Nature of urate transport in isolated rabbit proximal tubules

Unidirectional fluxes of [14C]-urate from bath to lumen and from lumen to bath were measured in isolated perfused rabbit proximal tubules. The absorption of urate from the perfusate was small in magnitude and relatively insensitive to alteration by luminal probenecid or D-glucose. By contrast, peritubular probenecid inhibited urate secretion from bath to lumen in all three segments. To estimate the facilitated component of urate secretion for each bath concentration of the anion, the passive component of urate influx (probenecid-resistant influx) was subtracted from the total influx of urate. Urate secretion was strongly dependent on concentration of urate in the bath, the relationship being sigmoidal in many S1 and S2 segments. The S0.5 values of 187,251, and 234 X 10(-6) M obtained from Hill plots of mean data from S1, S2, S3 segments, respectively, indicated that the secretory mechanism had a relatively uniform affinity for urate along the proximal tubule. Vmax values for urate secretion were 568,592, and 55 X 10(-15) mol . min-1 . mm-1 for the same segments. Kinetic analysis indicated that axial heterogeneity of urate secretion is probably due to differences in the relative densities of urate transporters of common affinity along the proximal tubule. We suggest that in intact rabbits with low plasma levels urinary urate is the product of glomerular filtration, passive reabsorption, and minimal proximal secretion. With elevation of plasma urate above endogenous levels, S1 and S2 segments secrete urate at an accelerated rate, possibly reflecting action of a transporter with allosteric features.

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Basis for heterogeneity of para-aminohippurate secretion in rabbit proximal tubules

AJP Renal Physiology ◽

10.1152/ajprenal.1981.240.5.f430 ◽

1981 ◽

Vol 240 (5) ◽

pp. F430-F436 ◽

Cited By ~ 5

Author(s):

A. Shimomura ◽

A. M. Chonko ◽

J. J. Grantham

Keyword(s):

Basolateral Membrane ◽

Proximal Tubules ◽

Rabbit Kidney ◽

Passive Component ◽

Maximal Rate ◽

Michaelis Constant ◽

Slope Analysis ◽

High Concentrations ◽

The Relationship ◽

Membrane Density

Para-aminohippurate (PAH) is secreted at different rates in S1, S2, and S3 segments of isolated perfused proximal tubules of rabbit kidney. To characterize PAH transport we determined the maximal rate of secretion (Vmax) and the apparent Michaelis constant (Km) for each segment by examining the relationship between bath concentration of PAH and net PAH secretion (Jb leads to lPAH) transposed for Lineweaver-Burk analysis. The passive component of secretion for all segments was estimated by slope analysis at relatively high concentrations of PAH, by the component of PAH secretion insensitive to inhibition by probenecid, and, additionally, in S2 segments, from PAH efflux from lumen to bath. Subtraction of the passive component from Jb leads to lPAH (probenecid method) gave Vmax values for S1, S2, and S3 segments of 1,097 +/- 336 (n = 6), 7,430 +/- 1,338 (n = 6), 1,647 +/+ 138 (n = 8) X 10(-15) mol.min-1.mm-1 (+/- SE) and apparent Km values of 139 +/– 37 (n = 6), 195 +/- 37 (n = 6), and 113 +/- 16 (n = 6) X 10(-6) M, respectively. Thus, Vmax for S2 greater than S3 congruent to S1, whereas apparent Km was not consistently different among the segments. On the basis of these results we suggest that axial heterogeneity of PAH secretion may reflect an increased basolateral membrane density of PAH transporters of common affinity in the S2 segment of the proximal tubule.

