AJP - Gastrointestinal and Liver Physiology, Vol 259, Issue 5 775-G780, Copyright © 1990 by American Physiological Society
Glycyl-L-sarcosine transport by ATP-depleted isolated enterocytes from chicks
M. L. Calonge, A. Ilundain and J. Bolufer
Departamento de Fisiologia y Biologia Animal, Facultad de Farmacia, Universidad de Sevilla, Spain.
Normally energized and ATP-depleted isolated chicken enterocytes have been
used to investigate the energetics of intestinal glycyl-L-sarcosine
(Gly-Sar) transport, and the results were compared with those obtained for
3-O-methyl-D-glucose (3-OMG) active transport, which is known to be
energized by the electrochemical Na+ gradient. The results show that even
though Gly-Sar had no effect on Na+ efflux from labeled (22Na) enterocytes,
20 mM L-leucine and 20 mM 3-OMG increased the rate constant of Na+ efflux
by 34 and 76%, respectively. In ATP-depleted cells 3-OMG was accumulated in
response to experimentally imposed inward Na+ gradients; however, Gly-Sar
was not accumulated. In the absence of Na+, an inward proton gradient
slightly increased Gly-Sar uptake, although no transient accumulation was
observed. An increase in membrane potential by replacement of Cl- by NO3-
or by imposition of an outward K+ gradient in the presence of valinomycin
stimulated both 3-OMG and Gly-Sar uptake, even in the absence of either H+
or Na+ gradient. When in addition to a K+ diffusion potential, a Na+
gradient was present, 3-OMG transient accumulation was further increased
(approximately 2-fold over equilibrium value), and Gly-Sar uptake showed
the same pattern as that observed when only membrane potential was present.
However, in the presence of an outward K+ diffusion potential and an inward
H+ gradient Gly-Sar was stimulated approximately threefold, clearly showing
a significant overshoot, whereas 3-OMG was not transiently accumulated.
