摘要:

Double-barrel microelectrodes were used to determine membrane voltages and the intracellular pH (pHi) in primary cultures of cortical collecting duct cells (CCD) grown in the absence of aldosterone. Electrophysiologically, two main cell types were identified. In cell type 1, the apical membrane voltage (Va) was -60 ± 5 mV. The fractional resistance of the apical membrane (fRa) was 0.40 ± 0.03, and pHi was 7.21 ± 0.04. Exposure to 50 mM K+ on the apical side depolarized Va by 21 ± 4 mV. When Cl- was replaced by cyclamate two types of responses were observed: (a) depolarization of Va by 26 ± 3 mV while pHi remained unchanged, and (b) no change in Va. In cell type 2, Va was -36 ± 5 mV, fRa was 0.91 ± 0.03 and increasing apical [K+] from 5 to 50 mM did not change Va. Two subpopulations were distinguished by the response of pHi to lowering apical [Cl-]. In one of them pHi increased from 6.99 ± 0.05 to 7.11 ± 0.07. In the other, pHi was significantly decreased from 7.16 ± 0.08 to 7.03 ± 0.07. These results are compatible with the conclusion that about 50% of the impaled cells type 2 have a Cl-/HCO-3 exchanger at the apical membrane. In summary, two different cell types can be identified electrophysiologically in CCD monolayers. Cell type 1 has the electrical characteristics of principal cells. Cell type 2 resembles the intercalated cells. The cell alkalinization observed in approximately 50% of the cells type 2 in response to Cl- removal suggests the presence of an apical Cl-/HCO-3 exchanger. Thus, these cells should be the bicarbonate-secreting cells. The remaining cells should correspond to the acid-secre

ISSN:1420-4096    

DOI:10.1159/000173382

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Glomerular mesangial cells require Cl ions for the development of a variety of metabolic and functional properties. In the present study the electrochemical distribution for Cl- was examined in cultured rat mesangial cells with Cl--sensitive intracellular microelectrodes. It was determined that the intracellular Cl activity exceeded the levels predicted for a passively distributed ion. This was further substantiated by exposing mesangial cells to 10-5M bumetanide which drove intracellular Cl to a value close to electrochemical equilibrium. We conclude that Cl accumulates in mesangial cells, against its electrochemical gradient, through a transport pathway that is highly sensitive to bumetanide.

ISSN:1420-4096    

DOI:10.1159/000173383

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Side-specific expression and activity of Na:K pump was studied in Madin-Darby canine kidney (MDCK) cells, a tissue culture model of distal renal tubular epithelium, exposed to low ambient potassium. Confluent monolayers grown on teflon filters in dual chambers were treated with a low K+ medium from 45 min to 72 h. After both acute (45 min) and longer-term (24-72 h) exposure to low K+ (0.7 mM), cation cycling rate of existing pump units increased substantially, while there was no significant change in total cell Na-K-ATPase activity or in basolateral surface pump density. Although a small quantity of Na:K pumps ( < 10%) was consistently present apically, it also did not increase after exposure to low K+ or when the monolayers were provided K+ only from the apical side. In MDCK monolayers low K+ enhances the rate of K+ uptake by the existing pump units but does not increase the total number of pumps or their deployment on either cell surface.

ISSN:1420-4096    

DOI:10.1159/000173384

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The addition of substrate in the form of lactate (L), but not glucose (G), increases the respiration of canine thick ascending limb (TAL) segments in a saturable (above 2 mM) fashion. More than 60% of this stimulation is ouabain-sensitive (1 mM ouabain) even if L and G transport are both sodium-insensitive processes in TAL. Thus L, but not G, specifically stimulates Na+ entry in TAL cells and its subsequent transport by the Na+, K+-ATPase. If chloride is substituted for by gluconate, no significant substrate-induced stimulation of ouabain-sensitive respiration is observed. SITS (4-acetamino-4’-isothiocyanostilbene-2,2’-disulfonic acid) also interferes with the L-induced stimulation of respiration. Thus L entry in TAL appears to be directly or indirectly coupled to the transepithelial flux of Cl-. Furosemide (F) but not amiloride, also inhibits this stimulation suggesting that the accelerated Na+ entry triggered by the application of L occurs through the F-sensitive carrier or that lactate transport is F-sensitive in TAL cells. In accord, F specifically impairs the metabolism of L (as compared to G). These data suggest that in intact TAL tubules both lactate uptake and oxidation are directly or indirectly influenced by the transcellular flux of NaCl. This organization may participate to maintain a stoichiometry between the transport of NaCl and the availability of L to support the energetic needs of TAL ce

ISSN:1420-4096    

DOI:10.1159/000173385

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Hippurate action on glucose utilization was evaluated in rat kidney cortex slices. Studies have shown the following. (1) Hippurate inhibits markedly basal as well as insulin-stimulated glucose utilization and basal gluconeogenesis. (2) Ca deficiency and specific Ca channel blockers diltiazem and isradipine abolish the hippurate inhibition of glucose utilization. (3) K+ channel blockers, i.e. the increased K+ concentration in incubation medium, procaine and sulfonylurea drugs also abolish the hippurate inhibition of glucose utilization. It is concluded that hippurate and benzoate operate through the ATP-dependent K+ channel.