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Lactate absorption in Thamnophis proximal tubule: transport versus metabolism

AJP Renal Physiology ◽

10.1152/ajprenal.1980.238.3.f218 ◽

1980 ◽

Vol 238 (3) ◽

pp. F218-F228 ◽

Cited By ~ 1

Author(s):

P. H. Brand ◽

R. S. Stansbury

Keyword(s):

Proximal Tubule ◽

Lactate Concentration ◽

Flux Ratio ◽

Proximal Tubules ◽

Chemical Gradient ◽

Flow Rates ◽

Net Flux ◽

Unidirectional Fluxes ◽

Absorptive Flux

Proximal tubules from the kidney of Thamnophis (garter snake) were perfused in vitro and unidirectional fluxes of lactate measured using L(+)-[U-14C]lactate, (lactate concentration, 1 mM). The lumen-to-bath (absorptive) flux (Jlb lact) significantly exceeded the bath-to-lumen flux (backflux) (Jbl lact) in each of 12 tubules (seven distal proximal and five proximal proximal). The flux ratio (Jlb lact/Jbl lact) was approximately 3.00. At flow rates of 13-16 nl/min and lactate concentration of 1 mM the net flux was about 1.60 pmol . min-1 . mm-1 in both proximal proximal and distal proximal segments. Both fluxes were decreased by perfusion at 5 degrees C. To determin e the contribution of metabolism of lactate to its absorption, Jlb lact was measured at 25 degrees C in 10 distal proximal tubules during perfusion with [14C]lactate, lactate concentration, 1 mM, and with [methoxy-3H]inulin. In these experiments, the amount of 14C found in the bath was 93% of the amount of 14C absorbed from the lumen. Chromatography showed that all of the 14C found in the bath was [14C]lactate. These data establish that in Thamnophis proximal tubule lactate absorption occurs against an electro chemical gradient by transport of the intact lactate molecule without significant metabolism.

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Urate transport in the nephron

AJP Renal Physiology ◽

10.1152/ajprenal.1979.237.2.f85 ◽

1979 ◽

Vol 237 (2) ◽

pp. F85-F92 ◽

Cited By ~ 2

Author(s):

I. M. Weiner

Keyword(s):

Proximal Tubules ◽

Secretory Process ◽

Experimental Conditions ◽

Unresolved Question ◽

Urate Transport ◽

Pars Recta ◽

Bidirectional Transport ◽

Unidirectional Fluxes ◽

Urate Secretion

This paper summarizes the literature on the sties of urate transport, secretory and reabosrptive, in the nephron. In the animals studied thus far the bulk of urate transport occurs in the proximal tubules. Two patterns of transport have been uncovered. In one, urate is secreted and reabsorbed throughout the convoluted tubule (perhaps the pars recta as well). The direction of net transport depends on the kind of animal studied and in some instances on the experimental conditions. In the second pattern there is a strong secretory process in the pars recta, and net secretion of urate, when it occurs, is attributable to that segment. In some but not all animals it is clear that urate secretion in the proximal tubules occurs by a mechanism separate from that which secretes p-aminohippurate (PAH). One important unresolved question is: How general is the occurrence of separate secretory mechanisms for PAH and urate? Another unresolved question is: What are the magnitudes of the unidirectional fluxes of urate in the segments in which bidirectional transport occurs?

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Reduction of Potassium in Kidney Proximal Tubules to Aid in Electron Probe X-Ray Microanalysis of Calcium

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119193 ◽

1985 ◽

Vol 43 ◽

pp. 474-475

Author(s):

A. LeFurgey ◽

P. Ingram ◽

L.J. Mandel

Keyword(s):

Smooth Muscle ◽

Proximal Tubule ◽

Electron Probe ◽

Clinical Applications ◽

Proximal Tubules ◽

Rabbit Kidney ◽

Target Cells ◽

X Ray ◽

Freeze Dried

For quantitative determination of subcellular Ca distribution by electron probe x-ray microanalysis, decreasing (and/or eliminating) the K content of the cell maximizes the ability to accurately separate the overlapping K Kß and Ca Kα peaks in the x-ray spectra. For example, rubidium has been effectively substituted for potassium in smooth muscle cells, thus giving an improvement in calcium measurements. Ouabain, a cardiac glycoside widely used in experimental and clinical applications, inhibits Na-K ATPase at the cell membrane and thus alters the cytoplasmic ion (Na,K) content of target cells. In epithelial cells primarily involved in active transport, such as the proximal tubule of the rabbit kidney, ouabain rapidly (t1/2= 2 mins) causes a decrease2 in intracellular K, but does not change intracellular total or free Ca for up to 30 mins. In the present study we have taken advantage of this effect of ouabain to determine the mitochondrial and cytoplasmic Ca content in freeze-dried cryosections of kidney proximal tubule by electron probe x-ray microanalysis.

