In colchicine-treated rats, cellular distribution of AQP-1 in convoluted and straight proximal tubule segments is differently affected

We examined the effect of a high-salt (HS) diet on the regulation of renal cortical Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) in young Dahl salt-sensitive (DS) and salt-resistant (DR) rats. The activity of Na(+)-K(+)-ATPase, determined in permeabilized proximal tubule segments, was similar in DS and DR rats on normal salt (NS) diet. HS diet resulted in a twofold increase in proximal tubule Na(+)-K(+)-ATPase activity in DS rats but not in DR rats. The mRNA abundance, which was also similar in DS and DR rats on NS diet, increased after 2 days on HS diet in both innervated and denervated kidneys from DS rats but had no effect in DR rats. The activity of Na(+)-K(+)-ATPase and the content of alpha 1- and beta-protein in cortical homogenate were similar in DS and DR rats on both NS and HS diets. Treatment with benserazide, an inhibitor of dopa decarboxylase, upregulated proximal tubule Na(+)-K(+)-ATPase activity and increased Na(+)-K(+)-ATPase mRNA in DR rats on HS diet. Taken together, these data indicate that there is a primary defect in the dynamic hormonal regulation of Na(+)-K(+)-ATPase activity in intact tubular cells, which might stimulate Na(+)-K(+)-ATPase transcription.

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Ammonia production and secretion by S3 proximal tubule segments from acidotic mice: role of ANG II

AJP Renal Physiology ◽

10.1152/ajprenal.00189.2003 ◽

2004 ◽

Vol 287 (4) ◽

pp. F707-F712 ◽

Cited By ~ 21

Author(s):

Glenn T. Nagami

Keyword(s):

Proximal Tubule ◽

Ang Ii ◽

Ammonia Production ◽

Low Sodium ◽

Luminal Perfusion ◽

And Control ◽

Acid Loading ◽

Proximal Tubule Segments ◽

Secretion Rates

ANG II has potent effects on ammonia production and secretion rates by the proximal tubule and is found in substantial concentrations in the lumen of the proximal tubule in vivo. Because our previous studies demonstrated that acid loading enhanced the stimulatory effects of ANG II on ammonia production and secretion by S2 proximal tubule segments, we examined the effect of ANG II on ammonia production and secretion by isolated, perfused S3 segments from nonacidotic control mice and acidotic mice given NH4Cl for 7 days. In the absence of ANG II, ammonia production and secretion rates were no different in S3 segments from acidotic and control mice. By contrast, when ANG II was present in the luminal perfusion solution, ammonia production and secretion rates were stimulated, in a losartan-inhibitable manner, to a greater extent in S3 segments from acidotic mice. Ammonia secretion rates in S3 segments were largely inhibited by perfusion with a low-sodium solution containing amiloride in the presence or absence of ANG II. These results demonstrated that isolated, perfused mouse S3 proximal tubule segments produce and secrete ammonia, that NH4Cl-induced acidosis does not affect the basal rates of ammonia production and secretion, and that ANG II, added to the luminal fluid, stimulates ammonia production and secretion to a greater extent in S3 segments from acidotic mice. These findings suggest that S3 segments, in the presence of ANG II, can contribute to the enhanced renal excretion that occurs with acid loading.

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Peritubular transport of ochratoxin A by single rabbit renal proximal tubules.

Journal of the American Society of Nephrology ◽

10.1681/asn.v9111973 ◽

1998 ◽

Vol 9 (11) ◽

pp. 1973-1982 ◽

Cited By ~ 1

Author(s):

J R Welborn ◽

C E Groves ◽

S H Wright

Keyword(s):

