The coexistence in rat muscle cells of two distinct classes of Ca2+-dependent K+ channels with different pharmacological properties and different physiological functions.

Ca2+-dependent K+ channels responsible for the long-lasting after-hyperpolarization in rat muscle cells in culture are not those extensively studied by the patch-clamp technique. The first ones are blocked by apamin, a bee venom polypeptide, and they are unaffected by tetraethylammonium (TEA) whereas the second ones are blocked by TEA and unaffected by apamin. These two Ca2+-dependent K+ channels coexist in rat muscle cells in culture but also probably in many other cellular types.