AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 4 306-G310, Copyright © 1980 by American Physiological Society
Tryptophan transport by isolated newborn rabbit jejunum
H. J. Cooke, L. Pfankuche and A. R. Cooke
Segments of newborn or adult rabbit jejunum were mounted as flat sheets in
flux chambers. Mucosal-to-serosal (Jm leads to s) and serosal-to-mucosal
(Js leads to m) fluxes of tryptophan (Try), phenylalanine (Phe), and
alanine (Ala) were measured in the absence of electrochemical gradients. In
the presence of Na, J Try s leads to m increased linearly with
concentration, whereas the relationship of J Try m leads to s and
concentration contained both linear and saturating components. The
relationship of net Try flux and concentration was in accord with
Michaelis-Menten kinetics. Ouabain (10(-3) M) abolished net Na fluxes in
both newborn and adult rabbit jejunum and abolished net Try flux in the
adult, but did not reduce net Try flux to zero in the newborn. In the
presence of Na-free solutions small net fluxes of Try, Phe, and Ala
occurred in the newborn. Addition of 10(-4) M 2,4-dinitrophenol abolished
net Try flux in ouabain-treated newborn rabbit jejunum that was bathed by
either Na-free or Na-containing solutions. In the presence of Na, Phe and
Ala reduced J Try m leads to s, and Try reduced the fluxes of Phe and Ala.
Phe inhibited J Try m leads to s in Na-free solutions, and Try reduced J
Phe m leads to s. These results suggest that the newborn rabbit jejunum
resembles the adult in that Try is absorbed primarily by a Na-dependent
system. These results show that the newborn differs from the adult in that
Try is absorbed by a system that is independent of Na but requires
metabolic energy.
