摘要:

The established opossum kidney (OK) cell line serves as a model system for ion and substrate transport in the renal proximal tubule. Previous experiments on OK cells revealed a channel-mediated Na+ conductance which is regulated by intracellular pH (pHi). In this study we report on patch clamp experiments determining the properties and pHi dependence of a cation channel located in the apical membrane. This channel is selective for sodium over chloride but discriminates poorly between the monovalent cations Na+, K+, Li+ and Cs+. Its open probability (Po) rises at depolarising membrane potentials. Under normal conditions the channel is inactive in the cell-attached patch mode and is activated upon excision. However, after excision the channel usually runs down within 30-90 s which cannot be overcome by either altering the Ca2+-concentration (10-3mol/l, 10-6mol/l, Ca2+-free) or adding 1 mmol/l Mg-ATP to the bath solution. In the cell-attached patch mode the channel could be activated by decreasing pHi from pH 7.4 to pH 6.5, by either the ammonium prepulse technique or the nigericin K+ method, in more than 50% of the experiments performed. In the renal proximal tubule such a non-selective cation channel would constitute a functional Na+ channel and might therefore support Na+ reabsorption especially during the intracellular acidification due to hormonal inhibition of the Na+/H+ exchanger.

ISSN:1420-4096    

DOI:10.1159/000173913

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Renal clearance, microperfusion and patch-clamp techniques were used to investigate the effects of the K-channel blocker glyburide on electrolyte excretion, the transport properties of the thick ascending limb (TAL) of Henle and K-channel activity in the apical membrane of the TAL and of the cortical collecting tubule. Our data suggest that the K-channel blocker glyburide can inhibit transport of Na and K in the TAL by blocking K recycling across the apical membrane. Additionally, inhibition of K secretion in the collecting ducts occurs by decreasing the activity of apical K channels and prevents kaliuresis.

ISSN:1420-4096    

DOI:10.1159/000173914

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

We have previously shown that smooth muscle contains three types of myosin heavy chains: SM1, SM2, and SMemb. The present study was designed to assess how glomerular expression of mRNA for these isoforms is regulated and whether their expression is affected by enalapril treatment in diabetic rats. Animals were divided into 4 groups: (1) untreated diabetic rats; (2) enalapril-treated diabetic rats; (3) untreated control rats, and (4) enalapril-treated control rats. Enalapril treatment was continued for 24 weeks. The glomerular mRNA levels for SM1 and SM2 showed little change in all groups throughout the experimental period. In contrast, SMemb mRNA in group 1 increased significantly with age compared to levels found in untreated controls (4.6-fold higher at 4 weeks, p < 0.01; 6.8-fold higher at 12 weeks, p < 0.01, and 10.6-fold higher at 24 weeks, p < 0.001). Enalapril reduced both creatinine clearance (p < 0.01) and urinary protein excretion (p < 0.01) in diabetic rats. Moreover, enalapril significantly attenuated the increase in the glomerular SMemb mRNA level in diabetic rats (the difference between treated and untreated rats was significant at p < 0.01 from week 4 to 24). However, enalapril had no effect on SMemb mRNA levels in controls. These data suggest that SMemb is a molecular marker for phenotypic alteration and that the beneficial effect of enalapril on proteinuria and renal function may be, at least in part, associated with reducing SMemb mRNA expression in diabetic glomeruli.

