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.

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.

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.

Active transport of calcium across the isolated midgut of Hyalophora cecropia

1976 ◽  
Vol 65 (2) ◽  
pp. 347-360
Author(s):  
J. L. Wood ◽  
W. R. Harvey
Keyword(s):  
Calcium Influx ◽  
Short Circuit ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Ca Transport ◽  
High Calcium ◽  
Wet Weight ◽  
Net Flux ◽  
Kinetics Of

1. The net flux of 45Ca from lumen to blood side across the isolated and short-circuited Cecropia midgut was 1–9 +/− 0–2 muequiv. cm-2h-1 in 8 mM Ca and the flux ratio was as high as 56 to 1. 2. The calcium influx was depressed by anoxia; 73% after 30 min. 3. The kinetics of Ca transport were anomalous; the apparent Km varied with Ca concentration from less than 0–2 to greater than 5–6 mM Ca and the apparent Vmax varied from less than 1–3 to greater than 3-3 muequiv. cm-2h-1. 4. The calcium influx showed a delay before the tracer steady state was attained, indicating the existence in the transport route of a calcium pool equivalent to 5–7 muequiv/g. wet weight of midgut tissue. 5 High calcium (16 mM) depressed the short-circuit current and potassium transport from blood to lumen side across the midgut. 6. Calcium depressed magnesium transport, from lumen to blood side across the midgut, and magnesium depressed the calcium transport. 7. Ca transport by the midgut does not regulate the Ca level in the haemolymph in vivo; it merely aids the diffusion of calcium down its electrochemical gradient. However, Ca transport may assist the uptake of the nutrients from the midgut contents.

Effects of calcium removal on bullfrog gastric mucosa

1963 ◽  
Vol 205 (4) ◽  
pp. 631-637 ◽  
Author(s):  
John G. Forte ◽  
Alan H. Nauss
Keyword(s):  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potential Difference ◽  
Permeability Changes ◽  
Apparent Decrease ◽  
Net Flux ◽  
Ph Stat ◽  
Unidirectional Fluxes ◽  
Stat Method

Removal of calcium from isolated bullfrog gastric mucosae by serial washings in calcium-free solutions or by the addition of EDTA or citrate caused a fall in transmucosal potential difference, a rise in the mucosal conductance, and an apparent decrease in the rate of acid secretion as measured by the pH stat method. Unless the potential difference fell to values very nearly zero the short-circuit current was not significantly decreased. Unidirectional fluxes of chloride in both directions across the mucosa were increased by EDTA, but the net flux, or actively transported chloride, was not significantly altered. This suggests that the removal of calcium by these methods does not interfere with active chloride transport. The increased movement of sodium and sucrose across the mucosa after EDTA suggests that a large part of the permeability change is occurring at the spaces between cells. Because of the large permeability changes accompanying removal of calcium it is postulated that the process of H+ production is not directly inhibited.

Ion transport in isolated cornea of the rabbit

1965 ◽  
Vol 209 (6) ◽  
pp. 1311-1316 ◽  
Author(s):  
K. Green
Keyword(s):  
Ion Transport ◽  
Active Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Ringer Solution ◽  
Initial Value ◽  
Rabbit Cornea ◽  
Flux Measurements ◽  
Net Flux ◽  
Normal Ringer

When the isolated rabbit cornea is bathed with well-stirred normal Ringer solution, only a low potential difference (PD) exists across the tissue; the initial value of 2 mv rises to 6 mv (endothelium positive) 1 hr after excision from the animal. In sodium-free Ringer solution the PD becomes negative before becoming negligible, while in chloride-free Ringer the PD rises to triple the value in normal Ringer. Flux measurements of sodium 22 show that there is an initial inequality between the net flux and the measured short-circuit current (SCC), the values of which become equal 1 hr after removal of the cornea from the animal Flux measurements of chloride 36 during this 1st hr indicate an active transport of chloride inward across the cornea, but after 1 hr the fluxes are equal in each direction. The differences of the net currents generated by the sodium and chloride transports equal the measured SCC, and the two transports have been shown to be able to exist independently.

Active transport of magnesium across the isolated midgut of Hyalophora cecropia

1975 ◽  
Vol 63 (2) ◽  
pp. 313-320
Author(s):  
J. L. Wood ◽  
A. M. Jungreis ◽  
W. R. Harvey
Keyword(s):  
Steady State ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Potassium Transport ◽  
Magnesium Concentration ◽  
Magnesium Transport ◽  
Wet Weight ◽  
Net Flux ◽  
Burk Plot

1. The 28Mg-measured net flux of magnesium from lumen-side to haemolymph-side of the isolated and short-circuited midgut was 1.97 +/− 0.28 mu-equiv cm(−2) /(−1) in 8 mM-Mg2+. 2. The magnesium-influx shows a delay before the tracer steady-state is attained, indicating the existence of a magnesium-transport pool equivalent to 6.7 mu-equiv/g wet weight of midgut tissue. 3. Magnesium depresses the short-circuit current produced the midgut but not the potassium transport, the depression being equal to the rate of magnesium transport. 4. Magnesium transport yields a linear Lineweaver-Burk plot with an apparent Km of 34 mM-Mg2+ and an apparent Vmax of 14.9 mu-equiv cm(−1) /(−1). 5. Magnesium is actively transported across the midgut and contributes to the regulation of the haemolymph magnesium concentration in vivo.

