EFFECT OF DEHYDRATION ON APICAL NA-H+ EXCHANGE ACTIVITY AND NA+-DEPENDENT SUGAR-TRANSPORT IN BRUSH-BORDER MEMBRANE-VESICLES ISOLATED FROM CHICK INTESTINE()

The current work examines the effect of 4 days of water deprivation on Na+-H+ exchange and Na+-sugar cotransport systems in brush-border mem brane vesicles isolated from either the jejunum, ileum or the colon of the chick. Apical Na+-H+ exchange activity was evaluated by measuring the pH-gradient-dependent Na+ uptake. The contribution of the Na+-Hexchangers NHE2 and NHE3 to total Na+-H+ exchange activity was evaluat ed from their sensitivity to the amiloride-related drug HOE694. Dehydr ation increased plasma aldosterone levels from 12 to 70 pg/ml and also the activities of both Na+-H+ exchange and Na+-dependent sugar transp ort in the, three intestinal regions tested. Na+-independent sugar tra nsport was not modified by 4 days of water deprivation. In the ileum a nd colon the increase in Na+-H+ exchange activity was due to an increa se in NHE2 activity, whereas in the jejunum it was due to an increase in both NHE2 and NHE3. Since we have previously reported that chronic Na+ depletion increases plasma aldosterone levels and NHE2 activity in ileum and colon, decreased small and large intestine Na+-sugar cotran sport activity and had no effect on jejunal apical Na+-H+ exchange act ivity, it can be concluded that: (1) aldosterone does not regulate int estinal Na+-dependent sugar transport, and (2) the regulation of jejun al Na+-H+ exchange activity differs from that of either the ileum or t he colon.