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GROWTH, DIFFERENTIATION, AND APOPTOSIS

Acetylcholine induces Ca²⁺ signaling in chicken retinal pigmented epithelial cells during dedifferentiation

¹Department of Cytology and Histology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan; ²iFORCOM, Kanagawa, Japan; and ³Research Institute of Pharmaceutical Sciences, Musashino University, Tokyo, Japan

Submitted 18 August 2008 ; accepted in final form 19 February 2009

Retinal pigmented epithelial cells exchange their cellular phenotypes into lens cells and neurons, via depigmented and non-epithelial-shaped dedifferentiated intermediates. Because these dedifferentiated cells can either revert to pigmented epithelial cells or transdifferentiate into lens cells and/or neurons, they are recognized as candidates for lens and retinal cell regeneration. The purpose of the present study was to elucidate the signal transduction pathways between chicken retinal pigmented epithelial cells and their dedifferentiated intermediates. We monitored intracellular Ca²⁺ concentrations using Fluo-4-based Ca²⁺ optical imaging and focused on cellular responses to the neurotransmitter acetylcholine. Muscarinic Ca²⁺ mobilization was observed both in retinal pigmented epithelial cells and in dedifferentiated cells, and was inhibited by atropine. The muscarine-dependent acetylcholine response depended on Ca²⁺ release from intracellular Ca²⁺ stores, which was completely blocked by thapsigargin. In contrast, the nicotine-dependent acetylcholine response that led to Ca²⁺ influx through L-type Ca²⁺ channels was inhibited by -bungarotoxin and attenuated by nifedipine, and it was detected only in the dedifferentiated intermediates. Application of (S)-(-)-BayK8644 elevated intracellular Ca²⁺ both in retinal pigmented epithelial cells and in dedifferentiated intermediates; however, the nicotinic response was not observed in pigmented epithelial cells. Another L-type Ca²⁺ channel blocker, diltiazem, also blocked the nicotine-dependent acetylcholine response in dedifferentiated cells and maintained the epithelial-like morphology of retinal pigmented epithelial cells. Our results indicate that an alternative acetylcholine signaling pathway is used during the dedifferentiation process of retinal pigmented epithelial cells.

Ca²⁺ optical imaging; Fluo-4; transdifferentiation; nicotinic acetylcholine receptor; L-type Ca²⁺ channel