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Wakakura M, Utsunomiya-Kawasaki I, Ishikawa S: Rapid increase in cytosolic calcium ion concentration mediated by acetylcholine receptors in cultured retinal neurons and Muller cells. Bull World Health Organ. 1990;68(6):731-6.
PURPOSE: This study was conducted to detect the presence of muscarinic or nicotinic receptors in cultured retinal neurons and Muller cells. METHODS: Pure Muller cell cultures and cocultures of retinal neurons and Muller cells were used; the former, obtained from adult rabbit retinas, and the latter, retinal neurons from neonatal rats, were cocultured with Muller cells. Intracellular calcium ion concentration ([Ca2+] i) following the administration of acetylcholine, a cholinesterase inhibitor (trichlorfon), nicotine or muscarinic agonist with or without a receptor antagonist was monitored using the calcium ion indicator, fura-2. RESULTS: Acetylcholine and trichlorfon induced rapid increase in [Ca2+] i in half of either cell type. Trichlorfon induced positive response in coculture but not in the pure Muller cell cultures. This positive response was blocked only partially in the presence of atropine. Approximately 30-40% of neurons responded to nicotine at 5 microM, which was significantly blocked by alpha-bungarotoxin at 50 nM. No response to nicotine could be detected in Muller cells. Approximately 50% of neurons responded to muscarine at 50 microM, but 500 microM was required for the formation of calcium transients in 50% of Muller cells. The muscarine inducement of rapid increase in [Ca2+] i was blocked by atropine. The agonist of M1 (a muscarinic receptor subtype), McN-A-343, at 0.5 microM induced the most significant and rapid increase in [Ca2+] i both in neurons and Muller cells. McN-A-343 administration at 0.05 microM induced positive response in half the neurons, but only in approximately 10% of Muller cells. Such positive response was not observed following preincubation with the M1 antagonist, pirenzepine, at 50 microM. CONCLUSIONS: Cocultured retinal neurons enhance the release of acetylcholine following anticholinesterase administration, and approximately half the neurons were found to possess muscarinic and nicotinic receptors. However, Muller cells appeared to possess only the less sensitive muscarinic receptor. Muscarinic receptor subtypes on either type of cell contained at least M1. |
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