Action of mercury on sugar transport across rat small intestine, in vivo

Absorption of galactose from in vivo perfused rat jejunum was inhibited by 0.1-0.5 mM Hg2+. A few minutes' delay was required for maximal inhibition values. The effects remained after saline solution washing but were in part reversed by EDTA and in higher proportion by dithioerythritol. Absorption inhibition could be ascribed to impairment of the sugar-Na phlorizin-sensitive cotransport component: The passive apparently diffusional component that remains under 0.5 mM phlorizin and absorption of L-sorbose were unaffected by the metal. Hg action is explained as due to its binding to thiol and perhaps other chemical groups of proteins, at different depths in the membrane, which are directly or indirectly related to the sugar transport system.     

Isoosmotic transport of fluid across the hamster small intestine in the presence of phlorizin-induced inhibition of sugar transport.

Experiments were performed to investigate whether the fluid transported across the small intestine is isoosmotic with the mucosal solution when the active transport of glucose is partially inhibited. Everted hamster mid small intestine was incubated in one of the following four mucosal solutions: (1) Isotonic control, Krebs-Ringer bicarbonate solution containing 10 mM glucose (KRBSG), (2) Isotonic with phlorizin, KRBSG + 5X10-5 M phlorizin, (3) Hypertonic control, KRBSG + 50 mM mannitol, (4) Hypertonic with phlorizin, KRBSG + 50 MM mannitol + 5x10-5 M phlorizin. The serosal surface of the intestine was not bathed. Results indicate that the transported fluid was always isoosmotic with any of the mucosal solutions used. When the mucosal solution was made hypertonic with mannitol, the concentration of glucose and electrolytes in the absorbate increased, and as a result, the absorbate became hypertonic and isoosmotic with the mucosal solution. The presence of phlorizin either in the isotonic or in the hypertonic mucosal solution decreased the glucose concentration of the absorbate, but the transported fluid became isoosmotic with the mucosal solution due to a higher concentration of Na, K, and their associated anions. Phlorizin caused a decrease in the transmural potential difference. In spite of this, the presence of this glucoside in the mucosal solution increased the transport of sodium in relation to glucose transport. It is suggested that, at the concentrations used, phlorizin inhibits sodium movement through the electrogenic pathway, but increases the transport of this ion through the non-electrogenic route. This increase in neutral sodium transport seems to compensate for the low concentration of glucose in the absorbate, so that the absorbate becomes isoosmotic with the mucosal solution whether the latter is isotonic or hypertonic. It is suggested further that isoosmotic transport of fluid is an inherent property of the small intestine and that there may be an osmoregulatory mechanism in the gut which controls this process.     

Kinetics of the mediated transport and the passive net flux of phenylalanine across the rat small intestine in vivo

The kinetics of L-phenylalanine absorption by rat jejunum, in vivo, has been studied with luminal perfusion (0.68 ml/min) during successive periods at different substrate concentrations. The non-saturable passive component, measured by inhibiting the active transport with 60 mM methionine, was a linear function of the substrate concentration with an apparent mass-transfer coefficient of 1.42 nmoles/cm/min/mmoles/l. The transport component, estimated from the difference between total absorption and the passive component, displays saturation kinetics with an apparent transport constant (Km) of 7.5 mM and maximal transport rate (Vmax) of 107 nmoles/cm/min. Active transport seems to be the main component in absorbing phenylalanine proceeding from the digestion of food proteins.     

Taurine transport across the small intestine of adult and suckling rats

1. Taurine accumulation in intestinal cells of adult and suckling rats reached steady-state after 60 min with an In/Out ratio of 1.46 and 4.66 in the adult and suckling rats respectively. 2. The accumulative capacity of the intestinal strips isolated from suckling rats is almost four times higher than that of adult rats. 3. The steady-state uptake of taurine by the adult and suckling rats intestinal cells is saturable, sodium-dependent and inhibited by ouabain. 4. The calculated Vmax of the mediated component of the steady-state uptake in the suckling rats is three times greater than that of the adult rats, and the affinity is seven fold greater in the suckling as compared to the adult. 5. Taurine influx across the mucosal membrane in the suckling rat is significantly greater than that of the control adult.     

Effect of enzymatic digestion on phenylalanine transport across the small intestine

Phenylalanine accumulation in mucosal strips isolated from rat small intestine was significantly inhibited (P less than 0.01) after preincubation with trypsin, chymotrypsin, phospholipase D and neuraminidase. Unidirectional phenylalanine influx across the small intestine was significantly reduced (P less than 0.01) when the mucosal strips were preincubated with the above mentioned enzymes. Intestinal cell water and volume were not significantly changed (P greater than 0.6) when the intestinal tissues were preincubated with these enzymes.     

