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The Journal of Neuroscience, January 28, 2004, 24(4):886-894; doi:10.1523/JNEUROSCI.3676-03.2004

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Cellular/Molecular
Molecular Basis of Gap Junctional Communication in the CNS of the Leech Hirudo medicinalis

Iain M. Dykes, Fiona M. Freeman, Jonathan P. Bacon, and Jane A. Davies

Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom

Gap junctions are intercellular channels that allow the passage of ions and small molecules between cells. In the nervous system, gap junctions mediate electrical coupling between neurons. Despite sharing a common topology and similar physiology, two unrelated gap junction protein families exist in the animal kingdom. Vertebrate gap junctions are formed by members of the connexin family, whereas invertebrate gap junctions are composed of innexin proteins. Here we report the cloning of two innexins from the leech Hirudo medicinalis. These innexins show a differential expression in the leech CNS: Hm-inx1 is expressed by every neuron in the CNS but not in glia, whereas Hm-inx2 is expressed in glia but not neurons. Heterologous expression in the paired Xenopus oocyte system demonstrated that both innexins are able to form functional homotypic gap junctions. Hm-inx1 forms channels that are not strongly gated. In contrast, Hm-inx2 forms channels that are highly voltage-dependent; these channels demonstrate properties resembling those of a double rectifier. In addition, Hm-inx1 and Hm-inx2 are able to cooperate to form heterotypic gap junctions in Xenopus oocytes. The behavior of these channels is primarily that predicted from the properties of the constituent hemichannels but also demonstrates evidence of an interaction between the two.

This work represents the first demonstration of a functional gap junction protein from a Lophotrochozoan animal and supports the hypothesis that connexin-based communication is restricted to the deuterostome clade.

Key words: connexin; electrical synapse; gap junction; Hirudo medicinalis; innexin; leech; neuronal-glial communication; Xenopus oocytes

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Received Aug 6, 2003; revised October 29, 2003; accepted October 30, 2003.

This article has been cited by other articles:

				L. Rela and L. Szczupak In Situ Characterization of a Rectifying Electrical Junction J Neurophysiol, February 1, 2007; 97(2): 1405 - 1412. [Abstract] [Full Text] [PDF]

				M. T. Barbe, H. Monyer, and R. Bruzzone Cell-Cell Communication Beyond Connexins: The Pannexin Channels Physiology, April 1, 2006; 21(2): 103 - 114. [Abstract] [Full Text] [PDF]

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