D-mannoheptulose uptake and its metabolic and secretory effects in human pancreatic islets

D-mannoheptulose was recently proposed to be transported into cells at the intervention of GLUT2. Since GLUT1, rather than GLUT2, represents the major carrier system for the transport of monosaccharides across the islet B-cel l plasma membrane in human subjects, the uptake of D-mannoheptulose and its metabolic and secretory effects were investigated in human islets. The upt ake of D-glucose reached much more rapidly a close-to-equilibrium value in isolated islets than in pieces of pancreas obtained from the same donor. Th e distribution space of D-[H-3]mannoheptulose in the human islets largely e xceeded that of [U-C-14]sucrose, considered as an extracellular marker, and did not differ significantly from that of (HOH)-H-3. In the human islets, the heptose (10.0 mM) inhibited both D-[5-H-3]glucose utilization and D-[U- C-14] glucose oxidation, and decreased glucose-stimulated insulin release t o the same extent as D-mannoheptulose hexaacetate. These findings indicate that a suitable radioactive analog of D-mannoheptulose could be used, in hu man like in rat islets, for preferential labelling of the endocrine moiety of the pancreatic gland.