Anion permeabilities of the isolated perfused rabbit proximal tubule

1982 ◽  
Vol 242 (4) ◽  
pp. F395-F405 ◽  
Author(s):  
D. G. Warnock ◽  
V. J. Yee
Keyword(s):  
Proximal Tubule ◽  
Sodium Transport ◽  
Permeability Coefficient ◽  
Negative Charge ◽  
Ion Selectivity ◽  
Proximal Tubules ◽  
Active Sodium ◽  
Chloride Permeability ◽  
Per Se ◽  
Two Populations

Electrophysiologic and isotopic techniques were used to characterize the anion permeabilities of isolated perfused rabbit proximal tubules (S2 segments). Tubules were differentiated into chloride- and sodium-selective populations by electrophysiologic rather than by anatomic criteria. The tubules were studied under conditions that inhibited active sodium transport. The isotopic chloride permeability coefficient was 5.5 +/- 0.6 X 10(-5) cm/s (n = 19) for chloride-selective tubules and 3.2 +/- 0.6 X 10(-5) cm/s (n = 15) for sodium-selective tubules. The isethionate permeability coefficient was 1.1 +/- 0.2 X 10(-5) cm/s (n = 23) and did not vary with sodium or chloride selectivity. The variation of oxyanion permeability (bicarbonate, isethionate, and cyclamate) relative to chloride resulted from changes in chloride permeability, per se, rather than any change in the oxyanion permeability. A consistent relation between bicarbonate and isethionate permeability permitted the permeability of bicarbonate ion to be estimated at 1.3 X 10(-5) cm/s. The mechanism of ion selectivity appears to be different for the two populations of tubules. Chloride-selective tubules appear to hve relatively small pathways that do not contain fixed-charge sites. In contrast, sodium-selective tubules may have permeation pathways that contain fixed negative-charge sites.

Interactions between gluconeogenesis and sodium transport in rabbit proximal tubule

1984 ◽  
Vol 246 (6) ◽  
pp. F859-F869 ◽  
Author(s):  
S. R. Gullans ◽  
P. C. Brazy ◽  
V. W. Dennis ◽  
L. J. Mandel
Keyword(s):  
Proximal Tubule ◽  
Sodium Transport ◽  
Acid Metabolism ◽  
Renal Proximal Tubule ◽  
Active Sodium ◽  
Atp Production ◽  
Cellular Energy ◽  
Glucose Synthesis ◽  
And Control ◽  
Gluconeogenic Substrate

Gluconeogenesis and sodium transport are ATP-requiring functions of the renal proximal tubule. Previously observed interactions between these processes indicated that they may compete for cellular energy. We have reevaluated this interaction in the rabbit proximal tubule using two preparations: suspensions of cortical tubules and isolated perfused tubules. In the presence of lactate and alanine, net glucose synthesis was 22.3 +/- 1.3 nmol X mg protein-1 .30 min-1. Additions of valerate, butyrate, or succinate increased this rate by factors of 2-3 without affecting cellular ATP levels or net fluid absorption (Jv). Inhibition of ATP production with rotenone, which we have previously shown to inhibit Jv [Am. J. Physiol. 243 (Renal Fluid Electrolyte Physiol. 12): F133-F140, 1982], greatly decreased the gluconeogenic rate, but this was modulated by the type of gluconeogenic substrate used. Increasing Na-K-ATPase activity with nystatin or decreasing it with ouabain had widely differing effects, which also depended on the substrate regimen. We conclude that the interaction between gluconeogenesis and active sodium transport cannot be described by a simple competition for ATP. Rather, under normal circumstances, the renal proximal tubule can meet the energetic demands of both gluconeogenesis and sodium transport, and control of these processes is multifactorial and sensitive to fatty acid metabolism.

Ion selectivity and proximal salt reabsorption

1978 ◽  
Vol 235 (3) ◽  
pp. F234-F245 ◽  
Author(s):  
C. A. Berry ◽  
D. G. Warnock ◽  
F. C. Rector
Keyword(s):  
Active Transport ◽  
Sodium Transport ◽  
Ion Selectivity ◽  
Electrical Potential ◽  
Great Majority ◽  
Active Sodium ◽  
Experimental Conditions ◽  
Active Sodium Transport ◽  
Luminal Perfusion ◽  
The Difference

Electrophysiological techniques were used in isolated perfused superficial (S) and juxtamedullary (JM) rabbit proximal convoluted tubules (PCT) to examine the relative sodium-to-chloride (PNa/PCl) and bicarbonate-to-chloride (PHCO3/PCl) permeability ratios. We found that the great majority of PCT are sodium selective and that PHCO3/PCl depends on the experimental conditions. In the presence of active sodium transport, PHCO3/PCl is high and increases with PNa/PCl. When PHCO3/PCl is determined after inhibition of active sodium transport or at 25 degrees C, PHCO3/PCl approximates the free solution anion mobility ratio of 0.5 and is independent of PNa/PCl. The difference between PHCO3/PCl determined in the presence of and in the absence of active transport suggests that the lowering of bath bicarbonate concentration in the presence of active transport changes both paracellular and transcellular current flow. In addition, we found that during luminal perfusion with high chloride, low bicarbonate, organic solute-free solutions, the transepithelial electrical potential depends on PNa/PCl and PHCO3/PCl. This potential is approximately 4.0 mV in S PCT with low PNa/PCl and falls progressively to zero in JM PCT with high PNa/PCl. From these data we conclude that anion concentration gradients drive an important diffusive flux of sodium chloride through the paracellular pathway only in PCT with low PNa/PCl ratios.

