Proline transport and oxidation in short-circuited locust rectum: effect of cAMP

1984 ◽  
Vol 62 (9) ◽  
pp. 1732-1736 ◽  
Author(s):  
J. Spring ◽  
J. E. Phillips
Keyword(s):  
Amino Acid ◽  
Active Transport ◽  
Energy Supply ◽  
Short Circuit ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Metabolic Substrate ◽  
Proline Transport

Proline absorption from the lumen is the main source of substrate supporting electrogenic Cl− transport and short-circuit current (Isc) in locust rectum. Since cAMP stimulates chloride-dependent Isc by up to 10-fold, we investigated whether this stimulant also increases active transport of the major metabolic substrate proline. A large 40:1 flux ratio of [14C]proline under short-circuited conditions confirmed that net absorption of this amino acid is by active transport. Unexpectedly, cAMP caused a 40% decrease in net transepithelial flux of proline. A 45% increase in the amount of proline oxidized to 14CO2 could account for only 10% of this decrease in proline flux, suggesting that increased Cl− transport after stimulation may competitively reduce the energy supply for proline transport.

scholarly journals IONIC TRANSFER ACROSS THE ISOLATED FROG LARGE INTESTINE

1959 ◽  
Vol 42 (3) ◽  
pp. 461-473 ◽  
Author(s):  
I. L. Cooperstein ◽  
C. Adrian M. Hogben
Keyword(s):  
Active Transport ◽  
Large Intestine ◽  
Short Circuit ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Considerable Proportion ◽  
Ionic Transfer ◽  
Serosal Surface ◽  
Net Flux ◽  
Unidirectional Fluxes

The unidirectional fluxes of sodium, chloride, and of the bicarbonate and CO2 pair were determined across the isolated large intestine of the bullfrog, Rana catesbiana. The isolated large intestine of the frog is characterized by a mean transmembrane potential of 45 mv., serosal surface positive with respect to mucosal. The unidirectional sodium flux from mucosal to serosal surface was found to be equal to the short-circuit current, thus the net flux was less than the simultaneous short-circuit current. This discrepancy between active sodium transport and short-circuit current can be attributed to the active transport of cation in the same direction as sodium and/or the active transport of anion in the opposite direction. The unidirectional fluxes of chloride and the bicarbonate and CO2 pair revealed no evidence for active transport of either anion. A quantitative study of chloride fluxes at 45 mv. revealed a flux ratio of 1.8 which is considerably less than a ratio of 6 expected for free passive diffusion. It was concluded that a considerable proportion of the isotopic transfer of chloride could be attributed to "exchange diffusion." Study of the electrical properties of the isolated frog colon reveals that it can be treated as a simple D. C. resistance over the range of -20 to +95 mv.

Somatostatin-related peptides isolated from the eel gut: effects on ion and water absorption across the intestine of the seawater eel.

1994 ◽  
Vol 188 (1) ◽  
pp. 205-216 ◽  
Author(s):  
T Uesaka ◽  
K Yano ◽  
M Yamasaki ◽  
K Nagashima ◽  
M Ando
Keyword(s):  
Amino Acid ◽  
Water Absorption ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Neuronal Firing ◽  
European Eel ◽  
Amino Acid Residues ◽  
Stimulatory Action ◽  
Adrenergic Antagonist ◽  
Large Peptide

Four somatostatin-related peptides were isolated from eel guts. Two of them were the same as eel SS-25II (eSS-25II) and eel SS-25I (eSS-25I) isolated from European eel pancreas. The remaining two peptides were C-terminal tetradecapeptides (eSS-14II and eSS-14I) of eSS-25II and eSS-25I, respectively. These four peptides all enhanced the serosa-negative transepithelial potential difference and short-circuit current across the seawater eel intestine after pretreatment with isobutylmethylxanthine, serotonin (5-HT) and methacholine, an agonist of acetylcholine (ACh). Among these peptides, eSS-25II was the most potent enhancer, followed by eSS-25I and eSS-14II. Since the large peptide (eSS-25II) acts at a lower concentration than the small somatostatin (eSS-14II), the 11 N-terminal amino acid residues seem to potentiate somatostatin action in the eel intestine. In contrast, eSS-14II was more potent than mammalian SS-14, indicating that the three amino acid residues (Tyr18, Gly21, Pro22) in the C-terminal portion also contribute to the potency of somatostatin. Endogenous somatostatin (eSS-25II) activated net Na+, Cl- and water fluxes across the seawater eel intestine. This stimulatory action was not inhibited by tetrodotoxin or yohimbine, an adrenergic antagonist, indicating that eSS-25II does not act through neuronal firing or through catecholamine release. Thus, eel somatostatins may act directly on the enterocytes, but on a distinct receptor from that for adrenaline, to antagonize the inhibition of NaCl and water absorption by 5-HT and ACh in the seawater eel intestine.

