Comparison of Sodium Channel Currents Between Various Excitable Cells by Planar Lipid Bilayer and Patch Clamp Methods

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We have been interested in the differences of exitabilities between various exitable cells such as nerve, skeletal muscle and heart muscle cells. So, the single channel currents of Na channels were characterized to compare between the three type of Na channels by using the lipid planar bilayer and patch clamp techniques. Kinetic parameters in blocking of puffer fish toxin, TTX to Na channels were precisely dicided. Na channel of cardiac mucle was the most resistant to TTX. After denervation, skeletal muscle Na channels became as TTX-resistant as heart Na channels. Na channel protein might exist as an isozyme peculiar to each cell type which is easily able to be transformed to the other kind of isozyme. Effects of Na channel activators, batrachotoxin and veratridine on various Na channels were also examined. Every type of Na channel exhibited similar exitabilities then. Thus, these results might explain well the differences and similarities in excitability between various tissues.