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An intracellular P2X receptor required for osmoregulation in Dictyostelium discoideum

Abstract

P2X receptors are membrane ion channels gated by extracellular ATP1,2 that are found widely in vertebrates, but not previously in microbes. Here we identify a weakly related gene in the genome of the social amoeba Dictyostelium discoideum, and show, with the use of heterologous expression in human embryonic kidney cells, that it encodes a membrane ion channel activated by ATP (30–100 μM). Site-directed mutagenesis revealed essential conservation of structure–function relations with P2X receptors of higher organisms. The receptor was insensitive to the usual P2X antagonists3 but was blocked by nanomolar concentrations of Cu2+ ions. In D. discoideum, the receptor was found on intracellular membranes, with prominent localization to an osmoregulatory organelle, the contractile vacuole. Targeted disruption of the gene in D. discoideum resulted in cells that were unable to regulate cell volume in hypotonic conditions. Cell swelling in these mutant cells was accompanied by a marked inhibition of contractile vacuole emptying. These findings demonstrate a new functional role for P2X receptors on intracellular organelles, in this case in osmoregulation.

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Figure 1: Dd P2X receptor is an ATP-gated ion channel.
Figure 2: Properties of Dd P2X receptors.
Figure 3: Dd P2X receptors are localized to the contractile vacuole and are required for cell volume regulation and contractile vacuole voiding.

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Acknowledgements

We thank H. Broomhead, L. Almond, K. Dossi and N. Aldren for their technical expertise during this study, and A. Mueller-Taubenberger for the gift of the pDEX 27 GFP vector. This work was supported by the Wellcome Trust, the Medical Research Council and the Lister Institute of Preventive Medicine.

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Correspondence to Christopher R. L. Thompson or R. Alan North.

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Fountain, S., Parkinson, K., Young, M. et al. An intracellular P2X receptor required for osmoregulation in Dictyostelium discoideum. Nature 448, 200–203 (2007). https://doi.org/10.1038/nature05926

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