Joseph Lerner

Intestinal absorption of choline in the chick.

Abstract The intestinal absorption of choline in the chick has been studied in 1-min incubations using a tissue-accumulation method. There are two processes involved in choline absorption, mediated route with an apparent Km of 100 μM and a maximum velocity V of 25 nmoles/ml tissue water per min and a diffusion mechanism. Lowering the external Na+ concentration leads to an increase in apparent Km but to no change in V. Mediated choline entry is not sensitive to anaerobiosis, ouabain or oligomycin. The transport of choline can be competitively inhibited by structural analogs, the best inhibitors being hemicholinium-3 and N,N-dimethylethanolamin which also cause trans-inhibition. Choline influx, however, is independent of intracellular choline. Although the transports of choline and thiamine are mutually antagonistic, results of a kinetic test indicate that there probably is not a single common site for choline and thiamine absorption.

KINETICS OF METHIONINE INFLUX INTO VARIOUS REGIONS OF CHICKEN INTESTINE

Abstract o 1. The intestinal absorption of methionine has been studied by an in vitro tissue-accumulation technique in the chicken. 2. Carrier-mediated transport for this amino acid was found in the duodenum, jejunum, ileum and colon in week-old chicks the affinity and capacity of the small intestine for methionine absorption are relatively constant from proximal duodenum through the ileum. 3. The colon in hens can absorb methionine by a saturable process, suggesting that the large intestine functions in the adult. 4. The caecum in day-old chicks transports methionine by way of two kinetically distinct processes, one with high affinity and low capacity, and another with low affinity and high capacity. 5. By the end of the first week of life, the caecum no longer possesses the ability to transport methionine or alanine by a carrier mechanism. 6. A comparison of specificity limits of methionine uptake at low substrate concentration in the colon and caecum revealed a contrasting order of maximal inhibitions brought about by a series of amino acids. This information, along with the kinetic findings, suggests the presence of different mechanisms for methionine absorption in the caecum and colon.

Cationic amino acid transport in chicken small intestine.

Abstract 1. 1. The cationic amino acids have been shown to represent a transport class in the chicken small intestine on the basis of their competition for what appears to be a single transport site. 2. 2. This site does not appear to be the primary site of histidine entry. 3. 3. Leucine is a strong competitive inhibitor of arginine uptake, while the influence of arginine upon the influx of leucine is slight. 4. 4. Comparison of inhibition of lysine and methionine by various amino acids and analogs showed that the inhibition of lysine by neutral amino acids occurs by their attachment to a site other than the one involved in the uptake of methionine.

Distinct components of neutral amino acid transport in chick small intestine

Abstract 1. 1. The intestinal absorption of alanine, β-alanine, α-aminoisobutyric acid (AIB), glycine, proline and tryptophan has been studied by an in vitro tissue accumulation method in the chick. 2. 2. The use of amino acids as specific blocking agents allowed for the characterization of seven discrete components of neutral amino acid transport which can be grouped into three major categories: (a) those processes inhibited by leucine and glycine; (b) those inhibited by leucine, but not by glycine; (c) those not inhibited by leucine.

Cell membrane amino acid transport processes in the domestic fowl (Gallus domesticus)

Intestinal absorption of amino acids in the chicken occurs by way of processes which are concentrative, Na+-dependent and dependent upon metabolic energy in the form of ATP. Intestinal transport is carrier-mediated, subject to exchange transport (trans-membrane effects) and is inhibitable by sugars, reagents which inactivate sulfhydryl groups, potassium ion, and by deoxpyridoxine, an anti-vitamin B6 agent. It is stimulated by phlorizin, a potent inhibitor of sugar transport, and in Na+-leached tissue by modifiers of tissue cyclic AMP levels, e.g. theophylline, histamine, carbachol and secretin. Separate transport sites with broad, overlapping specificities function in the intestinal absorption of the various classes of common amino acids. A simple model for these sites includes one for leucine and other neutral amino acids, one for proline, beta-alanine and related imino and amino acids, one for basic amino acids, and one for acidic amino acids. Absorption of amino acids appears to be widespread in occurrence in the digestive tract of the domestic fowl; transport has been reported to be present in the crop, gizzard, proventriculus, small intestine and in the colon. By the end of the first week of life post-hatch, the caecum loses its ability to transport. Similarly, the yolk sac loses its ability by the second day post-hatch. Intestinal transport was noted before hatch and was found to be maximal immediately post-hatch. A requirement for Ca2+ appears to be lost after the first week of life post-hatch. The cationic amino acids appear to be reabsorbed by a common mechanism in the kidney. Transport rates of leucine measured in the intestine or in the erythrocyte were found to cluster about discrete values when many individual chickens were surveyed; such patterns may be an expression of gene differences between individuals. Two lines of chickens have been developed, one high and the other low uptake, through selective breeding based on the ability of individual birds to absorb leucine in erythrocytes. High leucine absorbing chickens were found to be more effective in absorbing lysine and glycine, were more effectively stimulated by Na+, had greater erythrocyte Na+, K+-ATPase activity, and their erythrocytes contained about 20% less Na+ than low line erythrocytes. The underlying genetic difference between these lines may reside at the level of the Na+, K+-ATPase and (or) with a regulatory gene determining carrier copies. Amino acid transport in erythrocytes was noted to be highest in pre-hatch chicks and to diminish during post-hatch development.(ABSTRACT TRUNCATED AT 400 WORDS)

