Identification of neurotransmitter receptors on Muller cells and their function.

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We obtained previously considerable evidence indicating the expression of AMPA/kainater receptors not only by neurons but also Muller cells. Cytosolic calcium transients following an agonist administration to Muller cells cultured from adult rabbit retinas were examined with spectrofluorometry using fura-2 AM.Calcium transients occurred more in number for neurotoxic kainate exposed that control cells, suggesting the AMPA/kainate receptors develop be novo in pathological state. Using the above methods to detect calcium transients, we found approximately 50% of neurons cultured from neonatal rat retinas responded to muscarine at 50 muM , but 50 muM was requisite for the formation of calcium transients in 50% of cultured Muller cells. The muscarine inducement of calcium transients was blocked by atropine. The agonist of M1, McN-A-343 eliciteed the most significant calcium transients both in neurons and Muller cells. Thus, Muller cells appeared to possess the less sensitive muscarinic receptor including at least M1. P_1-/P_2-purinergic receptor agonists including A2 and P2y induced calcium transients in cultured Muller cells. Muller cells are thus shown guite likely to possess the P_1-/P_2-purinergic receptors. A new excitotoxic amino acid, dysiherbaine is also studied and it induced calcium transients in Muller cells but appeared not to be mediated by known AMPA/Kainate receptors, since the receptor antagonists (CNQX and DNQX) to be mediated by kmown AMPM/Kainate receptors, since the receptor antagonists (CNQX and DNQX) could not block the transients.