ISSN:1420-4096    

DOI:10.1159/000173915

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

We investigated the last step of mercapturic acid formation, the N-acetylation of cysteine S-conjugates, in the established opossum kidney (OK) cell line which exhibits characteristics of the proximal tubule. S-Benzyl-L-cysteine was used as a model substance for such a cysteine S-conjugate. We succeeded in showing that OK cells absorb S-benzyl-L-cysteine via an active transport system which is inhibitable by phenylalanine. This transport follows Michaelis-Menten kinetics and the two characterizing parameters were determined: the Michaelis-Menten constant Km = 1.8mmol/l, and the maximum of the difference between the intracellular and the extracellular concentration of S-benzyl-L-cysteine △cmax = 19.4 mmol/l. S-Benzyl-L-cysteine is converted to N-acetyl-S-benzyl-L-cysteine at a constant rate, which is independent of the extracellular S-benzyl-L-cysteine concentration. Under the tested experimental conditions this is probably due to saturation of the microsomal N-acetyltransferase catalyzing this reaction. In conclusion, we have shown that OK cells are a suitable model for studying mercapturate formation. They take up S-benzyl-L-cysteine mainly via the same carrier as phenylalanine, which is known to be transported in the rat by the high-capacity, low-affinity neutral amino acid carrier, and convert it to N-acetyl-L-benzyl-S-cystein

ISSN:1420-4096    

DOI:10.1159/000173916

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The role of nitric oxide (NO) synthesis in the peripheral vasodilation and sodium retention that occurs after partial portal vein ligation (PVL) was investigated. Hemodynamic studies in PVL rats with sodium retention and in sham-operated controls were conducted on the day when PVL rats developed transient and maximal sodium retention. Measurements were obtained before and during two consecutive periods after NO synthesis inhibition with NG-monomethyl-L-arginine (L-NMMA). Under baseline conditions, PVL rats with sodium retention were hypotensive, with equivalent decreases in total peripheral resistance and glomerular filtration rate in comparison to the control group. After L-NMMA, peripheral resistance and arterial pressure increased by similar extent in both groups. As compared with controls, PVL rats with sodium retention remained hypotensive and vasodilated. Furthermore, L-NMMA-induced natriuresis was attenuated in the PVL group. Additionally, serum and urinary levels of nitrate and nitrite did not vary before surgery and at the time of sodium retention. These results suggest that in PVL rats (1) vasodilation is not NO mediated; (2) vasodilation is not a sufficient explanation for sodium retention, and (3) a sodium-retaining factor acting on the renal tubules is responsible for sodium retention.

ISSN:1420-4096    

DOI:10.1159/000173917

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The tubular effects of furosemide were studied by micropuncture and clearance techniques on 20 rats. Collections of tubular fluid (TF) from early distal (ED) and late proximal (LP) segments of the same nephrons and of different nephrons were performed during baseline conditions. Re-collections were taken from the same sites and new collections from different nephrons after 10 mg/kg furosemide. The glomerular filtration rate (GFR) was 1,309 ± 212µl/min during baseline, and 1,348 ± 199 µl/min after furosemide (p > 0.89); while the urine flow rate rose from 36 ± 8 to 167 ± 30µl/min (p 0.63). In 31 paired ED-LP collections, PR was 82+4 (ED) versus 72 ± 4% (LP) during baseline, and 87 ± 3 versus 74 ± 6%, respectively, during furosemide. The respective collection rates were 4.6 ± 1.0 versus 9.5 ± 1.3 nl/min during baseline (p < 0.0001), 5.8 ± 2.3 versus 8.7 ± 3.0 nl/min during furosemide. The LP-ED differences obtained during baseline were not different from those measured during furosemide for the collection rate, PR and NFRs. The absolute LP resorption rate was not significantly different during baseline as compared to furosemide. Thus, furosemide did not affect the difference between ED and LP collection sites in collection rate, absolute and fractional reabsorption, in the absence of changes in GFR and NFR. These data indicate that furosemide acts solely along Henle’s loop, where it blocks Na+ transport. The urine flow rate rises during furosemide because water abstraction along the distal tubule is reduced by the isotonicity of ED TF, and along the collecting ducts by the isotonicity of the medullary and papillary interstitium caused by the diuretic. We conclude that under the conditions of the present study, furosemide

ISSN:1420-4096    

DOI:10.1159/000173918

出版商:S. Karger AG    

年代:1995

数据来源: Karger