An electrogenic amino acid transporter in the apical membrane of cultured human bronchial epithelial cells

1998 ◽  
Vol 275 (5) ◽  
pp. L917-L923 ◽  
Author(s):  
Luis J. V. Galietta ◽  
Luciana Musante ◽  
Leila Romio ◽  
Ubaldo Caruso ◽  
Annarita Fantasia ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Amino Acid ◽  
Epithelial Cells ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Bronchial Epithelial Cells ◽  
Maximal Effect ◽  
Human Bronchial Epithelial Cells ◽  
Bronchial Epithelial

We performed Ussing chamber experiments on cultured human bronchial epithelial cells to look for the presence of electrogenic dibasic amino acid transport. Apical but not basolaterall-arginine (10–1,000 μM) increased the short-circuit current. Maximal effect and EC50were ∼3.5 μA/cm2and 80 μM, respectively, in cells from normal subjects and cystic fibrosis patients. The involvement of nitric oxide was ruled out because a nitric oxide synthase inhibitor ( NG-nitro-l-arginine methyl ester) did not decrease the arginine-dependent current. Apicall-lysine,l-alanine, andl-proline, but not aspartic acid, were also effective in increasing the short-circuit current, with EC50values ranging from 26 to 971 μM. Experiments performed with radiolabeled arginine demonstrated the presence of an Na+-dependent concentrative transporter on the apical membrane of bronchial cells. This transporter could be important in vivo to maintain a low amino acid concentration in the fluid covering the airway surface.

Alkaline secretion by amphibian duodenum. II. Short-circuit current and Na+ and Cl- fluxes

1981 ◽  
Vol 240 (6) ◽  
pp. G472-G479 ◽  
Author(s):  
J. N. Simson ◽  
A. Merhav ◽  
W. Silen
Keyword(s):  
Regression Analysis ◽  
Anion Exchange ◽  
Short Circuit ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Disulfonic Acid ◽  
Coupled Transport ◽  
Ratio Equation ◽  
Alkaline Secretion ◽  
Net Fluxes

The relations among alkaline secretion, short-circuit current (Isc), and fluxes of Na+ and Cl- are examined. The Isc (1.15 +/- 0.03 microeq.cm-2.h-1) was significantly greater than the rate of alkaline secretion (1.02 +/- 0.02 microeq.cm-2.h-1). Regression analysis (n = 300) showed a highly significant correlation between alkaline secretion and Isc and indicated a residual Isc of 0.26 microeq.cm-2.h-1. In the absence of HCO3-, there was a residual Isc of 0.25 +/- 0.04 microeq.cm-2.h-1. This residual Isc is accounted for by an observed net Na+ absorption of 0.28 +/- 0.04 microeq.cm-2.h-1. Fluxes of Na+ fail to fit the flux-ratio equation and were not significantly affected by 2 X 10(-6) M ouabain, 5 X 10(-5) M amiloride, or anoxia but were significantly reduced by 2,4,6-triaminopyrimidine. The net Cl- flux was not significantly different from zero. Cl- fluxes conform to the flux-ratio equation and were reduced by anoxia or 2,4,6-triaminopyrimidine but were not affected by 4-acetamido-4'-isothiocynostilbene-2,2'-disulfonic acid (SITS). Anoxia or ouabain significantly inhibited alkaline secretion and Isc without affecting net fluxes of Na+ or Cl-, whereas amiloride or SITS had no effect on any of these parameters. There is no NaCl-coupled transport nor anion exchange, but solute-coupled Na+ absorption is demonstrated. We conclude that alkaline secretion by the duodenum involves a transcellular, energy-requiring, Na+-dependent, ouabain-sensitive, electrogenic mechanism that accounts for at least 80% of the Isc. Net Na+ absorption accounts for the residual Isc. Movements of Cl- are passive, do not contribute to Isc, and are not involved in the mechanism of alkaline secretion. Two hypothetical models of transcellular alkaline secretion are proposed.

