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)

Active transport of Fe59 by everted segments of rat duodenum

1960 ◽  
Vol 198 (3) ◽  
pp. 609-613 ◽  
Author(s):  
Eugene B. Dowdle ◽  
David Schachter ◽  
Harris Schenker
Keyword(s):  
Small Intestine ◽  
Active Transport ◽  
Transport Process ◽  
Transport Mechanism ◽  
Concentration Gradients ◽  
Active Transport Mechanism ◽  
Proximal Small Intestine ◽  
Rat Duodenum ◽  
Active Transport Process

Everted gut sacs prepared from segments of the proximal small intestine of rats transport Fe59 from the mucosal to the serosal surfaces against concentration gradients in vitro. The active transport mechanism is dependent upon oxidative metabolism and the generation of phosphate-bond energy, and is limited in capacity. The active transport process is maximal in the region of the small intestine immediately distal to the pylorus and diminishes with more distal segments of the gut. Addition of ascorbic acid to the incubation medium markedly increases the active transport of Fe59 in vitro.

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.

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."

Bicarbonate secretion by rabbit proximal colon

1986 ◽  
Vol 251 (4) ◽  
pp. G436-G445 ◽  
Author(s):  
S. K. Sullivan ◽  
P. L. Smith
Keyword(s):  
Transport Process ◽  
Short Circuit ◽  
Proximal Colon ◽  
Bathing Solution ◽  
Bicarbonate Secretion ◽  
Rabbit Ileum ◽  
Ussing Chambers ◽  
Ph Stat ◽  
Dependent Mechanism

Stripped segments of proximal colon (1-6 cm distal to the ampulla caecalis coli) were studied in vitro in Ussing chambers under short-circuit conditions using the pH-stat technique. With glucose and HCO3-CO2 present in the serosal bathing solution only, proximal colon alkalinizes the luminal bathing solution at a rate of 2.1 +/- 0.2 mu eq X h-1 X cm-2 (n = 36). With HCO3-CO2 present in the luminal bathing solution alone, proximal colon does not significantly acidify or alkalinize the serosal bathing solution. Addition of glucose (10 mM) to the luminal bathing solution abolished luminal alkalinization. Removal of HCO3 and CO2 from the serosal bathing solution or replacement of O2 with N2 also abolished luminal alkalinization. Acetazolamide (0.1 mM) added to both bathing solutions did not alter the rate of luminal alkalinization. Ion-replacement studies revealed that the alkalinization process was highly dependent on the presence of Na in the bathing solutions and much less dependent on the presence of Cl. Furthermore, ouabain (0.1 mM) significantly reduced luminal alkalinization. As in rabbit ileum, serosal epinephrine (0.1 mM) did not alter luminal alkalinization but increased serosal alkalinization by a Na-dependent mechanism. These results suggest that luminal alkalinization results from a Na-dependent, active transcellular HCO3 transport process and that a Na-dependent HCO3 absorptive process is activated by adrenergic stimuli.

Active transport of quaternary ammonium compounds by the choroid plexus in vitro

1965 ◽  
Vol 208 (4) ◽  
pp. 666-673 ◽  
Author(s):  
Yoshihiro Tochino ◽  
Lewis S. Schanker
Keyword(s):  
Choroid Plexus ◽  
Active Transport ◽  
Quaternary Ammonium ◽  
Transport Process ◽  
Quaternary Ammonium Compounds ◽  
Metabolic Inhibitors ◽  
Solution Ph ◽  
High Concentrations ◽  
Ammonium Compounds

The quaternary ammonium compounds, hexamethonium, decamethonium, and N1-methylnicotinamide (NMN) are taken up by the rabbit choroid plexus in vitro (Krebs-Ringer phosphate glucose solution, pH 7.4, 37 C, oxygen) by a process showing all the characteristics of active transport. Uptake against a concentration gradient occurs by a saturable process that is inhibited by low temperature, by anaerobic conditions, and by low concentrations of ouabain, reserpine, and certain metabolic inhibitors. Decamethonium and NMN act as competitive inhibitors of hexamethonium uptake, suggesting that the three cations share a common transport process. Hexamethonium uptake is dependent on levels of Na, K, Mg, and phosphate in the incubation medium. Hexamethonium and decamethonium, but not NMN, are bound to homogenates of choroid plexus. The characteristics of the binding are such that binding would not account for the bulk of drug accumulation seen in the intact tissue. High concentrations of p-aminohippurate do not inhibit the uptake of hexamethonium. No evidence could be obtained for active uptake of hexamethonium by subcellular particles of plexus homogenates. The transport process for quaternary ammonium compounds appears to be present in the choroid plexus of the dog, cat, and guinea pig as well as in that of the rabbit.

