The evolution of ion channels
The early years (1945-1970) revealed that ion channels were aqueous pores on nerve and muscle plasma membranes. Seminal work by Sir Alan L. Hodgkin and Andrew F. Huxley in the 1950s using the accessible preparations of the giant axons from Atlantic squids, introduced the world to the properties of voltage-gated sodium and potassium channels using the voltage-clamp technique. Bernard Katz and colleagues followed with the first detailed description of ligand gated currents active by acetylcholine at the frog neuromuscular junction in the 1960s. Using different animal preparations, a wide spectrum of different ion channels and their properties have been described, in native cells and tissues by electrophysiological recording. A revolution in molecular techniques began in the 1980s and picked up steam in the 1990s, which allowed for the readout of isolated ion channel genes in surrogate cells, such as frog (Xenopus) oocytes, as injected mRNA run-off transcripts or transfection of genes in human cell lines, such as HEK293 cells. Faster and more sensitive molecular screening methods, especially the use of polymerase chain reaction (PCR), allowed the quick functional characterization of cloned ion channels from any tissue source using a range of different species. The complete array of ion channels became attainable for a single species, with the first genome sequencing in the late 1990s, including the smaller animal genomes that were model genetic organisms, such as nematode C. elegans and fruit fly, Drosophila melanogaster, and then the full human genome by 2003. The complete genome sequencing of any life form is now available for hundreds of dollars instead of millions, and on a table-top unit by a single user, instead of a mass consortium of hundreds of contributors that were required for the human genome sequencing project to be completed. Both the variety in structures and functions for ion channels can be understood in the broad phylogenetic context, which includes prokaryotes, which harbor distant relatives of many eukaryotic genes. Many ion channels have a clear-cut ancestry within single cell eukaryotes, with lineages extending through multicellular species within algae, plants and animals. Loss and gains, and adaptations in the complement of Ion channels are observed from single celled animals, to multicellular organisms, through different animal body plans, through the protostomes and deuterostomes. Ion channels are a favorite target for peptide toxins derived from venomous animals, and there are many examples of predator and prey adaptations to channel toxin warfare. The Research Topic of “Evolution of Ion Channels” within Frontiers provides a forum for presentation, debate, and fertilization of further experimentation and analyses, in all aspects of ion channel evolution, using techniques of inquiry such as bioinformatics, electrophysiology, structure-function and mutational analyses, biochemistry, microscopic imaging and X-ray crystallography.
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International Journal of Pure and Applied Zoology