Effect of Sugars on Transport of Alanine in Intestine

Abstract

The eflect of glucose and galactose on transport of alanine by rabbit ileum has been investigated. Transmural transport and cellular ac cumulation of the amino acid were in hibited by the sugars, but alanine in flux across the mucosal border of the cells was unaltered.

Transport of neutral and cationic amino acids across the brush-border membrane of the rabbit ileum

“…In contrast, indicating a faster basolateral response to the increased flux of sodium across the brush-border membrane (Schultz,198l), only very moderate degrees of depolarizations have been observed in mammalian small intestines (Rose & Schultz, 1971). In agreement with these observations, in the rabbit ileum Jm Ala was not significantly inhibited by glucose or galactose (Chez, Schultz & Curran, 1966) and in the rat and guinea pig the mutual inhibition between sugars and a.a. amounted to only 10 to 15% (Munck, 1972(Munck, , 1980Robinson & Alvarado, 1977). The 14% inhibition which lysine caused to the transport of 1 mM galactose in the presence of 90 mM alanine is consistent with these results.…”

Interaction between Na+-dependent transport systems for sugars and amino acids. Evidence against a role for the sodium gradient

“…Higher 3-OMG concentrations produce correspondingly greater inhibitory effects until at 10 mM 3-OMG about 60 % of the active valine transport is prevented. By contrast, sugar concentrations between 20 and 28 mM are typically required to achieve [10,30]. Active transport is defined as that part of the total valine entry which is DNP sensitive.…”

Counter‐transport between sugars and amino acids in rabbit ileum

“…These workers failed to demonstrate an inhibition of unidirectional influx of an amino acid (L-alanine) into mucosal cells of rabbit ileum from which result they deduced without direct evidence that the interaction of sugars and amino acids takes place at the inner face of the membrane, galactose stimulating amino acid efflux. We are quite unable to explain the lack of agreement between the two laboratories, using the same animal, but it may be pointed out that the work of Chez et al [5] was carried out with a somewhat different technique and was limited to inhibition studies: no attempt was made to study counter-transport, nor to measure efflux directly (as has in fact been done in other heterologousinteraction studies [ 16 ]). In order to ascertain whether the discrepancies could possibly be due to the use of different substrates, we performed a series of countertransport experiments analogous to those shown in the figure, but using alanine as substrate.…”

“…The fourth suggestion is that an allosteric inhibition between the two groups of compounds occurs at the outer face of the membrane, this being caused by the contiguity of two binding sites in the membrane surface [7]. The apparent irreconcilability of the last two possibilities led Alvarado [8] to propose that dissimilar mechanisms may operate in different species, since strong evidence existed in favour of the fourth hypothesis in the case of the hamster intestine, whereas results from other laboratories appeared to place doubt on its applicability to the rabbit [5] and dogfish [6]. The unsatisfactory nature of this conclusion, however, provoked us to study the interactions between sugars and amino acids in one of the controversial species, the rabbit, by means of a method which theoretically should distinguish between events occurring at the level of the mucosal rather than other membranes of the intestine.…”

“…The arguments against these two hypotheses are weighty and have been discussed in detail elsewhere [4] ; they need not be repeated here. A third proposal is that the primary interaction occurs at the inner face of the membrane, apparent inhibition of uptake occurring by acceleration of efflux [5,6]. The fourth suggestion is that an allosteric inhibition between the two groups of compounds occurs at the outer face of the membrane, this being caused by the contiguity of two binding sites in the membrane surface [7].…”