Lysine Transport across Isolated Rabbit Ileum

Abstract

Lysine transport by in vitro distal rabbit ileum has been investigated by determining (a) transmural fluxes across short-circuited segments of the tissue; (b) accumulation by mucosal strips; and (c) influx from the mucosal solution across the brush border into the epithelium. Net transmural flux of lysine is considerably smaller than that of alanine. However, lysine influx across the brush border and lysine accumulation by mucosal strips are quantitatively comparable to alanine influx and accumulation. Evidence is presented that the "low transport capacity" of rabbit ileum for lysine is due to: (a) a carriermediated process responsible for efltux of lysine out of the cell across the serosal and/or lateral membranes that is characterized by a low maximal velocity; and (b) a high "backflux" of lysine out of the cell across the mucosal membrane. A possible explanation for the latter observation is discussed with reference to the relatively low Na dependence of lysine transport across the intestinal brush border.The ability of small intestine to transport neutral amino acids from a lower concentration in the mucosal solution to a higher concentration in the serosal solution was first demonstrated by Wiseman in 1951 (1). Since then the transport of neutral amino acids b y in vitro preparations of mammalian small intestine has been the subject of numerous investigations and has been described in considerable detail. In 1961, Hagihira et al. (9) demonstrated transport of the basic amino acids across everted sacs of hamster small intestine against a concentration difference using low initial concentrations in the mucosal and serosal fluids. These investigators noted that the maximal rates of transport of the basic amino acids were only 5 -1 0 % of the rates of transport of neutral amino acids and concluded that the earlier failure to demonstrate net transport in the presence of high initial mucosal and serosal concentrations (3) could be attributed to this small transport "capacity." Since 1961, there have been relatively few studies dealing with the characteristics of basic amino acid transport across in vitro small intestine, but nevertheless the initial observations and conclusions of Hagihira et al. have been substantially confirmed (4-8).This "small transport capacity" of in vitro small intestine for basic amino acids raises several questions.

Distinguishing transport systems having overlapping specificities for neutral and basic amino acids in the rabbit ileum.

“…The dependence of uptake on lysine concentration became more linear over the concentration range 3-60 mM. These results confirm those published previously by Munck & Schultz (1969b), showing lysine entry into rabbit ileum to take place through two transport Lysine uptake by rabbit ileal mucosa measured alone or in the presence of increasing concentrations of alanine. The presentation of results is as described in the legend to Fig.…”

“…There is also a Na-dependent component to lysine uptake (Munck & Schultz, 1969b). The results of preliminary experiments showing the ability ofalanine to inhibit Na-dependent lysine uptake and the ability of lysine to inhibit Na-dependent alanine uptake are summarized in Table 2.…”

“…Such an investigation appeared overdue since the finding that both lysine (Munck & Schultz, 1969b) and neutral amino acids (Sepulveda & Smith, 1978;Paterson, Sepulveda & Smith, 1979, 1980a used two carrier-mediated systems for uptake. Experiments were carried out rapidly after a preliminary incubation in amino acid free medium to minimize any possible complication of the type listed above.…”

Lysine transport across rat jejunum: distribution between the transcellular and the paracellular routes.

“…Nevertheless, together with the data on intracellular accumulation of lysine (Table 4) the concentration dependence of the transcellular fraction of Jl38 (Table 1) suggests that the kinetics of J'Y8 are similar to those deduced for J'y" of the rabbit ileum (Munck & Schultz, 1969).…”

Amino acid efflux from rabbit ileal enterocytes.

“…Use of compartmental analysis led, originally, to the conclusion that efflux was carrier mediated (Munck & Schultz, 1969a;Hajjar, Khuri & Curran, 1972; Danisi, Tai & Curran, 1976). The substrate specificity ofthis process has been assessed further by measuring the ability of different amino acids to affect the transport of each other during efflux (Munck & Schultz, 1969b;Cheeseman, 1981Cheeseman, , 1982 and by measuring amino acid influx into vesicles prepared from basolateral membranes (Mircheff, van Os & Wright, 1980).…”