AJP - Cell Physiology, Vol 237, Issue 1 56-C63, Copyright © 1979 by American Physiological Society
Energetics of sugar transport by isolated intestinal epithelial cells: effects of cytochalasin B
G. A. Kimmich and J. Randles
The capability of isolated intestinal epithelial cells to establish
concentration gradients of 3-O-methylglucose (3-OMG) by a Na+-dependent
transport system is limited by concomitant function of a Na+-independent,
facilitated diffusion transport system. Monosaccharides accumulated by the
active system are continuously lost via the passive system, which acts to
lower steady-state sugar gradients maintained by the cell. Cytochalasin B
is a potent inhibitor of the passive system and allows the cells to
establish a sugar gradient that is much higher than normal. When
extracellular [3-OMG] is 1 mM, cytochalasin induces sugar accumulation
ratios of 30-fold (+/- phlorizin) in contrast to control ratios of
approximately 10-fold. When [3-OMG] is 0.1 mM, cytochalasin (0.1 mM)
induces 40-fold accumulation ratios. When changes in extracellular sugar
concentration are considered, steady-state concentration gradients observed
are 70-fold. For a Na:sugar coupling stoichiometry of 1:1, gradients of
this magnitude represent the approximate theoretical maximum for a
transport system driven exclusively by the transmembrane electrochemical
potential for Na+.
