There is now considerable evidence for the involvement of K + channels in nitric oxide (NO) induced relaxation of smooth muscles including the myometrium. In order to assess whether apamin-sensitive K + channels play a role in NO -induced relaxation of the human uterus, we have studied the effect of specific blockers of these channels on the relaxation of myometrium from nonpregnant women. In vitro isometric contractions were recorded in uterine tissues from nonpregnant premenopausal women who

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... ad undergone hysterectomy. Apamin (10 nM) and scyllatoxin (10 nM) did not alter spontaneous myometrial contractions. However, 15-min pretreatment of the myometrium strips with apamin completely inhibited relaxation caused by diethylamine-nitric oxide (DEA/NO). The pretreatment with scyllatoxin significantly reduced (about 2.6 times) maximum relaxation of the strips induced by DEA/NO (p < 0.05). These results strongly suggest that, beside Ca 2+ and voltage dependent charybdotoxin-sensitive (CTX-sensitive) K + channels, apamin-sensitive K + channels are also present in the human non-pregnant myometrium. These channels offer an additional target in the development of new tocolytic agents.