A distinct, Na+-dependent glycine transport system in avian small intestine

Abstract The intestinal absorption of glycine in the chicken has been studied by a tissue-accumulation procedure. Glycine entry is dependent upon Na + and is inhibited by anaerobiosis. By a kinetic test it has been shown that glycine is absorbed at a site different from the neutral (methionine) transport site previously characterized in this species. The glycine site has highest affinity for glycine, alanine, and other neutral amino acids, in that order. The order of affinities for the methionine site is: nonpolar, neutral amino acids>alanine>glycine. For the glycine site, the affinities of neutral amino acids are about one order of magnitude smaller than for the methionine site. However, like the methionine site preference for l -amino acids is seen, and acidic and basic amino acids have little or no affinity. Additionally, requirements are noted for an α-hydrogen atom and for a free α-amino group; substrates such as α-aminoisobutyric acid, proline, hydroxyproline, sarcosine and β-alanine do not interfere with glycine entry. Glycine, when used as a test inhibitor, has little influence on the absorptions of glutamic acid, lysine, alanine, or proline. The shapes of the time courses of glycine and methionine uptake are similar, and both amino acids have Q 10 values of about 1.7.

Intestinal absorption of glutamic acid in the chicken

Abstract 1. 1. The intestinal absorption of glutamic acid in the chicken has been studied using a tissue-accumulation method. 2. 2. There were two processes involved in glutamic acid absorption, a mediated route with high apparent affinity and a diffusion mechanism. 3. 3. Glutamic acid influx was inhibited by metabolic poisons, lack of Na in the incubation medium and various structural analogs. 4. 4. Glutamic acid had little effect on basic or neutral amino acid transport. 5. 5. The results suggest that a distinct transport system exists for acidic amino acids in the chicken intestine.

Effect of theophylline and Na+ on methionine influx in Na+-depleted intestine.

Abstract The unidirectional influx of methionine into the brush border epithelium of chicken jejunum has been studied. Tissues leached of Na+ transport methionine from a medium devoid of Na+ with reduced apparent affinity (Kt) and maximal flux (Jmax). Addition of Na+ to the medium during a 1-min incubation with substrate, or during a 30-min preincubation, restored Kt but affected Jmax slightly. Theophylline was found to maintain Jmax in the absence of Na+. Essentially complete restoration of Kt and Jmax could be attained when theophylline-treated tissue was exposed to Na+ for 30 min. Influx from a Na+ medium was unaffected by theophylline pretreatment in Na+-containing buffer. Kt was increased without an effet upon Jmax when influx was studied from choline medium following preincubation in Na+. Modifiers of tissue cyclic AMP levels were investigated in conjunction with theophylline. Histamine and carbachol were found to inhibit theophylline-stimulated transport. Secretin was found to stimulate influx in Na+-leached tissue, but did not potentiate the theophylline effect. Amino acids in the incubation medium inhibited theophylline-stimulated influx, whereas preloaded lysine or methionine had no effect. The results are interpreted in terms of a model which envisions roles for cellular and external Na+ and for cyclic AMP in the activation and regulation of amino acid transport in intestine.

A distinct component of proline transport in chicken small intestine.

Abstract 1. 1. The specificity of proline for intestinal absorption in tne chicken is complex in that approximately 40 per cent of the uptake of 0·8 mM proline takes place in a leucine-shared transport system(s), while a smaller component of its uptake occurs in a separate system(s) shared with other secondary amino acids. 2. 2. This latter component, presumably an imino acid carrier system, is devoid of reactivity with glycine and, hence, constitutes a separate agency from the previously described glycine transport system in chicken small intestine.

The effect of preloaded amino acids on lysine and homoarginine transport in chicken small intestine.

Abstract 1. 1. Preloaded neutral and basic amino acids were observed to enhance the 1- and 5-min uptakes of lysine and homoarginine into sections of chicken small intestine incubated in vitro . 2. 2. This so-called transstimulatory phenomenon, in analogy to previous findings reported for rat and rabbit intestine, was shown to be a Na + -indepentent process. 3. 3. The transinhibition of basic amino acid transport affected by preloaded homoarginine or arginine was noted to be a Na + -dependent process. 4. 4. Our results are consistent with the notion that preloaded amino acids may act to accelerate uptake by an exchange diffusion mechanism and (or) by inhibition of substrate loss from the tissue.