Development of ionic channels during mouse neuronal differentiation

Using a mouse embryonal teratocarcinoma (E.C.) cell line, it was possible to follow the sequence of development of ionic channels during neuronal differentiation, with patch-clamp techniques. 1003 E.C. cells were induced to differentiate into neurons by culturing them in defined medium without foetal calf serum (Darmon et al., 1981). Non-differentiated cells were not excitable and presented mainly 2 types of K⁺ channels: a Ca²⁺ activated K⁺ channel (220 pS in symmetrical K⁺) and a delayed rectifier (30 pS in symmetrical K⁺). When the cells start to grow neurites, a low threshold calcium current can be recorded, only if the cell is held at hyperpolarized potentials (- 70 to - 80 mV). Fully differentiated cells with long neurites presented a complete repertoire of ionic channels: voltage dependent Na⁺ and Ca²⁺ channels, Ca²⁺ activated K⁺ channel and K⁺ delayed rectifier.