Abstract
1. In segments of human placental veins precontracted with K + (25, 40 or 75 mM), diltiazem produced concentration-dependent relaxations with similar EC 50 values. 2. Diltiazem (20 min preincubations) also caused concentration-dependent inhibition of the contractions induced by K + (40 or 75 mM) and 5-HT (serotonin, 3 × 10 −7 M). IC 50 values were similar, in both cases. 3. The time-course of the vasocontractions induced by 75 mM K + and 3 × 10 −7 M 5-HT in the absence and in the presence of diltiazem were different. The contractions caused by K + were sustained and transient those elicited by 5-HT. 4. These data suggest that (1) this vasculature is sensitive to diltiazem, and (2) the Ca influx through voltage-operated Ca channels (activated by K +) and through receptor-operated Ca channels (activated by 5-HT) is very similar.
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