AJP - Gastrointestinal and Liver Physiology, Vol 242, Issue 4 308-G312, Copyright © 1982 by American Physiological Society
Effect of tryptophan on transport properties of newborn rabbit jejunum
H. J. Cooke and A. R. Cooke
The effect of tryptophan on sodium and chloride fluxes was determined
simultaneously on paired flat-sheet preparations of newborn rabbit jejunum
under short-circuit conditions. In the absence of amino acids, the newborn
rabbit jejunum actively absorbed sodium, and possibly bicarbonate, whereas
chloride appeared to be distributed passively across the jejunum.
Tryptophan (2 mM) caused an increment in short-circuit current (Isc) that
was due to an increase in net active sodium flux and had no significant
effect on tissue conductance. At a 10 mM concentration, tryptophan
initially increased Isc, although not to as large a degree as phenylalanine
or alanine, and then caused a progressive decline that reached a plateau
around 60 min. The reduction in Isc was attributed primarily to abolition
of sodium absorption and stimulation of chloride secretion. Tryptophan
reduced the unidirectional fluxes of sodium, increased those of chloride,
and decreased total tissue conductance. These results suggest that 10 mM
tryptophan initially causes a predicted increase in sodium absorption,
followed by an inhibition of sodium absorption and stimulation of chloride
secretion. The mechanism of action of tryptophan resulting in changes in
ion fluxes is unknown.
