Early Genesis of Slow Action Potentials in Co-cultured Ectodermal Cells at Different Ages(Developmental Biology)

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Action potentials can be generated in the epidermis of newt (Cynops pyrrhogaster) embryos between Stages 24/25 to 35/36 following the injection of intracellular current pulses. These action potentials consist of two distinct components, a fast spike and a slow action potential. The slow component follows the fast spike and has been shown to be transmitted to other epidermal cells. Cultured presumptive epidermal cells taken from the pregastrula also generate two-step action potentials. The time course of the genesis of the action potential during epidermal differentiation was elucidated by plating the dissociated cells of the presumptive epidermal ectoderm of the pregastrula in close proximity to an older cell colony, known to possess both types of excitability. These preparations, composed of cells in cultures for 2 and 5 days, were used to examine cell to cell transmission of epi dermal potentials via presumed junctions between the colonies. When the epidermis of an older cell was stimulated, the adjacent younger cell, unexcitable electrically, exhibited a slow depolarization under the influence of the older cell. Thus, it appears that the membrane responsible for the genesis of the slow potential may be present before the neurula stage. The mechanism of cell to cell trans mission of the slow action potential is clearly not mediated by electrical transmission; we propose instead that it has a chemical basis.
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