AJP - Renal Physiology, Vol 244, Issue 3 278-F288, Copyright © 1983 by American Physiological Society
Role of the electrochemical gradient for Na+ in D-glucose transport by mullet kidney
S. H. Lee and J. B. Pritchard
Brush border membrane vesicles were prepared from striped mullet (Mugil
cephalus) kidney. As judged by the marker enzyme activities, these
membranes were enriched 10- to 15-fold compared with the initial
homogenate. Uptake of D-glucose was phlorizin sensitive and Na+ dependent.
L-glucose uptake was unaffected by either phlorizin or Na+. D-Glucose
uptake reflected entry into the osmotically active intravesicular space,
not binding to the membranes. When Na+ was increased from 25 to 100 mM, the
maximum velocity of glucose uptake was increased from 92 to 423 pmol . s-1
. mg protein-1, whereas the apparent Km (1.27 +/- 0.23) was not altered as
Na+ increased. 22Na+ uptake by these membrane vesicles was stimulated by
D-glucose and inhibited by phlorizin. These results indicated that Na+ and
glucose entered the vesicles via a cotransport process. Consistent with
this interpretation, it was possible to show that glucose uptake could be
driven by either the chemical or electrical component of the Na+
electrochemical gradient and that the contributions of these two components
were additive when both were present. Finally, it was shown that the
coupling ratio between Na+ and glucose was approximately 1:1. Accordingly,
these results indicate that reabsorption of D-glucose across the brush
border membranes is coupled to the transmembrane electrochemical gradient
of sodium ions.
