Stimulation of fructose transport across the intestinal brush-border membrane by PMA is mediated by GLUT2 and dynamically regulated by protein kinaseC

Perfusion of rat jejunum in vitro with PMA increased fructose transport by 70 % compared with control values and was blocked by the protein kinase C ( PKC) inhibitor chelerythrine. The brush-border membrane contained both the fructose transporters GLUT5 and GLUT2; the presence of the latter was confi rmed by luminal biotinylation. PMA increased the GLUT2 level 4-fold within minutes, so that the level was comparable with that of the basolateral memb rane, but had no effect on GLUT5 level. GLUT2 was functional, accessible to luminal fructose and could be inhibited selectively by phloretin to permit determination of GLUT2- and GLUT5-mediated transport components. The 4-fol d increase in GLUT2 level induced by PMA was matched by a 4-fold increase i n GLUT2-mediated transport: there was a compensatory fall in the GLUT5-medi ated rate. The pattern of dynamic trafficking was seen only for GLUT2, not GLUT5 or SGLT1, implying that GLUT2 trafficks to the brush-border membrane by a different pathway. Trafficking of GLUT2 to the brush-border membrane c orrelated with activation of PKC beta II, implying that this isoenzyme is l ikely to control trafficking. Since PKC is activated by endogenous hormones , GLUT2 levels in vivo are 3-4-fold those in vitro; moreover, because PKC i s inactivated as soon as intestine is excised, GLUT2 is lost from the brush -border within minutes in vitro. It is therefore difficult to detect GLUT2 in most ill vitro preparations and its role in intestinal sugar absorption across the brush-border membrane has accordingly been overlooked.