H. Albus

The electrophysiological characteristics of glucose absorption of the goldfish intestine as compared to mammalian intestines.

Abstract o 1. A new experimental set-up and procedure are described for the measurement of some electrophysiological properties of the isolated goldfish intestine ( Carassius auratus ). 2. With this apparatus it is possible to perform experiments over a 3 hr period without deterioration of the tissues structure. 3. The glucose-evoked potential (GEP) is probably the result of a rheogenic process as no change in the epithelial resistance occurred with or without glucose, mannitol or phlorizin in the mucosal solution. 4. The apparent K m for the GEP is 4 mM. 50% inhibition of the GEP was determined at a phlorizin concentration of 10 −5 M; while 10 −5 M ouabain caused an inhibition of 85%. These results are comparable with those given in the literature for mammalian intestine.

A mechanistic explanation of the effect of potassium on goldfish intestinal transport

Partial replacement of sodium by potassium or rubidium in the solution used to perfuse isolated intestinal segments of goldfish causes an increase in transmural electrical resistance. Serosal replacements have a stronger effect than mucosal replacements.A 70% inhibition of the glucose-evoked transmural electrical current is brought about by serosal replacement of 40 mM sodium by potassium. Transmural mucosal to serosal flux of 3-O-methyl-D-glucose is also strongly inhibited by serosal potassium. These inhibitory effects of potassium do not occur when the intestinal mucosa is stripped free from the intestinal muscular layers. It is concluded that potassium-induced muscular contractures cause a decrease in transport area by pressing the mucosal folds closer against each other.Certain effects of high potassium concentrations that have been reported in mammalian intestinal preparations may involve a similar mechanism.

Effects of glucose and ouabain on transepithelial electrical resistance and cell volume in stripped and unstripped goldfish intestine

Abstract1.In goldfish intestine (perfused unstripped segments and mucosal strips) the serosal addition of ouabain (10\t-4 M) resulted in a vanishment of the transepithelial potential difference and in a continuous increase in transepithelial resistance.2.Incubation of mucosal strips with ouabain resulted in an increase in sodium content which was greater than the decrease in potassium content. The resulting increase in cation content was accompanied by an increase in chloride content and an increase in water content.3.Histological examination showed that exposure to ouabain resulted in a swelling of the epithelial layer as compared to the control situation.4.The ouabain induced resistance increase is greater in the presence of glucose, 3-OMG or fructose than in the presence of mannitol. Phlorizin (10\t-4 M) inhibits the extra resistance increase induced by mucosal glucose but is without effect on the fructose induced extra resistance increase.The initial velocity and the magnitude of the glucose induced extra resistance increase depends on the glucose concentration.5.The results suggest that in goldfish intestine ouabain induces cellular swelling with a concomitant collapse of the lateral intercellular spaces, which is the cause of the increased transepithelial resistance. The additional changes in resistance induced by sugars suggest that the cell membrane is more permeable to glucose, 3-OMG and fructose than to mannitol. The resulting changes in osmotically active material within the epithelial cell influence the cross-sectional area and consequently the conductivity of the paracellular shunt pathway. The hypothesis that these sugars do not induce a resistance change in the absence of ouabain is discussed.

Circuit analysis of membrane potentials changes due to electrogenic sodium-dependent sugar transport in goldfish intestinal epithelium

The effect of glucose on the electrical potential profile in the stripped goldfish intestine was measured and analyzed in terms of cell membrane electromotive forces.In substrate free conditions, the mucosal membrane potential difference ψmc averaged −54 mV, cell interior negative. The addition of 27.8 mMd-glucose to the mucosal side of the epithelium evoked a rapid depolarization (Δψmc = +11.5 mV) followed by a slower repolarization (Δψmc = −6.0 mV) to a new steady state value of −48 mV. The membrane resistance ratioRm/Rs averaged 0.99. During the depolarization phase it was reduced by 18%, returning to the pre-glucose value within 2.5 min. The transepithelial resistanceRms was 19.7 Ωcm2 and did not change.Addition of ouabain induced a depolarization of ψmc without significant change inRms orRm/Rs during the first 15 min. Application of glucose to the mucosal solution a few minutes after ouabain exposure resulted in a rapid depolarization of ψmc without repolarization. The glucose induced transepithelial potential change reached only about 60% of the original value. From the ouabain experiments the relative shunt conductance was calculated to be 95%. In mannitol conditionsRm=Rs=197 Ωcm2, while the shunt resistanceR1=20.7 Ωcm2.Assuming no large changes in the potential through the shunt pathway, the analysis of the changes in electromotive forces (EMF) at both cell borders yields the following values ΔEm=+23.7 mV and ΔEs=−17.4 mV.Analysis of the changes in the electromotive force across the mucosal membrane as a function of the glucose concentration revealed the presence of a Na+-dependent glucosetransport system composed of two saturating processes.

Changes in surgar transport and in electrophysiological characteristics of intestinal preparations of temperature-acclimated goldfish (Carassius auratus L.)

Summary1.Goldfish were acclimated to temperatures of 10°C and 30°C for at least 4 weeks.2.Fish acclimated to 10°C have longer intestines with larger mucosal folds than fish acclimated to 30°C.3.When fish acclimated to 10°C are compared with 30°C fish, the electrical resistance of intestinal mucosa, expressed in Ωcm2 of serosal area, from 10°C-acclimated fish is higher. However when related to mucosal area, the resistance in 30°C-acclimated fish is higher.4.Mucosal glucose application evokes a change in the transepithelial potential difference. Although this effect is smaller in the intestines of 30°C-acclimated fish, a sustained change in potential difference due to the presence of glucose is observed in both cases.5.Transepithelial sugar transport across in vitro intestinal preparations was measured using 3-oxy-methyl-d-glucose as a substrate. At 30°C the net flux, expressed in mmol·kg wet weight−1·h−1, is larger in intestinal mucosa of 30°C-acclimated fish than in mucosa of 10°C-fish.6.Ion content was determined in both freshly isolated muscosa and mucosa incubated for 1 h at 20°C. The sodium concentration in intestinal cells from 30°C-acclimated fish was found to be higher.7.Oxygen consumption by intestinal mucosa was determined at 20°C in the absence and presence of ouabain. The difference in ouabain-sensitive oxygen consumption between 10°C-fish or 30°C-fish is not significant.

