MODULATION OF VEGF PRODUCTION BY PH AND GLUCOSE IN RETINAL MULLER CELLS

Purpose. To investigate the influence of pH and glucose concentration, both of which represent significant biochemical variables in tissue i schemia, on the production of VEGF protein by retinal Muller cells and C6 glioma cells, under normoxic and hypoxic conditions. Methods. Rat retinal Muller cells and C6 glioma cells grown in tissue culture monol ayers were studied. The effect of pH (range 7.0-8.0) and glucose conce ntration (0.6-25 mmol/L) on VEGF protein production, under both normox ic and hypoxic conditions, were evaluated by ELISA analysis of the con ditioned media. Establishment of significant cell hypoxia was verified by measurement of lactate release into the conditioned media. Results . Hypoxia caused a 7.9-fold increase in VEGF production in C6 cells at 24 h, and a 3.4-fold increase in Muller cells after 48 h. Under hypox ic conditions, VEGF protein production was increased further by increa sing pH and increasing glucose, and decreased by low pH and low glucos e. Varying the glucose concentration or pH of the medium did not resul t in significant induction of VEGF protein production by either cell t ype under normoxic conditions. Conclusions. Both glucose and pH signif icantly affected VECF production induced by low oxygen. However, neith er exerted a measurable stimulatory effect on VEGF production in normo xic conditions. Coexisting hypoxia and acidosis or hypoglycemia, as mi ght occur in severe tissue ischemia, may render glial cells incapable of effectively upregulating VEGF synthesis, while alkalosis or hypergl ycemia may augment hypoxia-induced VEGF production.