scholarly journals Effect of estrogen on calcium and sodium transport by the nephron luminal membranes

2001 ◽  
Vol 170 (2) ◽  
pp. 441-450 ◽  
Author(s):  
MG Brunette ◽  
M Leclerc
Keyword(s):  
Membrane Vesicles ◽  
Distal Tubule ◽  
Maximal Effect ◽  
Osteoporosis Prevention ◽  
Na Transport ◽  
High Affinity ◽  
Distal Tubules ◽  
Dose Dependent ◽  
Filtration Technique ◽  
Na Uptake

Estrogens are widely used for contraception and osteoporosis prevention. The aim of the present study was to investigate the effect of 17 beta-estradiol on calcium (Ca(2+)) transport by the nephron luminal membranes, independently of any other Ca(2+)-regulating hormones. Proximal and distal tubules of rabbit kidneys were incubated with 17 beta-estradiol or the carrier for various periods of time, and the luminal membranes of these tubules were purified and vesiculated. Ca(2+) uptake by membrane vesicles was measured using the Millipore filtration technique. Incubation of proximal tubules with the hormone did not influence Ca(2+) uptake by the luminal membranes. In contrast, incubation of distal tubules with 10(-8) M 17 beta-estradiol for 30 min decreased the initial uptake of 0.5 mM Ca(2+) from 0.34+/-0.04 (s.e.m. ) to 0.17+/-0.04 pmol/microg per 5 s (P<0.05). In the presence of 100 mM Na(+), 0.5 mM Ca(2+) uptake was strongly diminished and the effect of 17 beta-estradiol disappeared (0.17+/-0.01 and 0.21+/-0.07 pmol/microg per 5 s in vesicles from the control and treated tubules). Direct incubation of the membranes with 17 beta-estradiol, however, failed to show any influence of the hormone on Ca(2+) transport. The action of 17 beta-estradiol was dose-dependent, with a half-maximal effect at approximately 10(-9) M. Ca(2+) uptake by the distal tubule membranes presents dual kinetics. 17 beta-Estradiol decreased the V(max) value of the high-affinity component from 0.42+/-0.02 to 0.31+/-0.03 pmol/microg per 10 s (P<0.02). In contrast with the effect of the hormone on Ca(2+) transport, estradiol increased Na(+) uptake by both the proximal and distal tubule luminal membranes. In conclusion, incubation of proximal and distal tubules with estrogen decreases Ca(2+) reabsorption by the high-affinity Ca(2+) channels of the distal luminal membranes, and enhances Na(+) transport by the membranes from proximal and distal nephrons.

scholarly journals Phosphophloretin sensitivity of rabbit renal NaPi-IIa and NaPi-Ia

2004 ◽  
Vol 286 (5) ◽  
pp. F955-F964 ◽  
Author(s):  
Brian E. Peerce ◽  
Brandon Peerce ◽  
Rebecca D. Clarke
Keyword(s):  
Renal Cortex ◽  
Phosphate Uptake ◽  
Ph Dependence ◽  
Membrane Vesicles ◽  
Distal Tubule ◽  
Proximal Tubules ◽  
Dependent Manner ◽  
Renal Brush Border Membrane ◽  
Distal Tubules ◽  
Dose Dependent

The effect of phosphorylated phloretins on Na+-dependent phosphate uptake into rabbit renal brush-border membrane vesicles (BBMV) was examined. Na+-dependent phosphate uptake into isolated rabbit cortex BBMV was sensitive to 2′-phosphophloretin (2′-PP) and 2′-phospho-4′,4,6′-trimethoxy phloretin (PTMP) in a dose-dependent and pH-dependent manner. PTMP inhibition of Na+-dependent phosphate uptake was maximum at alkali pH, and 2′-PP inhibition of Na+-dependent phosphate uptake was maximum at acidic pH. Increasing Na+ concentrations did not increase PTMP inhibition of renal cortex BBMV Na+-dependent phosphate uptake at pH 6. The effect of phosphophloretins on Na+-dependent phosphate uptake was examined in BBMV isolated from purified proximal tubules and distal tubules. 2′-PP and PTMP inhibition of Na+-dependent phosphate uptake into BBMV isolated from purified proximal tubules was similar to the inhibition seen with BBMV from renal cortex. 2′-PP, but not PTMP, inhibited Na+-dependent phosphate uptake into BBMV isolated from purified distal tubules. The pH dependence of inhibition, the absence of PTMP inhibition of Na+-dependent phosphate uptake into distal tubule BBMV, and the inhibition of Na+-dependent phosphate uptake into distal tubule BBMV suggest that NaPi-Ia is 2′-PP sensitive and NaPi-IIa is PTMP sensitive.