Sodium-dependent sugar and amino acid transport in isolated goldfish intestinal epithelium: electrophysiological evidence against direct interactions at the carrier level.

AbstractThe effects of mucosal application of monosaccharides and amino acids on transepithelial and membrane potentials in isolated goldfish intestinal epithelium were investigated.Isosmotic replacement of mucosal mannitol by sugars orl-amino acids resulted in a rapid depolarization of the mucosal membrane potential ψmc followed by a slow repolarization. Phlorizin inhibited the responses to sugar but not those to amino acids. d-Amino acids did not induce any electrical response in the epithelium. Dose-response curves forl-amino acids showed simple saturation.Simultaneous application ofl-amino acid and glucose induced transepithelial responses of about 80% of the sum of the separate responses to the application of amino acid or glucose alone. Simultaneous application of different amino acids in saturating concentrations did not increase the magnitude of the electrical responses.From the measured changes in potentials we calculated the change in electromotive force across the mucosal (ΔEm) and serosal (ΔEs) membrane. The change inEm induced by combined application of alanine and glucose was 90% of the sum of the calculated values induced by glucose and alanine alone. The response ofEs to both substrates was accelerated with respect to that of separate substrates alone.We conclude that by application of glucose in addition to alanine the influx of sodium is increased, thereby stimulating the basolaterally located electrogenic Na+/K+-pump. There are no indications for direct interaction of sugars and amino acids at the mucosal membrane of the intestinal epithelial cell.

Microscopical determination of the filtration permeability of the mucosal surface of the goldfish intestinal epithelium

SummaryThe rate of shrinkage of the mucosal folds of goldfish intestine in response to mucosal hypertonicity was measured by microscopic means. Because of the geometry of the intestinal folds the rate of shrinkage could be directly related to the loss of volume from the fold through the brush border membranes and tight junctions. Experimentally a wide range of velocities was observed, reflecting the difficulty of rapidly estabilishing a uniform osmotic gradient at the preparations mucosal surface. The initial velocity of volume loss provided a measure of the filtration permeability (Pf) of the mucosal surface. From the highest velocities observed the filtration permeability was estimated to be approximately 14×10−3 cm/sec related to the folded mucosal surface and 65×10−3 cm/sec related to the straight serosal surface. Consideration of the experimental errors and unstirred layer effects make it probable that the latter value is still an underestimate of the truePf. The series barriers of the epithelium cause the total tissuePf to be less than thePf of the mucosal surface alone. In addition thePf measured in the presence of an osmotic gradient may differ substantially from the tissue filtration permeability which exists in the absence of a change in osmolarity.

Electrical Phenomena in Fish Intestine

This article is an attempt to review electrical phenomena in fish intestinal preparations. In the first two sections the various preparations and their electrical characteristics will be described. In the next section, the equivalent electrical circuit and a geometrical representation of the equations used as a solution of the equivalent circuit as introduced by Bakker (1980) will be presented. Then the electrical characteristics will be discussed on the basis of the equivalent circuit and the question of an active CI- transport in seawater fish will be debated. The final section will deal with sugar-and amino acid-evoked potentials.

Analysis of the ouabain-induced increase in transepithelial electrical resistance in the goldfish intestinal mucosa

Abstract1.The ouabain-induced increase in transmural resistance of goldfish intestinal mucosa stripped free from underlying muscular layers is analysed by comparing the resistance increase in normal and in low chloride saline, the resistance increase induced by anaerobic conditions and the resistance increase provoked by hypotonicity.2.It is concluded that the collapse of the lateral intercellular space is the prime reason for the resistance increase and that the lateral intercellular space is maintained dilated by a ouabain-sensitive solute transport mechanism.3.This mechanism can be either a rheogenic or a neutral Na/K-pump. In the latter case additional conditions have to be specified concerning values for ion concentrations in the lateral intercellular space and in the unstirred layer adjacent to the luminal membrane.4.There are no indications for a chloride dependent mechanism involved in the maintenance of the width of the lateral intercellular spaces in the goldfish intestinal mucosa.

Effects of serosally added sugars on the transepithelial electrical properties of the perfused goldfish intestine

Summary1.A study has been made of the effect of serosally added sugars on the transmural potential difference and electrical resistance of the perfused goldfish intestine.2.Addition of glucose at the serosal side resulted in a decrease of the transmural potential difference independent of the presence or absence of glucose at the mucosal side. The transepithelial resistance did not change.3.The serosal glucose effect persisted in the presence of phlorizin at the mucosal side.4.With the actively transported non-metabolized glucose analogue 3-oxy-methyglucose the same effects were observed as with glucose.5.Replacement of NaCl by cholineCl, RbCl or LiCl at both sides of the intestine had a diminishing effect on the glucose evoked potentials and on the transepithelial conductance.6.Phlorizin in concentrations lower than 10−4 M, at the serosal side did not influence neither the mucosal nor the serosal glucose effects.7.Ouabain at the serosal side inhibited the serosal glucose effect and decreased the transepithelial conductance.8.The results support the concept that sugar transport at the serosal side of the epithelial cell has features in common with the sodium-dependent sugar transport mechanism at the mucosal side.