Amino acid transport by the small intestine of the rat. Effects of glucose on transintestinal transport of proline and valine

Transmucosal impedance of small intestine: correlation with transport of sugars and amino acids

Transmucosal impedances of isolated perfused segments of jejunum from mice and hamsters were measured at frequencies from 10-100,000 Hz in the presence and absence of sugars and amino acids. Na-coupled transport of organic substrates caused large decreases of transmucosal impedance, reflecting contraction of cytoskeletal proteins controlling permeability of tight junctions, functional surface of basolateral membranes, and width of extracellular pathways. The observed changes of impedance were closely correlated with molar rates of Na-coupled active transport rather than with molecular species. Thus amino acids and sugars having the same molar rates of active transport also have the same effects on transmucosal impedance. It is proposed that a nonspecific increase of intracellular osmotic pressure during active transport is the first step initiating cytoskeletal contraction. Cell volume regulatory responses, including increased basolateral K+ conductance and Ca2+ influx, may be subsequent steps leading to contraction of perijunctional actomyosin, formation of junctional dilatations, and exposure of lateral membranes. Enhancement of oxygen capacity of perfusion fluids (e.g., with fluorocarbon emulsion) is required to maintain viability of isolated intestinal epithelium; in plain oxygenated Ringer-HCO3 solution, the transmucosal impedance is abnormally low and cytoskeletal contractile responses to Na-coupled transport are attenuated. An electrical circuit analog is presented that simulates almost exactly the observed transmucosal impedances and provides quantitative evaluation of the effects of Na-coupled transport of sugars and amino acids on resistances of tight junctions, capacitance of basolateral membranes, and postjunctional resistances of lateral intercellular spaces and villus cores.

Stimulation of L-tryptophan transport by di- and polysaccharides in the small intestine of chicks

In in vivo and in vitro experiments the effect of various carbohydrates on the absorption of L-tryptophan in the chick small intestine was investigated. On feeding the chicks with semisynthetic diet containing 58.5% of carbohydrates a stimulatory effect of glucose, particularly of starch and saccharose, on the entry of L-tryptophan into the portal vein from the chick gastrointestinal tract has been found. Using an in vitro technique the activating effect of starch and disaccharides (maltose, saccharose) on the intestinal transport of L-tryptophan was detected while monosaccharides (glucose, fructose) at different concentrations had no effect on this process or inhibited it. The possibility that energy of disaccharide hydrolysis is used to stimulate transport process is discussed.

Effect of authentic and natural vitamin C and carotene on amino acid absorption

The effect of vitamin C or carotene either from authentic or natural sources on absorption of lysine, glycine and methionine was evaluated. Results revealed that maximum absorption of these amino acids was reached at different intervals from the orally given dose. Addition of ascorbic acid enhanced amino acid absorption and this effect was maximum in case of methionine. Carotene brought about variable effect to the three amino acids tested. Pepper, parsley, or orange juices did not affect the extent of intestinal lysine absorption. Pepper juice enhanced absorption of methionine in contrast to orange and parsley. Glycine absorption was markedly enhanced by addition of orange juice. Ascorbic acid suppelementation to dietary constituents is recommended for better utilization of proteins.

Effects of sugar and amino acid transport on transepithelial fluxes of sodium and chloride of short circuited rat jejunum

1. Using the Ussing Zerahn (1951) technique the relation between short circuit current (I(sc)) and unidirectional ion fluxes across the short circuited rat jejunum has been examined.2. These parameters of jejunal function have been measured in absence of sugars and amino acids and at 10 mM glucose, 28 mM glucose, 28 mM galactose and 20 mM proline. Sulphate has been used as substituent for chloride on both sides of the gut wall and potassium has been used on the serosal side to substitute for sodium. With regard to the effects of proline on I(sc) and ion fluxes, investigations were made to see whether sulphate and potassium substitutions significantly affected proline transport.3. The purpose of the study was to examine the I(sc) seen in sugars and amino acid free conditions and the Delta I(sc) induced by these substances. Further, it was our purpose to examine the validity of extending to amino acids and sugars in general the suggestion that jejunal transport of these substances stimulates an electroneutral secretion of sodium chloride.4. In the absence of sugars and amino acids at least two-thirds of an I(sc) of 50-70 muA/cm(2) are accounted for by a process of chloride secretion located in the deep parts of the epithelium. The remaining one third or less of the I(sc) can be accounted for in terms of net flux of sodium. The results further indicate that a state of hypoxia in the deep part of the epithelium is the cause of the very low I(sc), p.d. on electrical resistance usually found for sacs of everted rat jejunum.5. The increase in I(sc) induced by proline and glucose is best accounted for by the simultaneously induced increase in mucosa to serosa flux of sodium. There is no compelling evidence that proline should increase I(sc) by a stimulation of chloride secretion.6. Proline, glucose (and galactose) stimulate unidirectional fluxes of sodium and chloride. The effects on serosa to mucosa fluxes equal or exceed those on mucosa to serosa fluxes. The effect of proline on mucosa to serosa flux of thiourea exceeds by far that on serosa to mucosa flux. This and the effects of potassium and sulphate substitution lead to the conclusions in (7) and (8).7. Transport of sugars and amino acids induces or stimulates in rat jejunum in vitro an electroneutral secretion of sodium chloride.8. This effect suffices to explain why, in spite of marked increases in I(sc), increments in net flux of sodium are not induced by transport of proline and glucose. It also explains why the effects of sugar and amino acid transport on water transport in vitro are much less than in vivo.

An in vitro study of the intestinal absorption of pyridinium aldoximes

1. The transfer rates of three pyridinium aldoximes, a non-quaternary pyridine aldoxime and choline across the wall of sacs from the jejunum of rats were measured in vitro.2. The transfer rates observed for any one of the quaternary compounds could be inversely correlated with the transmural potential of the particular sac studied, but there was no correlation with the rates of water or glucose transfer.3. 2-hydroxyiminomethyl-N-methylpyridinium iodide (PAM) had a transfer rate seven times less than that of its non-quaternary analogue, 2-hydroxyiminomethyl pyridine.4. Neither neostigmine nor EDTA affected the transfer rate of PAM in the conditions used.5. It was concluded that the transfer of the quaternary compounds could be explained by diffusion through aqueous pores.