Localization of diuretic action in microperfused rat distal tubules: Ca and Na transport

1985 ◽  
Vol 248 (4) ◽  
pp. F527-F535 ◽  
Author(s):  
L. S. Costanzo
Keyword(s):  
Distal Tubule ◽  
Maximal Concentration ◽  
Na Transport ◽  
Tubule Cell ◽  
Ca Transport ◽  
Site Of Action ◽  
Distal Tubules ◽  
Sites Of Action ◽  
Distal Site

Experiments were performed in rats to examine the distal site of action of thiazide diuretics and the additive hypocalciuric properties of thiazides and amiloride. In clearance experiments, the maximal natriuretic and hypocalciuric dose of chlorothiazide was established. When amiloride was added, there was further augmentation of Ca reabsorption (P less than 0.025) but no additional natriuresis. Amiloride blunted thiazide-induced kaliuresis (P less than 0.001). Localization of the thiazide effect was studied in early and late distal tubules microperfused in vivo with control and thiazide-containing solutions. The maximally effective luminal drug concentration, 5 X 10(-4) M, inhibited Na transport (P less than 0.001) and enhanced Ca transport (P less than 0.01) in the early distal segments; late segments were on the average unaffected. It is suggested that thiazides interact with the distal convoluted tubule cell, whose predominant location is the early distal tubule. In two long distal tubules, with early and late segments, a maximal concentration of chlorothiazide increased Ca transport and decreased Na transport. Addition of 10(-5) M amiloride caused an additional increment in Ca reabsorption. As amiloride's action is located in the late distal tubule, it is suggested from these experiments that a basis for additive hypocalciuric actions of thiazides and amiloride is separate sites of action in the distal tubule.

High-affinity paroxetine binding to the human placental serotonin transporter

1990 ◽  
Vol 259 (2) ◽  
pp. C196-C204 ◽  
Author(s):  
D. R. Cool ◽  
F. H. Leibach ◽  
V. Ganapathy
Keyword(s):  
Serotonin Transporter ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Binding Capacity ◽  
Membrane Vesicles ◽  
Dependent Manner ◽  
High Affinity ◽  
Paroxetine Binding ◽  
Dose Dependent ◽  
Dissociation Constant Kd

We investigated the interaction of paroxetine, a nontricyclic antidepressant, with the serotonin transporter of the human placental brush-border membrane. Paroxetine bound to the purified placental brush-border membranes with a high affinity [dissociation constant (Kd) = 72 pM]. The maximal binding capacity (Bmax) was 3.9 pmol/mg protein. Imipramine, desipramine, and serotonin inhibited the binding in a dose-dependent manner with inhibition constant (Ki) values of 4.4 nM, 48.7 nM, and 1.77 microM, respectively, whereas reserpine, ketanserin, and 5-hydroxytryptophan did not have any effect. Imipramine and serotonin inhibited paroxetine binding by increasing the Kd with essentially no effect on Bmax. Binding of paroxetine to the membranes increased hyperbolically with increasing concentrations of Na+ in the assay medium. Cl- had little effect on the binding. The effect of Na+ was primarily to increase the affinity of the transporter for paroxetine with no effect on Bmax. The association constant (Ka) increased hyperbolically as the concentration of Na+ increased, indicating a 1Na+:1paroxetine stoichiometry. The maximal value for Ka was 12.1 +/- 2.5 x 10(12) M-1, and Kd for Na+ was 10.0 +/- 3.5 mM. Treatment of the membranes with tyrosyl group-specific reagents reduced the Na(+)-dependent binding, suggesting the involvement of tyrosyl residues in the binding process. This inhibition was, however, significantly reduced when treatment with the reagent was performed in the presence of Na+, suggesting that the reactive tyrosyl residues were located at or near the Na(+)-binding site. Paroxetine inhibited NaCl gradient-dependent serotonin uptake in placental brush-border membrane vesicles both at pH 6.5 and 7.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of colonic Na+ transport by amiloride analogues

1989 ◽  
Vol 256 (1) ◽  
pp. C67-C74 ◽  
Author(s):  
R. J. Bridges ◽  
E. J. Cragoe ◽  
R. A. Frizzell ◽  
D. J. Benos
Keyword(s):  
Kinetic Analysis ◽  
Colonic Mucosa ◽  
Short Circuit ◽  
Membrane Vesicles ◽  
Short Circuit Current ◽  
Pharmacological Profile ◽  
Na Transport ◽  
Lower Affinity ◽  
High Affinity ◽  
22Na Uptake

