Evidence for active and passive urate transport in the rat proximal tubule

1981 ◽  
Vol 240 (2) ◽  
pp. F90-F93
Author(s):  
E. J. Weinman ◽  
H. O. Senekjian ◽  
S. C. Sansom ◽  
D. Steplock ◽  
A. Sheth ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Active Transport ◽  
Transport Process ◽  
Permeability Coefficient ◽  
Electrical Potential ◽  
Electrical Potential Difference ◽  
Passive Permeability ◽  
Peritubular Capillaries ◽  
Active Transport Process ◽  
Rat Proximal Tubule

Studies utilizing the technique of simultaneous microperfusion of peritubular capillaries and tubular lumen of the proximal tubule of the rat were performed to determine if the absorption of urate was an active transport process and to determine the passive permeability coefficient for urate. When radioactive urate of equal specific activity and concentration was present in both perfusion solutions, the ratio of collected to initial concentrations of urate in the luminal perfusate (CO/CI) was 0.71 +/- 0.02. This gradient was higher than that predicted at equilibrium from the electrical potential difference determined in the in vitro perfused rabbit proximal tubule. The addition of para-chloromercuribenzoate (PCMB) to both solutions resulted in a significantly higher CO/CI of 0.90 +/- 0.02. This latter value is closer to the value predicted at electrochemical equilibrium. In separate studies, the unidirectional fluxes of urate were determined in the presence of PCMB. The calculated passive permeability coefficient averaged approximately 0.94 pmol . min-1 . mm-1 . mM-1 and was equal in both directions. These results indicate that in the rat proximal tubule urate absorption is an active transport process. In addition, there exists a passive permeation pathway for urate movement out of and into the proximal tubule.

A nuclear localization signal can enhance both the nuclear transport and expression of 1 kb DNA

1999 ◽  
Vol 112 (12) ◽  
pp. 2033-2041
Author(s):  
J.J. Ludtke ◽  
G. Zhang ◽  
M.G. Sebestyen ◽  
J.A. Wolff
Keyword(s):  
Active Transport ◽  
Nuclear Localization ◽  
Transport Process ◽  
Nuclear Transport ◽  
Passive Diffusion ◽  
Viral Gene ◽  
Nuclear Localization Signals ◽  
Size Limit ◽  
Cytosolic Extract ◽  
Active Transport Process

Although the entry of DNA into the nucleus is a crucial step of non-viral gene delivery, fundamental features of this transport process have remained unexplored. This study analyzed the effect of linear double stranded DNA size on its passive diffusion, its active transport and its NLS-assisted transport. The size limit for passive diffusion was found to be between 200 and 310 bp. DNA of 310–1500 bp entered the nuclei of digitonin treated cells in the absence of cytosolic extract by an active transport process. Both the size limit and the intensity of DNA nuclear transport could be increased by the attachment of strong nuclear localization signals. Conjugation of a 900 bp expression cassette to nuclear localization signals increased both its nuclear entry and expression in microinjected, living cells.

Reflection coefficients and water permeability in rat proximal tubule

1989 ◽  
Vol 257 (4) ◽  
pp. F658-F668 ◽  
Author(s):  
R. Green ◽  
G. Giebisch
Keyword(s):  
Proximal Tubule ◽  
Water Permeability ◽  
Significant Contribution ◽  
Water Flux ◽  
Reflection Coefficients ◽  
Ionic Fluxes ◽  
Peritubular Capillaries ◽  
Solute Movement ◽  
Rat Proximal Tubule ◽  
Net Water Flux

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reflection coefficients. All perfusates contained cyanide to inhibit active transport; the tubular perfusate was isotonic and the peritubular capillaries were perfused with solutions made hypertonic with NaCl, NaHCO3, L-glucose, or sodium ferrocyanide. Measurements of recollected fluid enabled a precise mean gradient and ionic fluxes to be calculated; net water flux was measured with inulin. Imposed gradients always partly dissipated. Reflection coefficients were 0.59 +/- 0.01 for NaCl, 0.87 +/- 0.04 for NaHCO3-, and 0.96 +/- 0.07 for ferrocyanide, assuming that L-glucose was 1. Water permeability of the proximal tubule was 1,030 microns/s. Ionic permeability of Cl- (21.6 +/- 1.3 X 10(-5) cm/s) was greater than that for Na+ (13.3 +/- 2.7 X 10(-5) cm/s); permeability for L-glucose was 5.4 +/- 1.3 X 10(-5), and for ferrocyanide ions 2.7 +/- 0.9 X 10(-5) cm/s. It is concluded that in rat proximal tubule both NaCl and NaHCO3 have reflection coefficients less than 1.0 and solute asymmetry across the epithelium is a significant driving force for fluid reabsorption. Furthermore the data suggest that there is a significant contribution of solvent drag to solute movement.

