Chloride balance in Rana pipiens

1975 ◽  
Vol 229 (3) ◽  
pp. 861-868 ◽  
Author(s):  
RH Alvarado ◽  
AM Poole ◽  
TL Mullen
Keyword(s):  
Steady State ◽  
Active Transport ◽  
Transport System ◽  
Rana Pipiens ◽  
Chloride Transport ◽  
Choline Chloride ◽  
Passive Permeability ◽  
Exchange Diffusion ◽  
Active Uptake ◽  
Saturation Kinetics

Frogs kept in dilute solutions of Cl- maintain a steady state with respect to this ion. Chloride is exchanged at a rate of about 15 mumol 100 g-1 h-1 (47 nmol cm-2 h-1). Over 90% of the efflux is integumentary of which about 50% is diffusion of the total influx. The rest is carrier mediated, half of which is exchange diffusion and half active transport. The chloride transport system displays saturation kinetics and is inhibited by acetazolamide. Uptake of Cl- is not dependent on concomitant uptake of cations. Salt-depleted frogs accumulate Cl- from dilute KCl or choline chloride in exchange for an endogenous base, probably HCO-3. High bath concentrations of NaCl (greater than 5 mM) abolish the active uptake of Cl- and increase the passive permeability of the skin to Cl-.

Chloride transport across isolated skin of Rana pipiens

1975 ◽  
Vol 229 (3) ◽  
pp. 869-876 ◽  
Author(s):  
RH Alvarado ◽  
TH Dietz ◽  
TL Mullen
Keyword(s):  
Active Transport ◽  
Frog Skin ◽  
Rana Pipiens ◽  
Chloride Transport ◽  
Iodoacetic Acid ◽  
Temperature Sensitive ◽  
Na Transport ◽  
Exchange Diffusion ◽  
Paracellular Pathways ◽  
Unidirectional Fluxes

The influx of Cl- across isolated frog skin bathed on the outside by 0.8 mM NaCl is about 100 nmol cm-2 h-1, which is approximately twice the Cl- influx in intact animals. The influx consists of diffusion (1%), exchange diffusion (38%), and active transport (60%). About 80% of the influx is independent of Na+ in the outer bath and is also independent of concomitant inward movement of cations. Chloride is exchanged for anions, probably HCO-3. The Cl- transport system is saturable; Vmax is about 200 nmol cm-2 h-1, and Ks is about 0.7 mM Cl-. High external concentrations of NaCl increase unidirectional fluxes of Cl- and urea, indicating a change in paracellular pathways. Active transport of Cl- is temperature sensitive (Q10 equals 2.68) and is inhibited by cyanide, dinitrophenol, iodoacetic acid, iodide, thiocyanate, and acetazolamide. The Na-independent component of JClin was unaffected by amiloride, ouabain, or eserine, all of which inhibit Na+ transport.

Efflux of sodium from isolated toad bladder

1963 ◽  
Vol 205 (4) ◽  
pp. 718-722 ◽  
Author(s):  
Howard S. Frazier ◽  
Earle I. Hammer
Keyword(s):  
Diffusion Process ◽  
Active Transport ◽  
Mucosal Surface ◽  
Toad Bladder ◽  
Surface Replacement ◽  
Abrupt Increase ◽  
Exchange Diffusion ◽  
Serosal Surface ◽  
Saturation Kinetics ◽  
Stimulation Of

A method of simultaneously determining the rates of loss of Na24 across the mucosal and serosal surfaces of the isolated toad bladder is described. The addition of vasopressin to the serosal medium causes an abrupt increase in the efflux of Na24 across the mucosal boundary, with no significant change in the efflux across the serosal surface. Replacement of sodium in the mucosal medium with choline causes no change in the efflux of Na24 across either the mucosal or serosal surfaces. The results indicate that the stimulation of active transport of sodium across the bladder after vasopressin is the result solely of an increase in the permeability to sodium of the mucosal surface. Vasopressin does not act directly on the active transport step at the serosal surface. In addition, the saturation kinetics which describe the process of sodium entry at the mucosal boundary are not the result of an exchange diffusion process, and appear not to be due to a sodium-induced change in the permeability of this surface to sodium.

Transport of sodium and chloride by the isolated rumen epithelium

1964 ◽  
Vol 206 (5) ◽  
pp. 1099-1105 ◽  
Author(s):  
Charles E. Stevens
Keyword(s):  
Sodium Chloride ◽  
Active Transport ◽  
Chloride Transport ◽  
Short Circuit ◽  
Electrical Potential ◽  
Short Circuit Current ◽  
Exchange Diffusion ◽  
Rumen Epithelium ◽  
Tissue Resistance ◽  
Affected Tissue

Transepithelial electrical potential, short-circuit current, and resistance measurements were made under different conditions of tissue collection and maintenance. The collection procedure greatly affected tissue resistance and, since the magnitude of the current was relatively independent of the procedure, potential was affected to about the same degree. The highest and least variable resistances were recorded when the tissue was removed from the anesthetized cow and the epithelium carefully dissected free. Short-circuit current and net ion flux decreased with time but the decrease was relatively linear and sufficiently slow to allow their comparison. Rumen epithelium of both species demonstrated active transport of Na and Cl in the direction of lumen to blood. Calculation of partial Na conductances indicated that part of the sodium was transported by exchange diffusion or a sodium chloride transport system.