Effect of somatostatin on D-galactose transport across the small intestine of rats

Somatostatin was found to diminish control and theophylline-treated tissue sugar accumulation as well as control and also to diminish theophylline mucosal to serosal D-galactose fluxes. When Na+ was removed from the bath solution, sugar transport was unaltered by the presence of somatostatin. The same results were obtained with phlorizin in the medium. These results seem to suggest that the action of somatostatin is restricted to the Na+-dependent sugar carrier located on the brush border of the intestinal epithelium.     

Cytoskeletal control of alanine transport across the rat and turtle small intestine

Procaine inhibited significantly (P less than 0.01) alanine accumulation in the rat intestinal strips in a concentration-dependent pattern, whereas it showed no effect on alanine uptake by the turtle intestinal cells. Colchicine and Vinca alkaloids at 5 X 10(-4) and 1.5 X 10(-6) M respectively caused a significant inhibition (P less than 0.01) of intracellular alanine concentration in the rat with no effect noticed in the turtle. Unidirectional influx of alanine across the brush border membrane of the rat was significantly (P less than 0.01) reduced in the presence of procaine, colchicine and vincristine in the preincubation medium. The same drugs did not show any effect on alanine influx into the turtle small intestine. Electron microscopy showed major structural alterations in the cytoskeletal organization of the turtle intestine in response to procaine, colchicine or vincristine treatment. It is proposed that microtubular system may participate in the overall transport mechanism of alanine across the small intestine.     

Inhibition of sugar active transport across rat intestine in vivo by cadmium

Galactose absorption by rat jejunum perfused in vivo is inhibited by 0.5 mM Cd2+. This effect is explained by impairment of the phlorizin-sensitive sugar transport system, as Cd does not modify the absorption of L-sorbose or that of galactose in the presence of 0.5 mM phlorizin. Cd inhibition is observed as early as in the 1st minute, does not increase by previous exposure of the mucosa to the metal and does not decrease after washing with saline solution, but it is entirely reversed by EDTA or dithioerythritol. Results agree with a Cd2+ binding to HS- groups of membrane proteins at the brush border, appertaining or functionally related to the phlorizin-sensitive and Na+ dependent transport system for sugars.     

Transamination and asymmetry in glutamate transport across the basolateral membrane of frog small intestine

Transport of L-glutamate across the basolateral membrane of frog small-intestinal epithelium, unlike that of L-alanine, is highly asymmetric; thus the rate constant (K entry) describing the entry of glutamate into the epithelium from the vascular bed across this membrane is one order of magnitude greater than the rate constant (K exit) describing its exit. This asymmetry, which appears not to depend upon the Na gradient, may be important in maintaining a high intracellular concentration of glutamate relative to alanine thereby favouring the production of alanine from glutamate by transamination.     

The components of taurine transport across the rat small intestine A kinetic study

Summary The transport of taurine across adult Sprague-Dawley rat small intestine was studied in vitro using small intestinal strips. The kinetics of the transport mechanism were investigated under both steady-state and influx conditions. Our findings were compatible with the presence of two distinct transport mechanisms; a linear non-carrier mediated component and a saturable carrier mediated component, with almost equal contribution from each. The mediated component was found to be largely Na⁺-dependent and exhibited marked inhibition by B-alanine and structurally related sulfur amino acids.     

Lysine transport in the guinea-pig small intestine

Interactions between cationic and neutral amino acids in transport across the brush-border membrane, Jmc, of the small intestine have been examined using preparations from the distal rabbit ileum and the rat and guinea-pig mid-small intestine. (1) In the guinea pig, the dependence of Jmc Lys on the concentration of lysine is best described in terms of two saturable transport mechanism in addition to free diffusion. (2) It is shown that the discrepancy between cis-effects of low concentrations of neutral amino acids on the Jmc of cationic amino acids, cis-stimulation in the guinea pig contra cis-inhibition in the rabbit and rat, represents species differences. In the guinea pig, imposing sodium-free conditions turns cis-stimulation into cis-inhibition. (3) It is demonstrated that in rat and guinea pig, leucine is transported both by the transport system(s) for cationic amino acids and by transport system(s) which cannot be inhibited by cationic amino acids.     

The effect of local anesthetics on calcium transport across the rat and turtle small intestine

Procaine at different concentrations enhanced significantly (P less than 0.01) calcium accumulation in rat intestinal cells, whereas the same concentrations of procaine inhibited significantly (P less than 0.01) calcium uptake by the turtle small intestine. Unidirectional calcium influx across the rat small intestine was significantly enhanced (P less than 0.001) by the presence of procaine in the preincubation medium. However, procaine had no effect on calcium influx across the turtle intestinal cells. The cell water content and the cell volume were not altered by preincubating the intestinal tissues with procaine in both animals.