Impairment by cytochalasin B of the inhibitory action of D-mannoheptulose upon D-glucose metabolism in rat pancreatic islets.
D-mannoheptulose was recently found to inhibit D-glucose metabolism in hepatocytes and pancreatic islets, whilst failing to do so in parotid cells, erythrocytes and the exocrine pancreas. In the latter three systems, however, the hexaacetate ester of D-mannoheptulose efficiently inhibits D-glucose metabolism. It was proposed, therefore, that the transport of unesterified D-mannoheptulose into cells may be mediated by GLUT2. Since cytochalasin B is known to inhibit D-glucose transport into pancreatic islet cells, it was now investigated whether the mould metabolite (0.02 mM) also impairs the inhibitory action of D-mannoheptulose (1.0 mM) upon D-glucose metabolism in rat pancreatic islets. The relative extent of D-mannoheptulose inhibitory action on D-[5-3H]glucose utilization and D-[U-14C]glucose conversion to 14CO2, as well as radioactive amino acids and acidic metabolites, was indeed much less marked in the presence of cytochalasin B (13+/-4% inhibition) than in its absence (40+/-3% inhibition). A comparable situation was not observed, however, in the case of glucose-stimulated insulin secretion, cytochalasin B augmenting insulin output to the same relative extent in the absence or presence of D-mannoheptulose. These findings support the view that the entry of D-mannoheptulose into cells may be mediated by a cytochalasin B-sensitive transport system, such as the GLUT2 carrier.
Courtois
P
P
Laboratory of Experimental Medicine, Brussels Free University, Brussels, Belgium.
Sener
A
A
Malaisse
W J
WJ
D000818:Animals; D003571:Cytochalasin B / Q000494:pharmacology*; D005260:Female; D005947:Glucose / Q000378:metabolism*; D051273:Glucose Transporter Type 2; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008356:Mannoheptulose / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D051273:Glucose Transporter Type 2; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D003571:Cytochalasin B; D008356:Mannoheptulose; D005947:Glucose