Differences in glucose transporter gene expression between rat pancreatic α- and β-cells are correlated to differences in glucose transport but not in glucose utilization

Abstract

Glucose exerts inverse effects upon the secretory function of islet α- and β-cells, suppressing glucagon release and increasing insulin release. This diverse action may result from differences in glucose transport and metabolism between the two cell types. The present study compares glucose transport in rat α- and β-cells. β-Cells transcribed GLUT2 and, to a lesser extent, GLUT 1; α-cells contained GLUT1 but no GLUT2 mRNA. No other GLUT-like sequences were found among cDNAs from α- or β-cells. Both cell types expressed 43-kDa GLUT1 protein which was enhanced by culture. The 62- kDa β-cell GLUT2 protein was converted to a 58-kDa protein after trypsin treatment of the cells without detectable consequences upon glucose transport kinetics. In β-cells, the rates of glucose transport were 10- fold higher than in α-cells. In both cell types, glucose uptake exceeded the rates of glucose utilization by a factor of 10 or more. Glycolytic flux, measured as D-[53H]glucose utilization, was comparable in α- and β-cells between 1 and 10 mmol/liter substrate. In conclusion, differences in glucose transporter gene expression between α- and β-cells can be correlated with differences in glucose transport kinetics but not with different glucose utilization rates.