In mouse mammary epithelial cells in primary culture, mechanical stimulation of a cell induced in other cells within the same colony a short depolarization of less than 15 m V with a duration of 1–8 s and a subsequent, prominent hyperpolarization of 6 m V lasting 10–40 s. Epidermal growth factor induces a spontaneous hyperpolarizing response in cultured mammary cells, and in cells treated with EGF mechanical stimulation produced a greater hyperpolarization, while the amplitude of the depolarizing response was not affected. The amplitude of the mechanically induced hyperpolarization was markedly reduced by quinine and tetraethylammonium, blockers of the Ca2+-dependent K+ channel. The results suggest that the Ca2+-dependent K+ channel was involved in the hyperpolarization.
