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First published online February 27, 2009
Journal of Experimental Biology 212, 761-767 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026971
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Expression of a poriferan potassium channel: insights into the evolution of ion channels in metazoans

Gabrielle J. Tompkins-MacDonald1, Warren J. Gallin1, Onur Sakarya2,*, Bernard Degnan3, Sally P. Leys1 and Linda M. Boland4,{dagger}

1 University of Alberta, Department of Biological Sciences, Edmonton, AB, Canada T6G 2E9
2 University of California, Neuroscience Research Institute, Santa Barbara, CA 93117, USA
3 School of Integrative Biology, University of Queensland, Brisbane 4072, Australia
4 University of Richmond, Department of Biology, Richmond, VA 23173, USA

{dagger} Author for correspondence (e-mail: lboland{at}richmond.edu)

Accepted 15 December 2008

Ion channels establish and regulate membrane potentials in excitable and non-excitable cells. How functional diversification of ion channels contributed to the evolution of nervous systems may be understood by studying organisms at key positions in the evolution of animal multicellularity. We have carried out the first analysis of ion channels cloned from a marine sponge, Amphimedon queenslandica. Phylogenetic comparison of sequences encoding for poriferan inward-rectifier K+ (Kir) channels suggests that Kir channels from sponges, cnidarians and triploblastic metazoans each arose from a single channel and that duplications arose independently in the different groups. In Xenopus oocytes, AmqKirA and AmqKirB produced K+ currents with strong inward rectification, as seen in the mammalian Kir2 channels, which are found in excitable cells. The pore properties of AmqKir channels demonstrated strong K+ selectivity and block by Cs+ and Ba2+. We present an original analysis of sponge ion channel physiology and an examination of the phylogenetic relationships of this channel with other cloned Kir channels.

Key words: Kir, evolution, inwardly rectifying, ion channel, metazoa, sponge


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