Expression of functional receptors and transmitter enzymes in cultured Muller cells

Glia represents the most numerous group of nervous system cells and CNS development and function depend on glial cells. We developed a purified Muller glia culture to investigate the expression of several neurotransmitter markers on these cells, such as dopaminergic, cholinergic, GABAergic and peptidergic receptors or enzymes, based on functional assays measuring second messenger levels or Western blot for specific proteins. Purified Muller cell culture was obtained from 8-day-old (E8) embryonic chick. Glial cells cultured for 15 days (E8C15) expressed D1A and D1B receptors mRNAs, but not D1D, as detected by RT-PCR. The binding of [3H]-SCH 23390 revealed an amount of expressed receptors around 40 fmol/mg protein. Dopamine (100 microM), PACAP (50 nM) and forskolin (10 microM) induced a 50-, 30- and 40-fold cAMP accumulation on glial cells, respectively, but not ip3 production. The dopamine-promoted cAMP accumulation was blocked by 2 microM SCH 23390. Carbachol stimulated a 3-fold ip3 accumulation. Western blot analysis also revealed the expression of tyrosine hydroxylase, L-dopa decarboxylase, PAC1 receptor, GAD67 and beta2-nicotinic receptor subunit by these cells. These results indicate that several components of neurotransmitter signaling and metabolism are found in cultured Muller cells.