Ion transport across rumen and omasum epithelium

1971 ◽  
Vol 262 (842) ◽  
pp. 301-305 ◽  
Keyword(s):  
Active Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Chloride Ions ◽  
Rumen Epithelium ◽  
Sodium Flux ◽  
Sodium System ◽  
Chloride Pump ◽  
Net Flux ◽  
Cattle And Sheep

The interior of the rumen in cattle and sheep is normally maintained at a potential of about — 40 mV relative to the blood. This potential depends primarily on the occurrence of an active transport of sodium from rumen to blood, since the potential, short-circuit current and the net sodium flux are simultaneously abolished by anoxia, ouabain and removal of sodium from the bathing solutions. There is an appreciable net flux of potassium from blood to rumen. There is also a substantial active transport of chloride in the same direction as sodium and it can be reduced by treatment with acetazolamide without affecting the potential or the sodium system. Nevertheless, sodium transport is reduced by the removal of chloride ions. Omasum epithelium is similar to rumen epithelium. However, the chloride pump appears to work in both directions in this tissue. Short-circuited omasum epithelium can also transport magnesium from omasum to blood.

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.

Electrical and transport characteristics of skin of larval Rana catesbeiana

1979 ◽  
Vol 237 (1) ◽  
pp. R74-R79 ◽  
Author(s):  
T. C. Cox ◽  
R. H. Alvarado
Keyword(s):  
Rana Catesbeiana ◽  
Short Circuit ◽  
Electrical Potential ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Open Circuit ◽  
Shunt Resistance ◽  
Ion Substitution ◽  
Adult Skin

Carefully dissected, mounted, and bathed with Ringer solution, the larval bullfrog skin has a resistance of about 9,000 omega.cm2 and a stable transepithelial electrical potential of about 20 mV (inside +). A short-circuit current of about 2 microA.cm-2 is generated that is comparable in magnitude to the net inward flux of Na+. At open circuit the flux ratio equation for Na+ is not satisfied. Larval skin is less sensitive to ouabain, amiloride, and ADH than adult skin. The current-voltage (C-V) relationship across the preparation is not linear; there are distinct breaks in both the hyperpolarizing and hypopolarizing regions. The former break, at about +130 mV, corresponds with a break observed in adult skin that corresponds with ENa. The shunt resistance (RS) and active pathway resistance (RA) were estimated by C-V curve analysis and by ion substitution. The two methods yielded comparable values with RS about 11 k omega.cm2 and RA about 62 k omega.cm2. It is suggested that transport is limited by the number of entry sites for sodium at the apical border of transport cells.

In vitro studies of sodium transport across the lower intestine of a desert parrot

1980 ◽  
Vol 239 (3) ◽  
pp. R285-R290
Author(s):  
E. Skadhauge ◽  
T. J. Dawson
Keyword(s):  
Short Circuit ◽  
Electrical Potential ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Na Transport ◽  
Salt Loading ◽  
Ussing Chambers ◽  
Lower Intestine

The lower intestine (coprodeum and colon) of the Australian parrot, the galah, was mounted in Ussing chambers. Short-circuit current (SCC), electrical potential difference (PD), and unidirectional fluxes of Na and Cl were measured in birds that were fed mixed seeds or were NaCl loaded. The net Na transport of both coprodeum and colon was nearly equal to the SCC, and the flux ratio for Cl was unity. In birds which received mixed seeds, average coprodeal Na transport was 7.8 mu eq . cm-2 . h-1, and PD was 19 mV. The Km for Na was 5.7 meq/l. In colon, Na transport was reduced by 67% and PD by 70%. The ratio between unidirectional Na and Cl fluxes in the serosa-mucosa direction was 0.7. Salt loading suppressed coprodeal, but increased colonic Na transport. The coprodeal and colonic SCC and NA transport of birds receiving mixed seeds were inhibited by amiloride on the mucosal side. Colonic SCC of NaCl-loaded birds was only slightly reduced by amiloride (by 17%), but stimulated by amino acids (by 18%).

