from 10 ng/ ml to 50 µg/ml. We found that CSA at concentrations higher than 7.5 µg/ml inhibited cell proliferation (p < 0.05 at concentrations above 5 µg/ml; n = 3) and cloning efficiency (p < 0.05 at concentrations above 5 µg/ml; n = 3) in a dose-dependent manner and caused a promotion of cell attachment at concentrations above lOµg/ml (p < 0.05; n = 4), but did not influence cell spreading. At lower concentrations CSA-treated HUSF did not differ in their growth characteristics from the corresponding controls. A 50% inhibition of proliferation was calculated by extrapolation for a CSA concentration of 70 µg/ml for HUSF. The inhibition of HUSF proliferation was reversible even at the highest CSA concentration of 50 µg/ml. Under the same experimental conditions, a 50% inhibition of proliferation was observed for Madin-Darby canine kidney (MDCK) cells to be 5.5 µg/ml, e.g. at a 15-fold lower CSA concentration. Moreover, CSA caused a dose-dependent and reversible cell elongation of HUSF and a significant increase in the average cell diameter from 19.2 ± 0.3µm (control; mean ± SEM, n = 4) to 22.2 ± 0.2 µm for 50 µg/ml CSA (mean ± SEM, n = 4) and in median cell volume from 4,21·± 160 fl (control; mean ± SEM, n = 4) to 7,020 ± 190 fl for 50 µg/ ml CSA (mean ± SEM; n = 4). These alterations described above were not correlated with a cytotoxic effect as checked by a fluorescent staining for cell vitality. Alterations in the organization of cytoskeletal components such as stress fibers, intermediate-sized filaments and microtubules directly due to CSA treatment were not observed. In contrast, the amount of fibronectin present on the cell surface was considerably increased by CSA. Although HUSF in culture do not respond to CSA treatment by an increased proliferative activity, they are much less affected by CSA than other cell types (i.e MDCK cells). Thus, the increase in cell diameter and cell volume, respectively, and the increased amounts of surface fibronectin might explain the development of interstitial fibrosis in the kidney of humans and animals after

ISSN:1420-4096    

DOI:10.1159/000173830

出版商:S. Karger AG    

年代:1994

数据来源: Karger

ISSN:1420-4096    

DOI:10.1159/000173831

出版商:S. Karger AG    

年代:1994

数据来源: Karger