Suppression of gastric acid secretion by furosemide in isolated gastric mucosa of guinea pig

1980 ◽  
Vol 239 (6) ◽  
pp. G532-G535 ◽  
Author(s):  
A. Ayalon ◽  
A. Corcia ◽  
G. Klemperer ◽  
S. R. Caplan
Keyword(s):  
Guinea Pig ◽  
Acid Secretion ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Electrical Conductance ◽  
Short Circuit Current ◽  
Cl Transport ◽  
Consequent Reduction ◽  
Net Flux ◽  
Mucosal Side

The effect of furosemide on acid secretion and Cl- transport was studied in isolated fundic mucosa of the guinea pig. Furosemide (10(-3) M), applied to the serosal side produced an immediate effect on the short-circuit current (Isc), lowering it by 47 +/- 2%. Potential difference decreased by 29 +/- 3%, electrical conductance by 18 +/- 4%, acid secretion by 38 +/- 1%, and net flux of Cl- from serosal-to-mucosal side by 37%. Application of the drug to the mucosal side produced similar effects on acid secretion and on the electrical parameters. It is suggested that furosemide blocks the entrance of Cl-, by the Na+--Cl- cotransport mechanism, through the basolateral membrane of the secreting cell. The consequent reduction in electrogenic Cl- transport would cause Isc and acid secretion to decrease. A reduction of Cl- conductance of the apical membrane, upon mucosal application of the drug, would cause similar effects on acid secretion and Cl- transport.

Aspects of electrolyte transport across isolated dog retinal pigment epithelium

1986 ◽  
Vol 250 (5) ◽  
pp. F781-F784 ◽  
Author(s):  
S. Tsuboi ◽  
R. Manabe ◽  
S. Iizuka
Keyword(s):  
Retinal Pigment Epithelium ◽  
Apical Membrane ◽  
Short Circuit ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Short Circuit Current ◽  
Bathing Solution ◽  
Apical Side ◽  
Net Flux ◽  
Net Fluxes

Transport of Na and Cl across the isolated dog retinal pigment epithelium (RPE) choroid was investigated. Under the short-circuit condition, a net Na flux was observed from choroid to retina and a net Cl flux was determined in the opposite direction. The current created by the net flux of these two ions was larger than the short-circuit current (SCC). Addition of 10(-5) M ouabain to the apical side inhibited net fluxes of both Na and Cl, whereas it reduced the SCC 84%. Addition of 10(-4) M furosemide to the apical side inhibited net Cl flux but had no effect on the net Na transport. The 10(-4) M furosemide reduced the SCC 38%. These drugs had no effect when applied to the basal side. Thus the transport of both Na and Cl depends on the Na-K-ATPase in the apical membrane of the dog RPE. A furosemide-sensitive neutral carrier at the apical membrane is suggested for the transport of Cl. Replacement of HCO3 with SO4 in the bathing solution caused an increase in the SCC, indicating the choroid-to-retina movement of HCO3 across the short-circuited dog RPE choroid.

Action of adenosine on chloride active transport of isolated frog cornea

1979 ◽  
Vol 237 (2) ◽  
pp. F121-F127
Author(s):  
B. S. Spinowitz ◽  
J. A. Zadunaisky
Keyword(s):  
Rana Catesbeiana ◽  
Chloride Transport ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Adenyl Cyclase ◽  
Naturally Occurring ◽  
Chloride Pump ◽  
Net Flux ◽  
The One ◽  
Sustained Increase

Addition of adenosine (10–7 to 10–4 M) to the tear side of isolated corneas (Rana catesbeiana) produced a rapid, sustained increase in short-circuit current, potential difference, and radioisotopic chloride net flux. The increased net chloride flux accounted for the increased short-circuit current. Adenosine, a known activator of adenyl cyclase in other tissues, exerted its effects on chloride transport through a receptor different from the one described for epinephrine and prostaglandins in the corneal epithelium. Propranolol inhibited the epinephrine response but not the adenosine effect. Dipolyphloretin phosphate inhibited prostaglandin responses but did not affect the adenosine stimulation of chloride transport. Adenine and/or ribose, parts of the adenosine molecule, had no stimulatory effect, but 5'-AMP had a partial effect.The activation of the chloride pump with DBcAMP blocked the response to adenosine. Adenosine interacted with the effects of theophylline. Adenosine, a naturally occurring molecule, stimulated chloride transport by activation of adenyl cyclase through a separate membrane receptor in the corneal eqithelium.

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.

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