Adenosine uptake by the isolated epithelium of guinea pig jejunum

1977 ◽  
Vol 55 (5) ◽  
pp. 1033-1038 ◽  
Author(s):  
N. Kolassa ◽  
R. Stengg ◽  
K. Turnheim
Keyword(s):  
Guinea Pig ◽  
Transport System ◽  
Intestinal Epithelium ◽  
Initial Velocity ◽  
Transport Mechanism ◽  
Passive Diffusion ◽  
Passive Permeability ◽  
Adenosine Uptake ◽  
Saturation Kinetics ◽  
Pig Jejunum

The uptake of [8-14C]adenosine by the isolated epithelium of guinea pig jejunum was faster than that of inosine, hypoxanthine, or adenine. The initial velocity of adenosine uptake from both the luminal and the antiluminal side of the epithelium exhibited saturation kinetics. The apparent Km, V, and passive permeability of luminal adenosine uptake were all lower than the corresponding values of antiluminal uptake. p-Nitrobenzyl-thioguanosine inhibited adenosine uptake from both the luminal and the antiluminal side, whilst hexobendine decreased the uptake only from the antiluminal side of the epithelium. The results suggest that adenosine enters the intestinal epithelium by a carrier-mediated process in addition to passive diffusion. The antiluminal transport system for adenosine seems similar to that of other tissues with respect to hexobendine inhibition; the luminal transport mechanism, however, exhibits different properties, being insensitive to hexobendine.

scholarly journals The uptake of γ-aminobutyrate by organotypic cultures of chick spinal cord

1973 ◽  
Vol 134 (1) ◽  
pp. 27-32 ◽  
Author(s):  
G. Tunnicliff ◽  
Y. D. Cho ◽  
Natalie Blackwell ◽  
R. O. Martin ◽  
J. D. Wood
Keyword(s):  
Spinal Cord ◽  
Active Transport ◽  
Transport System ◽  
Nervous Tissue ◽  
Temperature Sensitive ◽  
Saturation Kinetics ◽  
The Central Nervous System ◽  
Uptake Process ◽  
Active Transport System ◽  
Chick Spinal Cord

1. Explants of spinal cord from 10-day chick embryos maintained for up to 16 days in culture rapidly accumulated γ-amino[3H]butyrate when incubated at 25°C or 36°C in a medium containing 50nm-γ-aminobutyrate. The mechanism of the uptake process has many of the properties of an active-transport system: it is Na+-dependent, temperature-sensitive, inhibited by ouabain, and displays saturation kinetics. The apparent Km for γ-aminobutyrate is 1.7×10−5m, and Vmax. is 33pmol/min per g. 2. The rate of accumulation of γ-amino[3H]butyrate in cultures between the ages of 3 and 16 days was remarkably constant and was not related to the morphological maturity of the spinal-cord explants. 3. The present demonstration in spinal-cord explants of an active transport system for γ-aminobutyrate, already established for non-cultured nervous tissue, means that nervous-tissue culture can provide a convenient model for studying uptake processes in the central nervous system.

Coupling between chloride absorption and base excretion in isolated skin of Rana esculenta

1978 ◽  
Vol 235 (1) ◽  
pp. F33-F39
Author(s):  
J. Ehrenfeld ◽  
F. Garcia-Romeu
Keyword(s):  
External Medium ◽  
Chloride Transport ◽  
Short Circuit ◽  
Choline Chloride ◽  
Chloride Concentration ◽  
External Solution ◽  
Rana Esculenta ◽  
Ringer Solution ◽  
Chloride Absorption ◽  
Saturation Kinetics

The net excretory fluxes of base (HCO3- or OH-) and the unidirectional fluxes of chloride were measured and their relationship examined in isolated frog skin maintained in open- or short-circuit (OC and SC) conditions. When the mucosal solution was a 2 mM choline chloride solution and the serosal solution a Ringer solution buffered with a HCO3-/CO2 mixture, the rate of base excretion was -105 +/- 10 in OC and -60 +/- 7 neq h-1 cm-2 in SC. A highly significant correlation was observed between the influx of chloride and the excretion of base. As a function of external chloride both these parameters followed saturation kinetics, Vmax being obtained for a chloride concentration below 2 mM. The removal of chloride in the external solution was followed by a 70 or 100% inhibition of base excretion in OC and SC conditions, respectively. Chloride transport is dependent on the presence of a HCO3-/CO2 mixture in the internal or the external medium. This transport, as well as base excretion, is inhibited to a considerable extent by removal of HCO3-/CO2 or by acetazolamide (10(-3) M). This investigation characterizes a saturable transport system in which chloride absorption and base excretion are coupled.

