Novel channel-mediated choline transport in cholinergic neurons of the mouse retina

Toshiyuki Ishii, Kohei Homma, Asuka Mano, Takumi Akagi, Yasuhide Shigematsu, Yukio Shimoda, Hiroyoshi Inoue, Yoshihiko Kakinuma, Makoto Kaneda

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2 Citations (Scopus)

Abstract

Choline uptake into the presynaptic terminal of cholinergic neurons is mediated by the high-affinity choline transporter and is essential for acetylcholine synthesis. In a previous study, we reported that P2X2 purinoceptors are selectively expressed in OFF-cholinergic amacrine cells of the mouse retina. Under specific conditions, P2X2 purinoceptors acquire permeability to large cations, such as N-methyl-D-glucamine, and therefore potentially could act as a noncanonical pathway for choline entry into neurons. We tested this hypothesis in OFF-cholinergic amacrine cells of the mouse retina. ATP-induced choline currents were observed in OFF-cholinergic amacrine cells, but not in ON-cholinergic amacrine cells, in mouse retinal slice preparations. High-affinity choline transporters are expressed at higher levels in ON-cholinergic amacrine cells than in OFF-cholinergic amacrine cells. In dissociated preparations of cholinergic amacrine cells, ATP-activated cation currents arose from permeation of extracellular choline. We also examined the pharmacological properties of choline currents. Pharmacologically, α,β-methylene ATP did not produce a cation current, whereas ATPγS and benzoyl-benzoyl-ATP (BzATP) activated choline currents. However, the amplitude of the choline current activated by BzATP was very small. The choline current activated by ATP was strongly inhibited by pyridoxalphosphate-6-azophe-nyl-2′,4′-sulfonic acid. Accordingly, P2X2 purinoceptors expressed in HEK-293T cells were permeable to choline and similarly functioned as a choline uptake pathway. Our physiological and pharmacological findings support the hypothesis that P2 purinoceptors, including P2X2 purinoceptors, function as a novel choline transport pathway and may provide a new regulatory mechanism for cholinergic signaling transmission at synapses in OFF-cholinergic amacrine cells of the mouse retina. NEW & NOTEWORTHY Choline transport across the membrane is exerted by both the high-affinity and low-affinity choline transporters. We found that choline can permeate P2 purinergic receptors, including P2X2 purinoceptors, in cholinergic neurons of the retina. Our findings show the presence of a novel choline transport pathway in cholinergic neurons. Our findings also indicate that the permeability of P2X2 purinergic receptors to choline observed in the heterologous expression system may have a physiological relevance in vivo.

Original languageEnglish
Pages (from-to)1952-1961
Number of pages10
JournalJournal of Neurophysiology
Volume118
Issue number4
DOIs
Publication statusPublished - 2017 Oct 1

Keywords

  • Cholinergic neuron
  • P2X purinoceptor
  • Retina

ASJC Scopus subject areas

  • Neuroscience(all)
  • Physiology

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    Ishii, T., Homma, K., Mano, A., Akagi, T., Shigematsu, Y., Shimoda, Y., Inoue, H., Kakinuma, Y., & Kaneda, M. (2017). Novel channel-mediated choline transport in cholinergic neurons of the mouse retina. Journal of Neurophysiology, 118(4), 1952-1961. https://doi.org/10.1152/jn.00506.2016