Beta 2-adrenergic function in cultured rat proximal tubule epithelial cells

1996 ◽  
Vol 271 (1) ◽  
pp. F71-F77 ◽  
Author(s):  
H. Singh ◽  
S. Linas
Keyword(s):  
Epithelial Cells ◽  
Atpase Activity ◽  
Proximal Tubule ◽  
Sodium Transport ◽  
Cultured Cells ◽  
Proximal Tubules ◽  
Beta 2 ◽  
Acid Loading ◽  
Rat Proximal Tubule ◽  
Stimulation Of

We conducted studies to determine whether functional beta 2-adrenoceptors are present in cultured rat proximal tubule epithelial cells. To determine whether cultured cells maintain polarity with respect to sodium transport, cells were acid loaded. Acid loading resulted in stimulation of sodium transport. Exposure of acid-loaded cells to alkaline extracellular pH further enhanced sodium transport (22Na flux at pH 7.50 was 68.1 +/- 44% above pH 7.00, P < 0.05). Cultured proximal tubules also exhibited basolateral 86Rb uptake, 65% of which was ouabain sensitive. Thus cultured cells maintain apical Na/H antiport and basolateral Na-K-adenosinetriphosphatase (Na-K-ATPase). Metaproterenol (10(-6) M), a selective beta 2-agonist, stimulated Na-K-ATPase activity by 36 +/- 6% above control (P < 0.05). The stimulatory effect was blocked by ICI-118551, a selective beta 2-antagonist. To determine whether metaproterenol-dependent increases in Na-K-ATPase were dependent on apical sodium entry, apical entry was blocked with dimethylamiloride or maximized with monensin. Both dimethylamiloride and monensin prevented metaproterenol activation of Na-K-ATPase. Metaproterenol-mediated increases in Na-K-ATPase activity were associated with increases in sodium transport (27 +/- 10% above control, P < 0.05), which was prevented by dimethylamiloride. In contrast to isoproterenol, metaproterenol did not stimulate cAMP production. In summary, we have shown that functional beta 2-adrenoceptors are present on cultured rat proximal tubules. beta 2-Adrenoceptor activation results in increases in Na-K-ATPase and Na transport as a consequence of increased apical sodium entry.

scholarly journals Developmental changes in rabbit proximal straight tubule paracellular permeability

2002 ◽  
Vol 283 (3) ◽  
pp. F525-F531 ◽  
Author(s):  
Raymond Quigley ◽  
Michel Baum
Keyword(s):  
Proximal Tubule ◽  
Chloride Transport ◽  
Chloride Concentration ◽  
Chloride Ions ◽  
Proximal Tubules ◽  
Chloride Permeability ◽  
Proximal Straight Tubule ◽  
Nephron Segment ◽  
Proximal Tubular

The early proximal tubule preferentially reabsorbs organic solutes and bicarbonate over chloride ions, resulting in a luminal fluid with a higher chloride concentration than that in blood. From this late proximal tubular fluid, one-half of NaCl reabsorption by the adult proximal tubule is active and transcellular and one-half is passive and paracellular. The purpose of the present in vitro microperfusion study was to determine the characteristics of passive chloride transport and permeability properties of the adult and neonatal proximal straight tubules (PST). In tubules perfused with a late proximal tubular fluid, net passive chloride flux was 131.7 ± 37.7 pmol · mm−1 · min−1in adult tubules and −17.1 ± 23.3 pmol · mm−1 · min−1 in neonatal proximal tubules ( P < 0.01). Chloride permeability was 10.94 ± 5.21 × 10−5 cm/s in adult proximal tubules and −1.26 ± 1.84 × 10−5 cm/s in neonatal proximal tubules ( P< 0.05). Thus neonatal PST have a chloride permeability not different from zero and have no net passive chloride transport. Bicarbonate permeability is also less in neonates than adults in this segment (−0.07 ± 0.03 × 10−5 vs. 0.93 ± 0.27 × 10−5 cm/s, P < 0.01). Neonatal PST have higher sodium-to chloride and bicarbonate-to-chloride permeability ratios than adult PST. However, mannitol and sucrose permeabilities were not different in adult proximal tubules and neonatal PST. Transepithelial resistance was measured using current injection and cable analysis. The resistance was 6.7 ± 0.7 Ω · cm2 in adult tubules and 11.3 ± 1.4 Ω · cm2 in neonatal PST ( P < 0.01). In conclusion, there are significant maturational changes in the characteristics of the PST paracellular pathway affecting transport in this nephron segment.

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

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.

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

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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