Total contents and net movements of magnesium in the rat uterus

1971 ◽  
Vol 220 (6) ◽  
pp. 2067-2067
Author(s):  
A. H. Moawad ◽  
E. E. Daniel
Keyword(s):  
Membrane Potential ◽  
Active Transport ◽  
Extracellular Space ◽  
Transport Process ◽  
Electrochemical Gradient ◽  
Rat Uterus ◽  
Active Transport Process

Page 75: A. H. Moawad and E. E. Daniel. "Total contents and net movements of magnesium in the rat uterus." Page 80, column 2, line 44, involving the calculation of Vm the answer to the equation, –0.067 V, should read, "–0.012 V." Page 80, column 2, lines 49–54 should read, "The calculated magnesium equilibrum potential is less than the observed membrane potential, which is about 0.050 V. Therefore, some of the tissue magnesium may be excluded by an active transport process against an electrochemical gradient or by loose binding in the extracellular space."

Ionic regulation of Na absorption in proximal colon: cation inhibition of electroneutral Na absorption

1987 ◽  
Vol 252 (1) ◽  
pp. G100-G108
Author(s):  
J. H. Sellin ◽  
R. De Soignie
Keyword(s):  
Linear Function ◽  
Active Transport ◽  
Transport Process ◽  
Proximal Colon ◽  
High Rate ◽  
Ionic Regulation ◽  
Diffusional Flux ◽  
Active Transport Process

Active Na absorption (JNanet) in rabbit proximal colon in vitro is paradoxically stimulated as [Na] in the bathing media is lowered with constant osmolarity. At 140 mM [Na]o, JNanet is -0.6 +/- 0.4 mueq X cm-2 X h-1, whereas at 50 mM [Na]o JNanet is 5.0 +/- 0.7 mueq X cm-2 X h-1, P less than 0.01. JNas----m is a linear function of [Na]o, suggesting a diffusional flux. JNam----s increases almost linearly from 0 to 50 mM [Na]o but then plateaus and actually decreases from 50 to 140 mM [Na]o, consistent with inhibition of an active transport process. Both lithium and Na are equally effective inhibitors of JNanet, whereas choline and mannitol do not block the high rate of JNanet observed in decreased [Na]o. Either gluconate or proprionate replacement of Cl inhibits JNanet. Removal of K or HCO3 does not alter Na absorption. JNanet at lowered [Na]o is electrically silent and is accompanied by increased Cl absorption; it is inhibited by 10(-3) M amiloride and 10(-3) M theophylline but not by 10(-4) M bumetanide. Epinephrine is equally effective at stimulating Na absorption at 50 and 140 mM [Na]; yohimbine does not inhibit JNanet at 50 mM [Na]o. Na gradient experiments are consistent with a predominantly serosal effect of the decreased [Na]o. These results suggest that Na absorption in rabbit proximal colon in vitro is stimulated by decreased [Na]; the effect is cation specific, both Na and Li blocking the stimulatory effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of stimulation of proximal tubule chloride transport by formate and oxalate

1996 ◽  
Vol 271 (2) ◽  
pp. F446-F450 ◽  
Author(s):  
T. Wang ◽  
A. L. Egbert ◽  
T. Abbiati ◽  
P. S. Aronson ◽  
G. Giebisch
Keyword(s):  
Proximal Tubule ◽  
Chloride Transport ◽  
Rat Kidney ◽  
Exchange Process ◽  
Exchange Inhibitor ◽  
Volume Absorption ◽  
Peritubular Capillaries ◽  
Rat Proximal Tubule ◽  
Stimulation Of