The potency of several amiloride analogues to inhibit electrogenic Na+ transport in colon from dexamethasone-treated rats was compared. Short-circuit current (Isc) across the colonic mucosa and 22Na+ uptake into membrane vesicles derived from colonic enterocytes was determined in dexamethasone-treated rats. Kinetic analysis of inhibition of Isc and 22Na+ uptake revealed the presence of a high- and low-affinity amiloride pathway. One pathway had a high affinity [(Ki-Isc; Ki uptake] to benzamil (15.5 nM; 5.4 nM), phenamil (19.4 nM; 7.0 nM), 3',4'-dichlorobenzamil (29.0 nM; 25.2 nM), and amiloride (115 nM; 12.4 nM) but a much lower affinity to 5-(N-ethyl-N-isopropyl)amiloride (EIPA) (greater than 100 microM; greater than 9.9 microM) and 5-(N-propyl-N-butyl)-2'-4'-dichlorobenzamil (PBDCB) (greater than microM; greater than 32.8 microM). The high-affinity pathway accounted for 75-83% of the transport of Na+. The second pathway had nearly the same low affinity for each of the analogues (e.g., amiloride Ki-Isc 1 microM; Ki uptake 4 microM) and accounted for only 15-25% of the transport of Na+. The results demonstrate that the structure-inhibitory pattern of these amiloride analogues for the high-affinity pathway is the pattern observed in other electrogenic Na+-transporting epithelia and that this pharmacological profile is preserved in membrane vesicles derived from colonic enterocytes. In addition, the potency of EIPA and benzamil to inhibit electroneutral Na+ transport across the colon from normal rats (i.e., not treated with dexamethasone) was also investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Renal transport of neutral amino acids. Cation-dependent uptake of l-alanine by luminal-membrane vesicles

1987 ◽  
Vol 248 (2) ◽  
pp. 533-538 ◽  
Author(s):  
K E Jørgensen ◽  
M I Sheikh
Keyword(s):  
Transport System ◽  
Membrane Vesicles ◽  
Transport Systems ◽  
Physiological Importance ◽  
High Affinity ◽  
Luminal Membrane ◽  
Alanine Transport ◽  
Pars Recta ◽  
Pars Convoluta ◽  
Filtration Technique

The characteristics of L-alanine transport in luminal-membrane vesicles isolated either from whole cortex or from pars convoluta or pars recta of rabbit proximal tubules were studied by a rapid filtration technique and by a spectrophotometric method. Uptake of L-alanine by vesicles from whole cortex was mediated by both Na+-dependent and Na+-independent, but electrogenic, processes. The nature, mechanism and tubular localization of the transport systems were studied by the use of vesicles derived from pars convoluta and pars recta. In vesicles from pars recta transport of L-alanine was strictly dependent on Na+ and occurred via a dual transport system, namely a high-affinity (half-saturation 0.14 mM) and a low-affinity system (half-saturation 9.6 mM). The cation-dependent but Na+-unspecific transport system for L-alanine was exclusively localized to the pars convoluta, which also contained an Na+-preferring system of intermediate affinity (half saturation 2.1 mM). A closer examination of the mechanism of transport of L-alanine in vesicles from pars convoluta revealed that an H+ gradient (extravesicular greater than intravesicular) can drive the transport of L-alanine into the vesicles both in the presence and in the absence of Na+. The physiological importance of various L-alanine transporters is briefly discussed.

Pancreas growth, tyrosine kinase, PtdIns 3-kinase, and PLD involve high-affinity CCK-receptor occupation

1994 ◽  
Vol 266 (1) ◽  
pp. G62-G70 ◽  
Author(s):  
N. Rivard ◽  
G. Rydzewska ◽  
J. S. Lods ◽  
J. Martinez ◽  
J. Morisset
Keyword(s):  
Tyrosine Kinase ◽  
Trophic Factors ◽  
Maximal Effect ◽  
Promoting Effect ◽  
Pancreatic Acini ◽  
High Affinity ◽  
Dose Dependent ◽  
Dose Dependent Effect