Proximal Tubule ◽

Ochratoxin A ◽

Organic Anion ◽

High Capacity ◽

Organic Anion Transporter ◽

Epifluorescence Microscopy ◽

Proximal Tubule Cells ◽

Anion Transporter ◽

Uptake Medium ◽

Proximal Tubule Segments

Epifluorescence microscopy was used to study peritubular transport of the fluorescent mycotoxin ochratoxin A (OTA) into single proximal tubule segments of the rabbit. Initial rates of OTA uptake into S2 segments were saturable and adequately described by Michaelis-Menten kinetics, with an apparent Km of 2.2+/-0.3 microM (SEM). Several lines of evidence indicated that peritubular uptake of OTA in S2 segments was effectively limited to the "classical" organic anion transporter. First, 5 mM p-aminohippurate (PAH) cis-inhibited the uptake of 1 microM OTA into tubules by 96%. Kinetic analysis of the inhibition of OTA uptake by PAH (100 microM to 5 mM) yielded an apparent Ki of 164 microM, similar to the 100 to 200 microM range of Km values previously reported for the peritubular uptake of PAH. Second, efflux of OTA from tubules was trans-stimulated 3.2-fold by the presence of 2.5 mM PAH in the uptake medium. Third, 100 microM alpha-ketoglutarate (alphaKG) trans-stimulated the uptake rate of 1 microM OTA by 1.8-fold. Fourth, besides PAH, other organic anions effectively cis-inhibited the uptake of 1 microM OTA into tubules (inhibitor, % inhibition): 1.5 mM alphaKG, 80%; 1 mM probenecid, 100%; 1 mM piroxicam, 100%; 1 mM octanoate, 100%. In contrast, 1.5 mM tetraethylammonium, an organic cation, blocked uptake of 1 microM OTA by only 7%. The inhibition of OTA uptake into S1 and S3 segments of the proximal tubule was qualitatively similar: 5 mM PAH cis-inhibited the uptake of 1 microM OTA by approximately 95% in both S1 and S3 segments. Thus, peritubular OTA uptake into all segments of the proximal tubule appears to be dominated by its interaction with the classical organic anion transporter. The high-affinity and relatively high capacity of this pathway for OTA suggest that peritubular uptake may be a significant avenue for the entry of this toxin into proximal tubule cells.

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Regulation of renal NaDC1 expression and citrate excretion by NBCe1-A

AJP Renal Physiology ◽

10.1152/ajprenal.00015.2019 ◽

2019 ◽

Vol 317 (2) ◽

pp. F489-F501 ◽

Cited By ~ 3

Author(s):

Gunars Osis ◽

Kierstin L. Webster ◽

Autumn N. Harris ◽

Hyun-Wook Lee ◽

Chao Chen ◽

...

Keyword(s):

Metabolic Acidosis ◽

Proximal Tubule ◽

Wild Type ◽

Outer Medulla ◽

Extracellular Signals ◽

Citrate Metabolism ◽

Acid Loading ◽

Convoluted Tubules ◽

Proximal Tubule Segments

Citrate is critical for acid-base homeostasis and to prevent calcium nephrolithiasis. Both metabolic acidosis and hypokalemia decrease citrate excretion and increase expression of Na+-dicarboxylate cotransporter 1 (NaDC1; SLC13A2), the primary protein involved in citrate reabsorption. However, the mechanisms transducing extracellular signals and mediating these responses are incompletely understood. The purpose of the present study was to determine the role of the Na+-coupled electrogenic bicarbonate cotransporter (NBCe1) A variant (NBCe1-A) in citrate metabolism under basal conditions and in response to acid loading and hypokalemia. NBCe1-A deletion increased citrate excretion and decreased NaDC1 expression in the proximal convoluted tubules (PCT) and proximal straight tubules (PST) in the medullary ray (PST-MR) but not in the PST in the outer medulla (PST-OM). Acid loading wild-type (WT) mice decreased citrate excretion. NaDC1 expression increased only in the PCT and PST-MR and not in the PST-MR. In NBCe1-A knockout (KO) mice, the acid loading change in citrate excretion was unaffected, changes in PCT NaDC1 expression were blocked, and there was an adaptive increase in PST-MR. Hypokalemia in WT mice decreased citrate excretion; NaDC1 expression increased only in the PCT and PST-MR. NBCe1-A KO blocked both the citrate and NaDC1 changes. We conclude that 1) adaptive changes in NaDC1 expression in response to metabolic acidosis and hypokalemia occur specifically in the PCT and PST-MR, i.e., in cortical proximal tubule segments; 2) NBCe1-A is necessary for normal basal, metabolic acidosis and hypokalemia-stimulated citrate metabolism and does so by regulating NaDC1 expression in cortical proximal tubule segments; and 3) adaptive increases in PST-OM NaDC1 expression occur in NBCe1-A KO mice in response to acid loading that do not occur in WT mice.