We have previously demonstrated that formate and oxalate stimulate volume absorption in the rat proximal tubule, consistent with Cl-/formate and Cl-/oxalate exchange process across the apical membrane. To sustain Cl- absorption by these processes requires mechanisms for recycling formate and oxalate from lumen to cell. The aims of the present study were to characterize these mechanisms of formate and oxalate recycling. Proximal tubules and peritubular capillaries were simultaneously microperfused in the rat kidney in situ. Serum formate concentration was determined to be 56.5 +/- 7.7 microM. Addition of 5, 50, and 500 microM formate to both luminal and capillary perfusates significantly increased net Cl- absorption (Jcl) by 26, 26, and 46%, respectively. Jcl was stimulated 38% by 1 microM oxalate added to the perfusates. Removal of sulfate completely prevented the stimulation of Jcl by 1 microM oxalate but had no effect on the stimulation of Jcl by formate. Luminal addition of the Na+/H+ exchange inhibitor ethylisopropylamiloride completely blocked the stimulation of Jcl by 50 microM formate but had no effect on stimulation by oxalate. We conclude that physiological concentrations of formate and oxalate markedly stimulate Cl- and fluid absorption in the rat proximal convoluted tubule. Whereas formate recycling most likely involves Na+/H+ exchange in parallel with H(+)-coupled formate entry, oxalate recycling involves sodium-sulfate cotransport in parallel with sulfate/oxalate exchange.

Effects of formate and oxalate on volume absorption in rat proximal tubule

1992 ◽  
Vol 263 (1) ◽  
pp. F37-F42 ◽  
Author(s):  
T. Wang ◽  
G. Giebisch ◽  
P. S. Aronson
Keyword(s):  
Proximal Tubule ◽  
Channel Blocker ◽  
Ringer Solution ◽  
Proximal Tubules ◽  
Solution Ph ◽  
Physiological Range ◽  
Volume Absorption ◽  
Peritubular Capillaries ◽  
Rat Proximal Tubule

We examined the effects of formate and oxalate on the rate of fluid absorption (Jv) in the rat proximal convoluted tubule in situ. Proximal tubules were microperfused with a high-Cl-, low-HCO3- Ringer solution (pH 6.7), and the peritubular capillaries were perfused with a standard Ringer solution (pH 7.4), simulating conditions in the late proximal tubule. Jv, a measure of transtubular NaCl absorption under these conditions, was calculated from the change in luminal [3H]inulin. Addition of formate in the physiological range (500 microM) to the luminal perfusate increased Jv by 45%; addition of 500 microM formate to both luminal and capillary perfusates increased Jv by 57%. Similarly, addition of oxalate in the physiological range (5 microM) to the luminal perfusate increased Jv by 37%; addition of 5 microM oxalate to both luminal and capillary perfusates increased Jv by 57%. The stimulatory effects of formate and oxalate perfused in the lumen and capillaries were not additive. Addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS, 0.1 mM) to the luminal perfusate had no effect on baseline Jv measured in the absence of added formate and oxalate but completely abolished the increment in Jv induced by formate and oxalate. Addition of the Cl(-)-channel blocker diphenylamine-2-carboxylate (DPC, 0.2 mM) to the capillary perfusate had no effect on baseline Jv but completely abolished the increment in Jv induced by formate and oxalate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of furosemide on the electrical parameters of frog skin

1982 ◽  
Vol 243 (6) ◽  
pp. F581-F587 ◽  
Author(s):  
A. Corcia ◽  
S. R. Caplan
Keyword(s):  
Active Transport ◽  
Frog Skin ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Relative Increase ◽  
Electrical Potential Difference ◽  
Electrical Parameters ◽  
Active Conductance ◽  
Solution Bathing

When added to the mucosal solution bathing isolated frog skin at concentrations ranging from 5 X 10(-4) to 3 X 10(-3) M, the diuretic furosemide increased both the active transport of sodium and the electrical potential difference across the tissue in a dose-dependent way. The same effect was observed in chloride-free solutions. Mucosal furosemide also decreased the passive unidirectional fluxes of chloride. We believe that as far as electrical parameters are concerned mucosal furosemide has a double effect in frog skin: it increases the active conductance to sodium across the mucosal membrane, thus increasing active transport, and decreases the passive permeability to chloride, thus altering the passive conductance of the skin. The relative increase in short-circuit current was, however, invariably greater than the increase of the active conductance, suggesting the influence of yet a third effect. The effect of mucosal furosemide on active sodium transport was blocked by amiloride (5 X 1-(-5) M) and was independent of vasopressin. Qualitatively the effect was similar to the effect produced by triphenylmethylphosphonium ion.

