Chloride-dependence of amino acid transport in rabbit ileum

Chloride-dependence of influx across the brush-border membrane of distal rabbit ileum was examined for beta-alanine, 2-methylaminoisobutyric acid (MeAIB), leucine, lysine, proline and D-glucose. Influx of leucine at 2 mM and of D-glucose at 0.5 mM was chloride-independent indicating that substitution of isethionate for chloride has no unspecific effect on sodium gradient driven transport processes. In contrast influx of beta-alanine and MeAIB was totally dependent on the presence of chloride ions. In the absence of chloride, proline transport was reduced to 20% of its control level. This remaining transport can be accounted for by the function of the carrier of alpha-amino-monocarboxylic acids. Transport of leucine at 0.1 mM was reduced by absence of chloride. This is in accordance with the observation of leucine transport by the beta-alanine carrier. The kinetics of chloride and sodium activation of transport of MeAIB were examined at 1 mM MeAIB. Chloride activation was characterized by a Hill coefficient of 1 and a K1/2 of 23.5 mM, and sodium activation by a Hill coefficient of 2 and a K1/2 of 51 mM. Thus cotransport of chloride with an imino acid would be compatible with the known rheogenic nature of this transport. This study adds the imino acid carrier and the beta-alanine carrier to the group of chloride-dependent, epithelial amino acid transport systems.     

Enkephalin regulation of L-valine transport in rabbit ileum

We studied the influence on ionic basal transport (Na+ and Cl-) and L-valine transport of two enkephalins which are not metabolized and act in delta and mu receptors respectively. Transports have been indirectly determined measuring the transepithelial electric potential and the short circuit current. DADLE does not significantly influence ion and amino-acid transport, while DAGO alters both of them in the presence of the myenteric plexus (muscle layers present) or inhibits only L-valine transport in the absence of the plexus (muscle layers removed).     

Effects of inhibitors on 3-O-methylglycose transport in rabbit ileum

Summary Previous studies (Goldner, Schultz & Curran,J. Gen. Physiol. 1969,53:362) have suggested a direct coupling between influxes of sugars and Na across the brush border membrane of rabbit ileum. Effects of several inhibitors, ouabain, cyanide, dinitrophenol and iodoacetate on 3-O-methylglucose fluxes were examined in an effort to obtain information about coupling of sugar transport to metabolism. The inhibitors virtually abolished net active sugar transport across the whole tissue but had less striking effects on sugar influx across the brush border membrane, particularly when the cells were prevented from gaining Na as a result of inhibitor action. However, substantial but incomplete inhibition of influx was observed when the cells were permitted to gain Na. Mucosal strips incubated with ouabain to elevate cellular Na extruded sugar against a concentration gradient when cell Na concentration exceeded that in the medium. Conversely, a small extrusion of Na from ouabain-poisoned cells was observed in the presence of an outwardly directed concentration gradient for sugar. These results provide further evidence of coupling between Na and sugar movement. Additional direct coupling of sugar movement to metabolism cannot be ruled out.     

Effect of papain treatment on phenylalanine transport in rabbit ileum.

The unidirectional influx of phenylalanine across the mucosal brush border of rabbit ileum is reduced by pretreatment with papain. Phenylalanine influx is reduced to 10–15% of the control value by 60–90 minutes of preincubation with papain. Pretreatment with protease from $\text{Streptomyces griseus}$ has no effect on phenylalanine influx. Kinetic analysis of the effect of papain indicates that the maximum velocity is reduced with little change in the apparent Michaelis-constant for phenylalanine. The data suggest that papain attacks a membrane protein required for transport. This protein is unaffected by protease which indicates the susceptible region of the protein is shielded by the membrane or inaccessible to protease.     

Effect of phenethylbiguanide on sugar and amino acid transport in rabbit ileum

Phenethylbiguanide has been shown to be an inhibitor of sugar and amino acid uptake in both $\text{in vivo}$ and $\text{in vitro}$ conditions. This action could be due to a competition for sodium sites on the sugar and amino acid carrier molecules. The effects of phenethylbiguanide on $\text{in vitro}$ intestinal preparations indicate that this compound has a time-dependent effect, it is most effective when placed on the mucosal surface but is also effective on the serosal surface. Furthermore, competition studies indicate that it is a competitive inhibitor of sugar uptake and a non-competitive inhibitor of amino acid uptake. These results are consistent with the differences in the mechanism of coupled transport between sugars and amino acids, but, do not substantiate the idea that phenethylbiguanide competes for the sodium site on the ternary carrier.     

