Involvement of the Ca2+-dependent K+channel activity in the hyperpolarizing response induced by epidermal growth factor in mammary epithelial cells

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Abstract
Epidermal growth factor (EGF) induces a hyperpolarizing response of 5–20 mV amplitude in mouse mammary epithelial cells in culture. The amplitude of the hyperpolarizing response was reduced by more than 60% within several minutes after addition of blockers of voltage and/or Ca2+‐dependent K+ channels such as tetraethylammonium (7 mM) or quinine (0.29 mM). Both nifedipine (0.15 mM), a blocker of the Ca2+ channel, and ruthenium red (2 mM), an inhibitor of the Ca2+‐binding site, also reduced the amplitude of the hyperpolarizing response by more than 60%. The Ca2+ ionophore, A23187 (3.8 μM), induced a large hyperpolarization, which was 25–40 mV and lasted about 3 min. These data suggest that activity of the Ca2+‐dependent K+ channel was involved in the EGF‐induced hyperpolarizing response of the mammary epithelial cells.