Direct evaluation of the permeability of the rat proximal convoluted tubule to CO2

1982 ◽  
Vol 242 (5) ◽  
pp. F470-F476
Author(s):  
M. S. Lucci ◽  
L. R. Pucacco ◽  
N. W. Carter ◽  
T. D. DuBose
Keyword(s):  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Carbonic Acid ◽  
Carbonic Anhydrase Activity ◽  
Proximal Convoluted Tubule ◽  
Direct Evaluation ◽  
Carbon Dioxide Gas ◽  
Peritubular Capillaries ◽  
Rat Proximal Tubule

Conflicting data exist regarding the ability of the rat proximal convoluted tubule to maintain a transepithelial gradient for CO2 and the effects of carbonic anhydrase on CO2 permeability. The present in vivo microperfusion experiments were designed to assess the ability of the rat proximal tubule to sustain a CO2 gradient between tubule lumen and peritubular blood. Tubules were perfused at rates ranging from 10 to 100 nl/min with isotonic sodium chloride containing no CO2. Peritubular capillary and intraluminal PCO2 was measured during microperfusion with PCO2 microelectrodes to allow determination of the transepithelial CO2 gradient. The mean PCO2 measured in peritubular capillaries of control rats was 60.6 +/- 1.9 mmHg. Since the perfusion solution initially contained no CO2, a gradient of 60 mmHg was imposed across the tubule epithelium. Intraluminal PCO2 rapidly approached that of the surrounding capillaries. At a tubule perfusion rate of 20 nl/min, the gradient between lumen and blood decreased to 0.9 mmHg, a value not significantly greater than zero. The calculated CO2 permeability coefficient (KCO2) was 3.69 X 10(-5) cm2/s. Addition of either 10(-4) M acetazolamide or benzolamide did not prolong the rapid dissipation of the imposed CO2 gradient. The KCO2 during carbonic anhydrase inhibition was not significantly different from control values. It is concluded that the rat proximal tubule does not present a physiologically significant diffusion barrier to CO2 either in the presence or absence of carbonic anhydrase activity. The previously demonstrated acid disequilibrium pH in the proximal tubule during inhibition of carbonic anhydrase represents an intraluminal accumulation of carbonic acid rather than of carbon dioxide gas.

Active Transport of Sulphate Ions by the Malpighian Tubules of Larvae of the Mosquito Aedes Campestris

1975 ◽  
Vol 62 (2) ◽  
pp. 367-378
Author(s):  
S. H. P. MADDRELL ◽  
J. E. PHILLIPS
Keyword(s):  
Active Transport ◽  
Concentration Gradient ◽  
Electrical Potential ◽  
Malpighian Tubules ◽  
Potential Difference ◽  
Electrical Potential Difference ◽  
Sulphate Content ◽  
Anal Papillae ◽  
Tracer Experiments

1. Larvae of Aedes campestris ingest and absorb into their haemolymph large quantities of the sulphate-rich water in which they live, yet they are able to maintain the sulphate content of the haemolymph well below that of the environment. 2. Tracer experiments showed that sulphate regulation was not achieved by deposition of precipitates in the tissues. 3. In vitro preparations of Malpighian tubules secrete sulphate ions actively against both a three times concentration gradient and an electrical potential difference of 20 mV. This transport is half saturated at about 10 mM. 4. The rate of sulphate secretion by the Malpighian tubules is sufficient to remove all of the sulphate ingested by larvae living in waters which contain less than 100 mM of this anion. At higher concentrations, sulphate ions are probably also excreted elsewhere, perhaps by the rectum or anal papillae.

scholarly journals Convective paracellular solute flux. A source of ion-ion interaction in the epithelial transport equations.

1987 ◽  
Vol 89 (3) ◽  
pp. 501-518 ◽  
Author(s):  
A M Weinstein
Keyword(s):  
Proximal Tubule ◽  
Epithelial Transport ◽  
Electrical Potential ◽  
Transport Equations ◽  
Solute Flux ◽  
Reflection Coefficients ◽  
Cross Term ◽  
Parallel Structures ◽  
In Series ◽  
Rat Proximal Tubule

An electrolyte model of an epithelium (a cell and a tight junction in parallel, both in series with a lateral interspace basement membrane) is analyzed using the formalism of nonequilibrium thermodynamics. It is shown that if the parallel structures are heteroporous (i.e., reflection coefficients for two ion species differ between the components), then a cross-term will appear in the overall transport equations of the epithelium. Formally, this cross-term represents an ion-ion interaction. With respect to the rat proximal tubule, data indicating epithelial ionic reflection coefficients less than unity, together with the assumption of no transcellular solvent drag, imply the presence of convective paracellular solute flux. This means that a model applicable to a heteroporous structure must be used to represent the tubule, and, in particular, the cross-terms for ion-ion interaction must also be evaluated in permeability determinations. A series of calculations is presented that permits the estimation of the Na-Cl interaction for rat proximal tubule from available experimental data. One consequence of tubule heteroporosity is that an electrical potential may be substantially less effective than an equivalent concentration gradient in driving reabsorptive ion fluxes.

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