ISSN:1420-4096    

DOI:10.1159/000173386

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The anticancer drug adriamycin (ADR) is selectively toxic to glomerular cells when administered intravenously (5 mg/kg b.w.) to female MWF/Ztm rats. Recent data have shown that the proteinuria associated with the lesion does not occur in cortical glomeruli, suggesting the selective injury of juxtamedullary glomeruli. In the present study, the effect of ADR on glomerular metabolism was studied with special reference to possible differences between cortical and juxtamedullary glomeruli. On day 7 after ADR treatment, cortical and juxtamedullary glomeruli were separately isolated by the sieving method and 14C glucose oxidation to 14C02 and the incorporation of 3H proline into macromolecules were measured in vitro and used to study target selective injury in ADR-treated rats compared to control rats. The investigations revealed differences in the response of cortical and juxtamedullary glomeruli to ADR. ADR treatment increased proline incorporation over a 4-hour incubation period in both glomerular populations compared to controls, but the effect was significantly (p < 0.05) more pronounced in juxtamedullary glomeruli (juxtamedullary: 187 ± 8% of control; cortical: 167 ± 4% of control). Glucose oxidation was enhanced after 4 h only in juxtamedullary glomeruli (juxtamedullary: 132 ± 3% of control; cortical: 82 ± 10% of control). These data show that glomerular damage caused by ADR is associated with a stimulating effect on glomerular metabolism which is more marked in juxtamedullary than in cortical glomeruli, thus indicating a heterogenous response of different glomerular populations and supporting the concept that the selective damage of juxtamedullary glomeruli accounts for the proteinu

ISSN:1420-4096    

DOI:10.1159/000173387

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Three ultrastructural cytochemical methods have been used to classify the innervation of the rat renal cortex. Every axon seen contained chromaffin-reactive, dense core vesicles and stained for tyrosine hydroxylase, indicating that they were all catecholaminergic. About 10% of the axons associated with smooth muscle and juxtaglomerular cells of the arteriolar vessels also contained dopa decarboxylase, but this enzyme was not present in any of the peritubular axons. Our results are compatible with the possibility that, in the rat, the juxtaglomerular blood vessels, but not the renal tubules, are supplied by dopaminergic as well as by noradrenergic nerves.

ISSN:1420-4096    

DOI:10.1159/000173388

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

Tubular function was measured by lithium clearance (CLi) and by its derived formulae before and after the transient increase (lasting 90min) in glomerular filtration rate (GFR) following a meat meal (2g protein/kg body weight) in 12 normal children. Three baseline and 4 clearances after the meal were obtained, each lasting 30min. The mean baseline CLi was 23.1 ± 1.64ml/min/1.73m2. At peak GFR response (60min from starting the meal), CLi averaged 27.6 ± 2.4ml/min/1.73m2 (p < 0.025vs. baseline) and it was further increased (32.2 ± 5.04ml/ min/1.73m2, p < 0.01 vs. baseline) 120min after starting the meal, while GFR returned to baseline values. Fractional lithium excretion averaged 0.23 ± 0.04 at baseline and increased continuously after the meat meal and, at completion of the study, it averaged 0.38 ± 0.07 (p < 0.025vs. baseline). The distal absolute and fractional sodium reabsorption increased throughout the studies following the meal and peaked at 120 min. The functional changes were associated with a statistically significant increase in the plasma concentration of insulin, glucagon, and total amino acids after the meal. The latter at the end of the study was almost doubled (5,600 ± 780 versus 3,200 µM at baseline, p < 0.01). The data indicate that the tubulo glomerular feedback mechanism operates normally after a meat meal. The finding on increased distal sodium reabsorption might point to the existence of an insulin-dependent mec

ISSN:1420-4096    

DOI:10.1159/000173389

出版商:S. Karger AG    

年代:1991

数据来源: Karger

摘要:

The influence of food and water intake on renal function was assessed by comparisons between the hyperphagic Zucker obese rat and its lean littermate, which demonstrates nocturnal dominance in activity. Serum creatinine and cortisol levels, creatine kinase activities, creatinine and urine clearances, and sodium and potassium excretion rates were measured over a 24-hour period in both lean and obese rats (n = 24 each). Six rats in each group were studied every 8 h to permit characterization over a 12-hour light/dark cycle at 2-hour intervals. Urine and creatinine clearances were increased in lean rats during the dark phase coincident with onset of eating. Similarly, renal sodium and potassium excretion rates were markedly increased during the dark cycle, despite relatively constant serum potassium and sodium levels over the 24-hour period. In contrast, no circadian patterns in urine and creatinine clearances were found in the obese rat, which exhibits continuous feeding habits throughout the 24-hour period. Moreover, renal electrolyte excretion in the obese rat was modestly increased during the dark cycle, unlike the significant differences over time observed in lean rats. Serum creatinine levels were increased during the dark cycle in both rat groups. Creatine kinase activity, a measure of ambulatory activity, was constant in lean rats during the study period. Although creatine kinase activity was increased in obese rats during the dark cycle, no correlations with renal functional parameters were found. These results indicate that differences in food and water intake are significant determinants in diurnal cyclic changes in renal function.

ISSN:1420-4096    

DOI:10.1159/000173390

出版商:S. Karger AG    

年代:1991

数据来源: Karger