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Association of Urinary and Plasma Levels of Trimethylamine N-Oxide (TMAO) with Foods

Nutrients ◽

10.3390/nu13051426 ◽

2021 ◽

Vol 13 (5) ◽

pp. 1426

Author(s):

Mauro Lombardo ◽

Giovanni Aulisa ◽

Daniele Marcon ◽

Gianluca Rizzo ◽

Maria Grazia Tarsisano ◽

...

Keyword(s):

Gut Microbiota ◽

Fish Consumption ◽

Plasma Levels ◽

Cooking Methods ◽

Saltwater Fish ◽

Increased Risk ◽

Mediator Role ◽

Fish And Shellfish ◽

The Relationship

Introduction: Trimethylamine N-oxide (TMAO) may play a key mediator role in the relationship between the diet, gut microbiota and cardiovascular diseases, particularly in people with kidney failure. The aim of this review is to evaluate which foods have a greater influence on blood or urinary trimethylamine N-oxide (TMAO) levels. Methods: 391 language articles were screened, and 27 were analysed and summarized for this review, using the keywords “TMAO” AND “egg” OR “meat” OR “fish” OR “dairy” OR “vegetables” OR “fruit” OR “food” in December 2020. Results: A strong correlation between TMAO and fish consumption, mainly saltwater fish and shellfish, but not freshwater fish, has been demonstrated. Associations of the consumption of eggs, dairy and meat with TMAO are less clear and may depend on other factors such as microbiota or cooking methods. Plant-based foods do not seem to influence TMAO but have been less investigated. Discussion: Consumption of saltwater fish, dark meat fish and shellfish seems to be associated with an increase in urine or plasma TMAO values. Further studies are needed to understand the relationship between increased risk of cardiovascular disease and plasma levels of TMAO due to fish consumption. Interventions coupled with long-term dietary patterns targeting the gut microbiota seem promising.

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Endocannabinoid reactivity to acute stress: Investigation of the relationship between salivary and plasma levels

Biological Psychology ◽

10.1016/j.biopsycho.2021.108022 ◽

2021 ◽

Vol 159 ◽

pp. 108022

Author(s):

Luke Ney ◽

Caleb Stone ◽

David Nichols ◽

Kim Felmingham ◽

Raimondo Bruno ◽

...

Keyword(s):

Plasma Levels ◽

Acute Stress ◽

The Relationship

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Plasma and cerebrospinal fluid inflammation and the blood-brain barrier in older surgical patients: the Role of Inflammation after Surgery for Elders (RISE) study

Journal of Neuroinflammation ◽

10.1186/s12974-021-02145-8 ◽

2021 ◽

Vol 18 (1) ◽

Author(s):

Sarinnapha M. Vasunilashorn ◽

◽

Long H. Ngo ◽

Simon T. Dillon ◽

Tamara G. Fong ◽

...