Cholecystokinin (CCK), CCK octapeptide (CCK-8), and caerulein (Cae) are the most potent trophic factors in the pancreas when given exogenously or released from the intestine. Recent studies have suggested that this growth-promoting effect of CCK was initiated through the occupation of the CCKA receptor. This study was then undertaken to determine whether occupation of the high- or low-affinity CCKA receptor is involved in the growth process and to establish which transduction signals have been selectively activated. As an answer to the first question, rats were infused with CCK JMV-180, a CCKA high-affinity agonist, at doses of 50, 100, 150, and 300 micrograms.kg-1.h-1, or Cae (0.25 micrograms.kg-1.h-1) for 4 days. After rats were killed, their pancreatic weight and contents of protein, DNA, RNA, amylase, and chymotrypsinogen were estimated. To investigate the transduction signals, rats were infused for 30 min to 4 h with 300 micrograms.kg-1.h-1 JMV-180, or pancreatic acini were exposed in vitro to 1 microM JMV-180 for 5 or 30 min. After rats were killed, pancreases were used to monitor tyrosine kinase, phosphatidylinositol (PtdIns) 3-kinase, and phospholipase D (PLD) activities. The first set of experiments indicates that JMV-180 caused a dose-dependent effect on pancreas growth, with the 300 micrograms.kg-1 x h-1 dose giving the maximal effect comparable to that of Cae. Furthermore, JMV-180 induced concomitant early increases in tyrosine kinase and PLD activities both in vivo and in vitro and PtdIns 3-kinase in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Sodium/proton antiport in brush-border-membrane vesicles isolated from rat small intestine and kidney

1976 ◽  
Vol 154 (3) ◽  
pp. 597-604 ◽  
Author(s):  
H Murer ◽  
U Hopfer ◽  
R Kinne
Keyword(s):  
Small Intestine ◽  
Brush Border ◽  
Incubation Medium ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Na Transport ◽  
Carbonyl Cyanide ◽  
Triton X ◽  
Na Uptake ◽  
Renal Brush Border

Studies on proton and Na+ transport by isolated intestinal and renal brush-border-membrane vesicles were carried out to test for the presence of an Na+/H+-exchange system. Proton transport was evaluated as proton transfer from the intravesicular space to the incubation medium by monitoring pH changes in the membrane suspension induced by sudden addition of cations. Na+ transport was determined as Na+ uptake into the vesicles by filtration technique. A sudden addition of sodium salts (but not choline) to the membrane suspension provokes an acidification of the incubation medium which is abolished by the addition of 0.5% Triton X-100. Pretreatment of the membranes with Triton X-100 prevents the acidification. The acidification is also not observed if the [K+] and proton conductance of the membranes have been increased by the simultaneous addition of valinomycin and carbonyl cyanide p-trifluoromethoxyphenylhydrazone to the K+-rich incubation medium. Either valinomycin or carbonyl cyanide p-trifluoromethoxyphenylhydrazone when added alone do not alter the response of the membranes to the addition of Na+. Na+ uptake by brush-border microvilli is enhanced in the presence of a proton gradient directed from the intravesicular space to the incubation medium. Under these conditions a transient accumulation of Na+ inside the vesicles is observed. It is concluded that intestinal and renal brush-border membranes contain a NA+/H+ antiport system which catalyses an electroneutral exchange of Na+ against protons and consequently can produce a proton gradient in the presence of a concentration difference for Na+. This system might be involved in the active proton secretion of the small intestine and the proximal tubule of the kidney.

Renal sodium transport in vitamin D resistant hypophosphatemic rickets

1985 ◽  
Vol 63 (10) ◽  
pp. 1339-1344 ◽  
Author(s):  
Michèle G. Brunette ◽  
Ghazi El Mernissi ◽  
Alain Doucet
Keyword(s):  
Vitamin D ◽  
Atpase Activity ◽  
Incubation Medium ◽  
Basolateral Membrane ◽  
Distal Tubule ◽  
Hypophosphatemic Rickets ◽  
Na Transport ◽  
Control Activity ◽  
Renal Brush Border Membrane ◽  
Na Uptake

