AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 3 382-G390, Copyright © 1986 by American Physiological Society
Sodium-proton exchange in colon brush-border membranes
H. J. Binder, G. Stange, H. Murer, B. Stieger and H. P. Hauri
Apical membrane vesicles were prepared from proximal and distal segments of
the large intestine of the rat by a method based on morphological criteria
and were used to determine 22Na uptake. In both preparations an outwardly
directed proton gradient stimulated 22Na uptake. In proximal colon a
decrease in vesicular volume induced by an increased media osmolarity led
to diminished 22Na uptake at 90 min; a significant (50-60%) portion of
uptake represented binding. Initial uptake was linear for 10 s and
extrapolated through zero, indicating minimal extravesicular binding.
Initial uptake was a saturable function of medium Na concentration. In both
preparations initial influx of 0.1 mM NaCl was inhibited by amiloride
(0.1-1.0 mM), 15 mM NaCl, 15 mM LiCl, and 15 mM NH4Cl. From the
characteristics of the initial 22Na influx we conclude that the apical
membrane from colonocytes of proximal and distal segments contains a Na-H
exchange with properties similar to those described in other epithelia.