Amphotericin B-induced active transport of K+ and the Na+-K+ flux ratio in frog corneal epithelium

1984 ◽  
Vol 247 (5) ◽  
pp. C454-C461 ◽  
Author(s):  
O. A. Candia ◽  
P. S. Reinach ◽  
L. Alvarez
Keyword(s):  
Amphotericin B ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Bathing Solution ◽  
Experimental Conditions ◽  
Corneal Epithelial ◽  
K Concentration ◽  
K Transport

Transepithelial unidirectional K+ fluxes across the isolated frog cornea were primarily paracellular and proportional to the K+ concentration in the bathing solution (from 2.5 to 25 mM). The net K+ flux was not different from zero. Amphotericin B (10(-5) M) elicited a large and sustained net K+ transport from the stroma- to the tear-side bathing solution of about 10 microA/cm2. Concomitantly, a net Na+ transport occurs in the opposite direction with a short-circuit current from tear to stroma of about 25 microA/cm2. The net K+ transport exhibited saturation, increasing only 35% when the K+ concentration in the bathing solution was augmented five times. Cellular K+ content measured analytically after scraping off the epithelium was reduced by amphotericin B from 0.56 to 0.10 mueq. The amphotericin B-induced K+ transport was inhibited by ouabain and low Na+ (5 mM) in the tear-side solution. Paracellular permeability determined with mannitol or estimated from the tear-to-stroma K+ flux increased four times with amphotericin B. From the net K+ transport and the short-circuit current, the Na+-K+ flux ratio was calculated and found to vary between 2.2 and possibly as high as 5.5 among corneas in the same experimental conditions. The Na+-K+ flux ratio determined in the same cornea decreased as the K+ concentration in the bathing solution increased. Such variability suggests that in corneal epithelial cells the Na+-K+ coupling ratio is sensitive to changes in the electrochemical gradient across the basolateral membrane of the cell.

Active Transport of Potassium and Oxygen Consumption in the Isolated Midgut of Hyalophora Cecropia

1967 ◽  
Vol 46 (2) ◽  
pp. 235-248
Author(s):  
W. R. HARVEY ◽  
J. A. HASKELL ◽  
K. ZERAHN
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Uptake ◽  
Active Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Na Transport ◽  
Maximum Value ◽  
Flux Measurements ◽  
Hyalophora Cecropia ◽  
K Transport

1. Flux measurements with 42K reveal that in the isolated midgut of Hyalophora cecropia 90 to 100 % of the short-circuit current is carried by the active transport of potassium from the blood-side to the lumen. 2. When K-transport is strongly depressed, either by withholding potassium from the blood side or by imposing a large positive potential on the lumen, the oxygen uptake of the isolated gut remains virtually unchanged. If the K-transport were to be energized by the negligible increase in oxygen uptake about 40 µ-equiv. of potassium would have to be transported for every µ-equiv. of extra oxygen taken up. This ratio of K-transport to oxygen uptake is thermodynamically impossible. 3. The ratio of potassium transported to total oxygen consumed when the midgut is bathed with 32 mM potassium on both sides is about 1.3 at temperatures of 25° and 15° C. The ratio must be smaller at lower potassium concentrations and is 2.0 at 73.5 mM-K, which may be approaching the maximum value. 4. Although the oxygen uptake is independent of the K-transport, the reverse is not true. There is a close dependency of K-transport on oxygen consumption. 5. K-transport by the midgut contrasts with Na-transport by the frog skin because Na-transport stimulates oxidative metabolism whereas K-transport does not. Evidently the coupling of transport to energy supply is different in the two systems.

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