To investigate the possible role of a Na transport defect in the pathogenesis of the phosphaturia in vitamin D resistant rickets, we studied the activity of the Na–K ATPase activity along the microdissected segments of the nephron in normal (N) and hypophosphatemic mice (Hyp), the Na uptake by renal brush border membrane (BBM), as well as the interrelationship between Na and phosphate transport through this membrane. In N mice, Na-K ATPase activity was present in decreasing order, in the distal tubule, the ascending branch of the loop of Henle, the proximal tubule, and the collecting tubule. In Hyp mice, the Na–K ATPase activity was comparable to that measured in N mice, except in the granular segment of the distal tubule where a 256% of the control activity was reproducibly observed. In N mice, Na initial uptake by BBM vesicles increased with Na concentration in the incubation medium, according to two kinetic components: one saturable, evident at low substrate concentrations and the other, nonsaturable, corresponding to a passive diffusion. The addition of 5 mM PO4 in the incubation medium did not significantly influence Na transport. In contrast, Na concentration in the incubation medium largely modified the kinetics of PO4 uptake: increasing Na concentration enhanced PO4 uptake and decreased the apparent Km. In Hyp mice, Na uptake by BBM was identical to that observed in N mice, but PO4 uptake was decreased by half. Na concentration in the incubation medium similarly influenced PO4 uptake in N and Hyp mice, and the Km values at each concentration of Na were comparable in the two series of animals. It is concluded that the defect in PO4 transport in Hyp mice is not secondary to an alteration of Na transport through the BBM, nor to an abnormal relationship between Na and PO4 in the PO4 carrier system, nor to a decreased Na–K ATPase activity in the basolateral membrane of the cell. The increase in Na–K ATPase in the distal tubule is probably a secondary phenomenon, not directly related to the pathogenesis of the disease.

Characterization of ATP-dependent Ca2+ transport in the basolateral membrane vesicles from proximal and distal tubules of the rabbit kidney

1991 ◽  
Vol 69 (2-3) ◽  
pp. 109-114 ◽  
Author(s):  
Chidambaram Ramachandran ◽  
Meanthan Chan ◽  
Michèle G. Brunette
Keyword(s):  
Transport System ◽  
Ph Dependence ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Distal Tubule ◽  
Optimal Concentration ◽  
Rabbit Kidney ◽  
Maximal Velocity ◽  
Basolateral Membrane Vesicles ◽  
Distal Tubules

Basolateral membrane vesicles were prepared from purified proximal and distal tubules of the rabbit kidney. The properties of the ATP-dependent Ca2+ transport were investigated. In both membranes, there was a high affinity, ATP-dependent Ca2+ transport system (Km = 0.1 μM). The optimal concentration of Mg2+ was 0.5 mM and the optimal concentration of ATP was 1 mM. The nucleotide specificity and pH dependence of the Ca2+ transport in both membranes were similar. In basolateral membrane vesicles, calmodulin had no effect on Ca2+ transport. However, in basolateral membrane vesicles depleted of calmodulin, exogeneous calmodulin increased the Ca2+ transport by increasing maximal velocity. There were no major differences in the properties of the ATP-dependent Ca2+ transport system in these two membranes. These findings are discussed in relation to why parathyroid hormone differentially modulates Ca2+ transport in these two segments of the nephron.Key words: Ca2+ transport, ATP-dependent, kidney, proximal tubule, distal tubule, basolateral membrane.

scholarly journals Downregulation of high-affinity potassium and sodium symporter gene, EcHKT1;1, in Eucalyptus roots enhances salt tolerance

2021 ◽  
Author(s):  
BALASUBRAMANIAN Aiyar ◽  
Selvakesavan Rajendran kamalabai ◽  
Shamili Krishnaraj ◽  
Sandhya M C ◽  
Usha Jayachandran ◽  
...  
Keyword(s):  
Salt Tolerance ◽  
Tree Species ◽  
External Medium ◽  
Major Gene ◽  
In Planta ◽  
Na Transport ◽  
High Affinity ◽  
Na Uptake ◽  
Transgenic Plantlets

Engineering for restricted root Na+ uptake could potentially enhance salt tolerance in Eucalyptus. High-affinity K+ transporters (HKTs) have been implicated in Na+ uptake from the external medium as in the case of TaHKT2;1 or in the unloading of Na+ from xylem like in AtHKT1;1. To rapidly determine the in planta role of EcHKT1:1, composite transgenics in which EcHKT1:1 was specifically downregulated via RNAi in the roots were generated. Compared to the controls that failed to survive at 350 mM NaCl, 33 % of the composite transgenic plantlets generated using the EcHKT1;1 silencing construct were able to tolerate up to 400 mM NaCl. In these composite transgenics, EcHKT1;1 downregulation ranged from 37 % to 74 %. The average shoot to root ratio of sodium was 4.9 folds lower than the controls indicating restricted translocation of Na+ to the shoots. Relative expression analysis in the leaves of two non-transgenic genotypes contrasting for their salt tolerance also showed downregulated EcHKT1;1 expression in the tolerant clone. The study thus determined that EcHKT1;1 is a major gene determining Na+ transport from the roots to shoots. This study also demonstrated the utility of the composite transgenic approach for screening genes conferring salt tolerance in tree species.

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