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Expression of calcineurin activity and alpha-subunit isoforms in specific segments of the rat nephron

AJP Renal Physiology ◽

10.1152/ajprenal.1995.269.4.f558 ◽

1995 ◽

Vol 269 (4) ◽

pp. F558-F563 ◽

Cited By ~ 6

Author(s):

J. A. Tumlin ◽

J. T. Someren ◽

C. E. Swanson ◽

J. P. Lea

Keyword(s):

Atpase Activity ◽

Proximal Tubule ◽

Proximal Tubules ◽

Alpha Subunit ◽

Specific Substrate ◽

Fk 506 ◽

Collecting Ducts ◽

Subunit Isoforms ◽

Proximal Tubule Segments ◽

Calcineurin Activity

Calcineurin activity and alpha-subunit expression were studied in microdissected proximal tubules (S2), medullary thick ascending limbs (MTAL), cortical collecting ducts (CCD), connecting tubules (CNT), and outer medullary collecting ducts (OMCD). We have shown that cyclosporin A (CsA) and FK-506 inhibit sodium-potassium-adenosinetriphosphatase (Na-K-ATPase) activity in CCD, OMCD, and MTAL but did not uncover the mechanism for resistance of proximal tubule segments to these drugs. Because cells expressing high calcineurin activity are relatively resistant to the biological effects of CsA and FK-506, we hypothesized that the resistance of proximal tubules may be linked to increased calcineurin expression. Consequently, we measured calcineurin activity in microdissected tubules using a calcineurin-specific substrate. Calcineurin activity in S2 proximal tubule segments was 10-fold higher than in CCD, CNT, OMCD, or MTAL. FK-506 (6.0 ng/ml) inhibited calcineurin activity in CCD, CNT, and MTAL but not S2; 250 ng/ml FK-506 inhibited S2 calcineurin activity by 50%. Likewise, high concentrations of CsA (25 micrograms/ml) and FK-506 (250 ng/ml) inhibited S2 Na-K-ATPase activity by 77 and 73%, respectively. To investigate whether the resistance of S2 segments might be due to differential expression of calcineurin alpha-subunit isoforms, we determined the isoform expression by Western blot analysis using isoform-specific antibodies against the alpha 1-, alpha 2-, and alpha 3-isoforms. We found that alpha 1 expression in S2 was significantly greater than in the CCD and MTAL, whereas alpha 2 expression in the S2 was significantly less than in CCD and MTAL. No alpha 3 was detected in any nephron segment tested.(ABSTRACT TRUNCATED AT 250 WORDS)

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Seasonal and Morphological Variations of Brown Trout (Salmo truttaf.fario) Kidney Peroxisomes: A Stereological Study

Microscopy and Microanalysis ◽

10.1017/s1431927616011995 ◽

2016 ◽

Vol 22 (6) ◽

pp. 1146-1154

Author(s):

Albina D. Resende ◽

Alexandre Lobo-da-Cunha ◽

Fernanda Malhão ◽

Eduardo Rocha

Keyword(s):

Proximal Tubule ◽

Brown Trout ◽

Gonad Maturation ◽

Morphological Parameters ◽

Morphological Variations ◽

Variation Patterns ◽

Maturation Stages ◽

Males And Females ◽

First Time ◽

Proximal Tubule Segments

AbstractLiterature about fish kidney peroxisomes is scarce. To tackle this caveat, a stereological approach on renal peroxisome morphological parameters was performed for the first time in a fish, establishing correlations with maturation stages as it was previously done in brown trout liver. Three-year-old brown trout males and females were collected at the major seasons of their reproductive cycle. Trunk kidney was fixed and processed for catalase cytochemistry. Classical stereological methods were applied to electromicrographs to quantitate morphological parameters. Different seasonal variation patterns were observed between genders, and between renal proximal tubule segments I and II. In males, peroxisomes from proximal tubule segment II had a relatively higher volume and number in May, being individually bigger in February. Females presented similar trends, though with less marked variations. Overall, males and females did not show exactly the same seasonal patterns for most peroxisomal parameters, and no correlations were found between the latter and the gonado-somatic index (GSI). Hence, and despite the variations, the morphology of renal peroxisomes is not strictly correlated with gonad maturation kinetics, therefore suggesting that kidney peroxisome morphology is not seasonally modulated by sex steroids, like estradiol, as it seems to happen in liver peroxisomes.

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