Effects of hyperglycemia and protein kinase C on Connexin43 expression in cultured rat retinal pigment epithelial cells

Previous results demonstrated that the intercellular communication mediated by gap junctions in retinal pigment epithelial (RPE) cells from the health y Long Evans (LE) rat strain is higher than that from the dystrophic Royal College of Surgeons (RCS) rat strain. We examined connexin (Cx) expression in both cell types. At the mRNA level, a qualitatively similar expression p attern was found whereby Cx26, Cx32, Cx36, Cx43, Cx45 and Cx36 were all exp ressed. At the protein level, only Cx43 and Cx36 were detected. Expression of both isoforms was higher in LE-RPE as compared to RCS-RPE by a factor of 1.25 and 2 respectively. Phosphorylation of Cx43 was increased upon activa tion of protein kinase C (PKC) by 1 muM phorbol 12-myristate 13-acetate (PM A). The phosphorylation status was not changed in hyperglycemic conditions, but this treatment strongly decreased total Cx43 levels to about 75 and 40 % tin LE-RPE and RCS-RPE cells respectively) of the control level in LE-RPE cells. This decrease could be overcome by PKC downregulation. These result s demonstrate that PKC activation and hyperglycemic conditions have differe nt effects on Cx43 and that PKC is involved in the metabolic pathway induce d by hyperglycemic conditions.