HIGH GLUCOSE-INDUCED MESANGIAL CELL ALTERED CONTRACTILITY - ROLE OF THE POLYOL PATHWAY

Glomerular mesangial cells cultured in high glucose conditions display impaired contractile responsiveness. It was postulated that glucose m etabolism through the polyol pathway leads to altered mesangial cell c ontractility involving protein kinase C. Rat mesangial cells were grow th-arrested for 24 h with 0.5% fetal bovine serum in either normal (5. 6 mmol/l) or high (30 mmol/l) glucose concentrations or high glucose p lus the aldose reductase inhibitor, ARI-509 (100 mu mol/l). The reduct ion of cell planar surface area (contraction) in response to endotheli n-l (0.1 mu mol/l), or to phorbol 12-myristate 13-acetate (50 pmol/l), was studied by videomicroscopy. In response to endothelin-l, mesangia l cells in normal glucose contracted to 52 +/- 3 % of initial planar a rea. In high glucose, the significantly (p < 0.05) smaller cell size a nd no contractile responsiveness to endothelin-l were normalized with ARI-509. Membrane-associated diacylglycerol, measured by a kinase spec ific P-32-phosphorylation assay, in high glucose was unchanged after 3 h, but significantly increased (p < 0.05) after 24 h which was normal ized with ARI-509. Protein kinase C activity, measured by in situ P-32 -phosphorylation of the epidermal growth factor receptor substrate was . increased by 32 % at 3 h of high glucose, unchanged by ARI-509; and decreased significantly (p < 0.05) at 24 h compared to cells in normal glucose, normalized by ARI-509. Total cellular protein kinase C-alpha , -delta and -epsilon, analysed by immunoblotting, were unchanged in h igh glucose at 24 h. Only protein kinase C-epsilon content was reduced by ARI-509 in both normal and high glucose. Therefore, high glucose-i nduced loss of mesangial cell contractility, diacylglycerol accumulati on and altered protein kinase C activity are mediated through activati on of the polyol-pathway, although no specific relationship between el evated diacylglycerol and protein kinase C activity was observed. In h igh glucose, altered protein kinase C function, or another mechanism r elated to the polyol pathway, contribute to loss of mesangial cell con tractile responsiveness.