EXPRESSION OF GLUCOSE TRANSPORTERS IN HUMAN PERITONEAL MESOTHELIAL CELLS

Glucose containing solutions, the basis of peritoneal dialysis fluids, affect the proliferation and regeneration of peritoneal mesothelial c ells (MsC). The aim of this study was to examine mechanisms of glucose transport into MsC, that is, the expression of facilitative glucose t ransporters (GLUT) and the Na(+)-dependent glucose transporter (SGLT1) in human primary MsC and a transfected MsC line. Since expression of both transporters is differentiation dependent, we investigated the ef fects of cell differentiation induced by culturing MsC on membranes or by addition of hexamethylene bisacetamide (HMBA; 6 mM), which enhance s SGLT1 expression in LLC-PK1 cells. Levels of mRNA for GLUT1 through GLUT-4 and SGLT1 were evaluated by reverse transcriptase-polymerase ch ain reaction (RT-PCR). The presence of the corresponding proteins was examined by Western blotting and localized by immunofluorescence. Acti ve. Na(+)-dependent glucose transport was assessed by alpha-methyl-D-[ C-14]glucopyranoside (AMG) with and without the SGLT1-specific inhibit or phlorizin and by patch clamp experiments in NaCl or choline-chlorid e. For Na(+)dependent glucose uptake choline chloride instead of NaCl served as negative control. Facilitative transport was assessed using 2-fluoro-2-deoxy[C-14]-D-glucose (FDG) dth and without the inhibitors cytochalasin B or phloretin. Primary and transfected MsC express GLUT1 and GLUT3 mRNA while no transcripts were found for GLUT2 and GLUT4. N o SGLT1 transcript was detectable in subconfluent cells. Semiquantitat ive RT-PCR analysis documented that the addition of the differentiatio n inducer HMBA to confluent cultures or growth of MsC on membranes for seven days produced a down-regulation of mRNA for GLUT1, no change fo r GLUT3, and a substantial increase for SGLT1 mRNA. Under these condit ions MsC express SGLT1 protein and possess a Na(+)-dependent glucose u ptake as assessed by AMG. Phlorizin (1 mM) inhibits AMG uptake by 30 t o 45%. In patch clamp experiments the addition of extracellular glucos e depolarized the membrane potential only in the presence of sodium. T hese results indicate that differentiated MsC express GLUT1, GLUT3, an d SGLT1. Further characterization of these transport mechanisms and th eir regulation may help to understand the cellular effects of glucose on MsC in peritoneal dialysis.