Effect of cholera toxin on glutamine metabolism and transport in rabbit ileum

The aim of the present study was to evaluate the effect of cholera toxin on energy balance from intestinal glutamine metabolism and oxidation, glutamine-dependent sodium absorption, and cholera toxin-dependent ion flux. Cholera toxin-stimulated sodium and L-glutamine ileal transport and metabolism were studied in Ussing chambers. Glutamine (10 mM) transport and metabolism were simultaneously studied using (14)C flux and HPLC. In the same tissues, the flux of each amino acid was studied by HPLC, and glutamine metabolism and oxidation were studied by the determination of amino acid specific activity and (14)CO(2) production. In control tissues, glutamine stimulated sodium absorption and was mainly oxidized. The transepithelial flux of intact glutamine represented 45% of glutamine flux across the luminal membrane. The other metabolites were glutamate and, to a lesser degree, citrulline, ornithine, and proline. Cholera toxin did not alter glutamine-stimulated sodium absorption, glutamine oxidation, transport, and metabolism. In conclusion, the present results indicate that cholera toxin does not alter glutamine intestinal function and metabolism. In addition, approximately 95% of the energy provided by glutamine oxidation remains available to the enterocyte.     

Na and Cl transport and short-circuit current in rabbit ileum

Summary Na and Cl fluxes and short-circuit current (I _sc) in rabbit ileum have been studied as a function of ionic concentrations in HCO₃-free solutions. Both net Na flux (J _net ^Na ) andI _sc show similar saturation functions of [Na] at fixed [Cl]. They show no significant difference between zero and 112mm Na but at 140mm NaI _sc is significantly greater than theJ _net ^Na . Net Cl transport, secretion, is observed only at 140mm Na and is approximately equivalent to the difference between theI _sc andJ _net ^Na . The transcellular mucosa-to-serosa Na fluxes measured at 140 and 70mm Na do not differ significantly from the correspondingI _sc. The net Cl flux varies with [Cl] at fixed [Na] whileI _sc is virtually not affected by [Cl]. These results suggest that the absorptive Na transport process is electrogenic and responsible for theI _sc and that the secretory fluxes of Na and Cl are coupled, require high [Na], vary with [Cl], and do not contribute toI _sc. K-free solution abolishes theI _sc after a prolonged lag. Finally, the effect of a low resistance shunt pathway on active Na absorption is examined with a four-compartment model.Deceased (October 16, 1974).     

Effects of galanin on short circuit current and electrolyte transport in rabbit ileum

Galanin decreased short circuit current (I_sc) and increased

Abstract

Galanin decreased short circuit current (I_sc) and increased active Na⁺ and Cl⁻ absorption in rabbit ileum. In the absence of calcium, the galanin-induced decrease in I_sc was inhibited by approximately 60%. Tetrodotoxin significantly reduced the effect of galanin on I_sc, and tetrodotoxin and EGTA totally blocked the effect, indicating that the nonneuronal mediator of the effect is Ca²⁺ dependent. Galanin binding to basolateral membranes prepared from ileal epithelial cells was specific and of high affinity. These results suggest the involvement of this peptide in the regulation of intestinal epithelial cell function.     

Salmon calcitonin and water and electrolyte transport in rabbit ileum.

The administration of SCT, natural and synthetic, has no apparent effect on the ileal water and electrolyte transport in the rabbit. The failure of SCT to influence ileal transport of water and electrolytes in the rabbit, as it does in man, may be due to differences in the rabbit intestinal response to a foreign peptide hormone.     

Effect of aldosterone on ion transport by rabbit colonIn vitro

Summary Segments of descending colon obtained from rabbits, that had been maintained on drinking water containing 25mm NaCl and an artificial diet which contains 1% Na and is nominally K-free, respond to aldosterone in vitro (after a 30 to 60-min lag period) with a marked increase in the short-circuit current (I _sc ), an equivalent increase in the rate of active Na absorption (J _net ^Na ) and a decline in tissue resistance (R _t ). Aldosterone also brings about a marked increase in the unidirectional influx of Na into the cells across the mucosal membrane (zero-time rate of uptake) which does not differ significantly from the increase inI _sc . Treatment of control tissues with amphotericin B brings about sustained increases inI _sc andJ _net ^Na to levels observed in aldosterone-treated tissues. However, addition of amphotericin B to the mucosal solution of aldosteronetreated tissues does not result in a sustained increase inI _sc orJ _net ^Na and these values do not differ markedly from those observed in control tissues treated with amphotericin B. These findings, together with other evidence that Na entry in the presence of amphotericin B is sufficiently rapid to saturate the active Na extrusion mechanism at the baso-lateral membrane, are consistent with the notion that the aldosterone-induced protein increases the permeability of the mucosal membrane to Na but does not increase the saturation level of the active Na pump within the time-frame of these studies (3 hr).Finally, aldosterone has no effect on the bidirectional or net transepithelial movements of K under short-circuit conditions, suggesting that the enhanced secretion of K observed in vivo is the result of increased diffusion of K from plasma to lumen via paracellular pathways in response to an increased transepithelial electrical potential difference (lumen negative).     

Influence of electrical gradient on electrolyte and water transport in rabbit ileum and colon in vitro

We studied the influence of the electrical gradient between the mucous and serous side on water and electrolyte transport in the rabbit distal ileum and proximal colon "in vitro". In the absence of a gradient, the absorption of water, sodium, chloride and bicarbonate rose in both ileum and colon, whereas potassium secretion tended to give way to potassium absorption.