REGULATION OF GLUCOSE-TRANSPORT AND EXPRESSION OF GLUT3 TRANSPORTERS IN HUMAN CIRCULATING MONONUCLEAR-CELLS - STUDIES IN CELLS FROM INSULIN-DEPENDENT DIABETIC AND NONDIABETIC INDIVIDUALS

We have previously shown that human circulating mononuclear cells (CMCs) respond to physiological concentrations of insulin with a rapid increase in glucose transport rate. The responding cells were found to be the monocytes, and cells derived from individuals with insulin-dependent diabetes mellitus (IDDM) had lower basal and insulin-stimulated glucose transport rates. Of interest, both cell types were found to express the GLUT1 but not the typical insulin-responsive GLUT4 transporter isoform. To further study the mechanisms responsible for stimulation of transport in these cells, we investigated (1) the response to insulin-like growth factor-I (IGF-I) and insulin-mimetic agents, and (2) the expression of other glucose transporter isoforms in CMCs of nondiabetic and IDDM individuals. The time course of insulin-stimulated glucose uptake in CMCs was rapid, reaching a plateau within 30 minutes. CMCs showed a dose-dependent and highly sensitive increase in glucose uptake to IGF-I (maximal response reached at 0.1 to 0.5 nmol/L IGF-I). The IGF-I dose-response curve was similar for CMCs of control and IDDM individuals, but both the basal and maximal response to IGF-I were lower in the diabetic group (P < .01). CMCs did not respond to vanadate, lithium, hydrogen peroxide, or short incubation (1 hour) with metformin, but glucose uptake increased in response to peroxides of vanadate and longer-duration (14 hours) metformin incubations. The glucose transporter isoforms of separated monocytes and lymphocytes were further investigated by Northern blotting of total RNA with a GLUT3-specific cDNA probe and by Western blotting of total membranes using GLUT3-specific antiserum. Both cell types expressed substantial amounts of GLUT3 mRNA and protein, with significantly more GLUT3 protein in monocytes than in lymphocytes. The results indicate that (1) insulin-mimetic agents active in adipocytes are not uniformly effective in CMCs, (2) CMCs from IDDM individuals show suboptimal maximal response to IGF-I, and (3) insulin-mediated glucose transport in these cells may occur via GLUT1 and/or GLUT3 transporters, but neither isoform is reduced in monocytes or lymphocytes of individuals with IDDM. © 1994.