Keyword(s):

Cerebrospinal Fluid ◽

Blood Brain Barrier ◽

Plasma Levels ◽

Inflammatory Markers ◽

Brain Barrier ◽

Markers Of Inflammation ◽

Blood Brain ◽

Csf Levels ◽

The Relationship

Abstract Background Our understanding of the relationship between plasma and cerebrospinal fluid (CSF) remains limited, which poses an obstacle to the identification of blood-based markers of neuroinflammatory disorders. To better understand the relationship between peripheral and central nervous system (CNS) markers of inflammation before and after surgery, we aimed to examine whether surgery compromises the blood-brain barrier (BBB), evaluate postoperative changes in inflammatory markers, and assess the correlations between plasma and CSF levels of inflammation. Methods We examined the Role of Inflammation after Surgery for Elders (RISE) study of adults aged ≥ 65 who underwent elective hip or knee surgery under spinal anesthesia who had plasma and CSF samples collected at baseline and postoperative 1 month (PO1MO) (n = 29). Plasma and CSF levels of three inflammatory markers previously identified as increasing after surgery were measured using enzyme-linked immunosorbent assay: interleukin-6 (IL-6), C-reactive protein (CRP), and chitinase 3-like protein (also known as YKL-40). The integrity of the BBB was computed as the ratio of CSF/plasma albumin levels (Qalb). Mean Qalb and levels of inflammation were compared between baseline and PO1MO. Spearman correlation coefficients were used to determine the correlation between biofluids. Results Mean Qalb did not change between baseline and PO1MO. Mean plasma and CSF levels of CRP and plasma levels of YKL-40 and IL-6 were higher on PO1MO relative to baseline, with a disproportionally higher increase in CRP CSF levels relative to plasma levels (CRP tripled in CSF vs. increased 10% in plasma). Significant plasma-CSF correlations for CRP (baseline r = 0.70 and PO1MO r = 0.89, p < .01 for both) and IL-6 (PO1MO r = 0.48, p < .01) were observed, with higher correlations on PO1MO compared with baseline. Conclusions In this elective surgical sample of older adults, BBB integrity was similar between baseline and PO1MO, plasma-CSF correlations were observed for CRP and IL-6, plasma levels of all three markers (CRP, IL-6, and YKL-40) increased from PREOP to PO1MO, and CSF levels of only CRP increased between the two time points. Our identification of potential promising plasma markers of inflammation in the CNS may facilitate the early identification of patients at greatest risk for neuroinflammation and its associated adverse cognitive outcomes.

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Proximal tubule dysfunction in cystine-loaded tubules: effect of phosphate and metabolic substrates

AJP Renal Physiology ◽

10.1152/ajprenal.1996.271.3.f717 ◽

1996 ◽

Vol 271 (3) ◽

pp. F717-F722

Author(s):

G. Bajaj ◽

M. Baum

Keyword(s):

Oxygen Consumption ◽

Proximal Tubule ◽

Tricarboxylic Acid Cycle ◽

Dimethyl Ester ◽

Proximal Tubules ◽

Intracellular Atp ◽

Metabolic Substrates ◽

Rate Of Oxygen Consumption ◽

Intracellular Phosphate

Intracellular cystine loading by use of cystine dimethyl ester (CDME) results in a generalized inhibition in proximal tubule transport due, in part, to a decrease in intracellular ATP. The present study examined the importance of phosphate and metabolic substrates in the proximal tubule dysfunction produced by cystine loading. Proximal tubule intracellular phosphorus was 1.8 +/- 0.1 in control tubules and 1.1 +/- 0.1 nmol/mg protein in proximal tubules incubated in vitro with CDME P < 0.001). Infusion of sodium phosphate in rabbits and subsequent incubation of proximal tubules with a high-phosphate medium attenuated the decrease in proximal tubule respiration and prevented the decrease in intracellular ATP with cystine loading. Tricarboxylic acid cycle intermediates have been shown to preserve oxidative metabolism in phosphate-depleted proximal tubules. In proximal tubules incubated with either 1 mM valerate or butyrate, there was a 42 and 34% reduction (both P < 0.05) in the rate of oxygen consumption with cystine loading. However, tubules incubated with 1 mM succinate or citrate had only a 13 and 14% P = NS) reduction in the rate of oxygen consumption, respectively. These data are consistent with a limitation of intracellular phosphate in the pathogenesis of the proximal tubule dysfunction with cystine loading.

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