Large-conductance, calcium-activated potassium channel is not involved in either the 4-AP response or spontaneous activity in nonpregnant mouse myometrium. (A) Tissue strips from nonpregnant mice were challenged with 1 mM of the BK blocker TEA. There were no significant differences found between tissue strip contractility in the presence of TEA when compared to spontaneous (no TEA) activity. (B and C) Tissue strips from nonpregnant mice were challenged with 300 μM 4-AP for 5 min, washed for 10 minutes, and then incubated with either iberiotoxin (IbTX, 50 nM, panel B) or verruculogen (100 nM, panel C) for 10 minutes prior to re-challenge with 300 μM 4-AP; the amount of spontaneous contractile activity present in each sample was subtracted from the total activity seen in the presence of either 4-AP or 4-AP plus BK blocker to account for any changes in spontaneous activity. Mean responses in the presence of toxin (A and B) or TEA (C) were not significantly different from those seen in the absence of either toxin or TEA. Results are presented as means ± S.D.; n = 4 for each panel.