On the structural organization of biological pumps and channels

1984 ◽  
Vol 42 ◽  
pp. 138-141
Author(s):  
G. Zampighi ◽  
M. Kreman
Keyword(s):  
Active Transport ◽  
Transport System ◽  
Plasma Membranes ◽  
Transport Proteins ◽  
Molecular Organization ◽  
Passive Transport ◽  
Concentration Gradients ◽  
Cell Functions ◽  
Natural Concentration ◽  
Active Transport System

The plasma membranes of most animal cells contain transport proteins which function to provide passageways for the transported species across essentially impermeable lipid bilayers. The channel is a passive transport system which allows the movement of ions and low molecular weight molecules along their concentration gradients. The pump is an active transport system and can translocate cations against their natural concentration gradients. The actions and interplay of these two kinds of transport proteins control crucial cell functions such as active transport, excitability and cell communication. In this paper, we will describe and compare several features of the molecular organization of pumps and channels. As an example of an active transport system, we will discuss the structure of the sodium and potassium ion-activated triphosphatase [(Na+ +K+)-ATPase] and as an example of a passive transport system, the communicating channel of gap junctions and lens junctions.

scholarly journals Equilibrium properties of a voltage-dependent junctional conductance.

1981 ◽  
Vol 77 (1) ◽  
pp. 77-93 ◽  
Author(s):  
D C Spray ◽  
A L Harris ◽  
M V Bennett
Keyword(s):  
Steady State ◽  
Rana Pipiens ◽  
Energy Difference ◽  
Ambystoma Mexicanum ◽  
Voltage Sensitivity ◽  
Junctional Conductance ◽  
Voltage Dependent ◽  
Accumulation Mechanism ◽  
Conductance Changes ◽  
A Current

The conductance of junctions between amphibian blastomeres is strongly voltage dependent. Isolated pairs of blastomeres from embryos of Ambystoma mexicanum, Xenopus laevis, and Rana pipiens were voltage clamped, and junctional current was measured during transjunctional voltage steps. The steady-state junctional conductance decreases as a steep function of transjunctional voltage of either polarity. A voltage-insensitive conductance less than 5% of the maximum remains at large transjunctional voltages. Equal transjunctional voltages of opposite polarities produce equal conductance changes. The conductance is half maximal at a transjunctional voltage of approximately 15 mV. The junctional conductance is insensitive to the potential between the inside and outside of the cells. The changes in steady-state junctional conductance may be accurately modeled for voltages of each polarity as arising from a reversible two-state system in which voltage linearly affects the energy difference between states. The voltage sensitivity can be accounted for by the movement of about six electron charges through the transjunctional voltage. The changes in junctional conductance are not consistent with a current-controlled or ionic accumulation mechanism. We propose that the intramembrane particles that comprise gap junctions in early amphibian embryos are voltage-sensitive channels.

scholarly journals Inhibition of Amino Acid Transport in Rabbit Intestine by p-Chloromercuriphenyl Sulfonic Acid

1973 ◽  
Vol 62 (2) ◽  
pp. 131-146 ◽  
Author(s):  
John F. Schaeffer ◽  
Robert L. Preston ◽  
Peter F. Curran
Keyword(s):  
Transport System ◽  
Conformational Changes ◽  
Marked Reduction ◽  
Sulfhydryl Group ◽  
Major Effect ◽  
Acid Transport ◽  
Michaelis Constant ◽  
Saturation Kinetics ◽  
Rabbit Intestine ◽  
Transport Site

Influx of phenylalanine across the brush border of rabbit intestine is markedly reduced by treatment with 5 mM p-chloromercuriphenyl sulfonate (PCMBS). The effect is rapidly and completely reversed by dithiothreitol. Phenylalanine influx into PCMBS-treated tissue can be competitively inhibited by other neutral amino acids and follows saturation kinetics. PCMBS causes an increase in the apparent Michaelis constant from the value observed in control tissue but does not alter the maximal influx significantly. Treatment of the tissue with PCMBS leads to a significant reduction in the Na-sensitivity of the transport, and a number of results indicate that the major effect of the reagent is to cause a marked reduction in the affinity of the transport system for Na. The transport system can be partially protected against reaction with PCMBS by phenylalanine and tryptophan but not by methionine or norleucine. The results suggest that PCMBS reacts with a sulfhydryl group in the region of the transport site and may alter conformational changes associated with the binding of substrates.

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