Steroids alter ion transport and absorptive capacity in proximal and distal colon

1985 ◽  
Vol 249 (1) ◽  
pp. G113-G119 ◽  
Author(s):  
J. H. Sellin ◽  
R. C. DeSoignie
Keyword(s):  
Ion Transport ◽  
Absorptive Capacity ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Proximal Colon ◽  
High Rate ◽  
Transport Parameters ◽  
In Vitro Effects

Steroids are potent absorbagogues, increasing Na and fluid absorption in a variety of epithelia. This study characterizes the in vitro effects of pharmacological doses of gluco- and mineralocorticoids on transport parameters of rabbit proximal and distal colon. Treatment with methylprednisolone (MP, 40 mg im for 2 days) and desoxycortone acetate (DOCA, 12.5 mg im for 3 days) resulted in a significant increase in short-circuit current (Isc) in distal colon, suggesting an increase in basal Na absorption. Amiloride (10(-4) M) caused a significantly negative Isc in MP-treated tissue, demonstrating a steroid-induced, amiloride-insensitive electrogenic ion transport in distal colon. The effect of two absorbagogues, impermeant anions (SO4-Ringer) and amphotericin, were compared in control and steroid-treated distal colon. In controls, both absorbagogues increased Isc. Impermeant anions caused a rise in Isc in both MP and DOCA tissues, suggesting that the high rate of basal Na absorption had not caused a saturation of the Na pump. The steroid-treated colons, however, did not consistently respond to amphotericin. Amiloride inhibited the entire Isc in MP-treated distal colon that had been exposed to amphotericin; this suggested that amphotericin had not exerted its characteristic effect on the apical membrane of steroid-treated colon. In proximal colon, steroids did not alter basal rates of transport; however, epinephrine-induced Na-Cl absorption was significantly greater in MP-treated vs control (P less than 0.005). Steroids increase the absorptive capacity of both proximal and distal colon for Na, while increasing basal Na absorption only in the distal colon.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioenergetics and mechanical actuation analysis with membrane transport experiments for use in biomimetic nastic structures

2006 ◽  
Vol 21 (8) ◽  
pp. 2058-2067 ◽  
Author(s):  
Luke Matthews ◽  
Vishnu Baba Sundaresan ◽  
Victor Giurgiutiu ◽  
Donald J. Leo
Keyword(s):  
Active Transport ◽  
Transport Process ◽  
Fluid Transport ◽  
Shape Change ◽  
Bilayer Membrane ◽  
Ion Channel Proteins ◽  
Polymeric Plate ◽  
Active Transport Process ◽  
Controllable Deformation ◽  
Pressure Changes

Nastic structures are synthetic constructs capable of controllable deformation and shape change similar to plant motility, designed to imitate the biological process of nastic movement found in plants. This paper considers the mechanics and bioenergetics of a prototype nastic structure system consisting of an array of cylindrical microhydraulic actuators embedded in a polymeric plate. Non-uniform expansion/contraction of the actuators in the array may yield an overall shape change resulting in structural morphing. Actuator expansion/contraction is achieved through pressure changes produced by active transport across a bilayer membrane. The active transport process relies on ion-channel proteins that pump sucrose and water molecules across a plasma membrane against the pressure gradient. The energy required by this process is supplied by the hydrolysis of adenosine triphosphate. After reviewing the biochemistry and bioenergetics of the active transport process, the paper presents an analysis of the microhydraulic actuator mechanics predicting the resulting displacement and output energy. Experimental demonstration of fluid transport through a protein transporter follows this discussion. The bilayer membrane is formed from 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt), 1-Palmitoyl-2-Oleoyl-sn-Glycero- 3-Phosphoethanolamine lipids to support the AtSUT4 H+-sucrose cotransporter.

Functional development of active sugar transport in the chick intestine

1964 ◽  
Vol 207 (1) ◽  
pp. 37-41 ◽  
Author(s):  
Phyllis Holt Bogner ◽  
I. Ann Haines
Keyword(s):  
Active Transport ◽  
Age Groups ◽  
Sugar Transport ◽  
Mutual Inhibition ◽  
Tissue Water ◽  
Functional Development ◽  
Active Transport Process ◽  
Accumulation Method

The intestinal sugar transport function of late embryos and young chicks was studied by means of the tissue-accumulation method. Penetration of intestinal slices by sorbose was minimal in all age groups, ranging between 0.2 and 6.0 µmoles/g dry wt. The ratio of sorbose concentration in tissue water to that in the final medium (T/M) never exceeded 0.3. Galactose uptake by embryonic intestine was comparable to that for sorbose. In contrast, 0-day-old slices accumulated 29 µmoles galactose/g dry wt. which gave a T/M of 3.7. Maximal concentrative power was exhibited by 2-day-old slices which accumulated 38 µmoles galactose/g dry wt., resulting in a T/M of 7.4. Mutual inhibition of active transport between glucose and galactose was observed in 2-day-old slices. In intact chicks alimentary absorption rates of these two sugars rose sharply and to about the same extent between 0 and 2 days of age. Hence both in vitro and in vivo evidence suggests that an active transport process for sugars becomes functional in the chick intestine during the hatching period.

EQUILIBRATION OF SUCCINATE SOLUTIONS WITH ADAPTED AND UNADAPTED AZOTOBACTER CELLS

1954 ◽  
Vol 1 (1) ◽  
pp. 36-44 ◽  
Author(s):  
Anna Maria Williams ◽  
P. W. Wilson
Keyword(s):  
Active Transport ◽  
Transport Process ◽  
External Solution ◽  
Intracellular Water ◽  
Permeability Changes ◽  
Rapid Diffusion ◽  
Active Transport Process

Sucrose-grown (unadapted) and succinate-grown (adapted) cells were mixed with various concentrations of succinate at 3 °C. under air and at 30 °C. under helium. The amount of succinate removed from the external solution by the cells was proportional to the concentration of succinate and did not differ significantly with the two types of cells. Although the data did not differentiate between equilibration with intracellular water and mere adsorption, they indicate that no change has occurred in the surface of the adapted cells to allow a more rapid diffusion of succinate across the osmotic barrier under nonmetabolic conditions. So far as can be determined by using masses of cells, any "permeability" changes during adaptation of the azotobacter cells to succinate must be connected with an active transport process associated with metabolism.

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