Effect of Ca2+ agonist Bay K 8644 in human placental arteries

1. Bay K 8644 (0.1 microM induced weak contractions in human placental artery segments that were increased in the presence of 7.5 mM K+. K+ and serotonin (5-HT) induced contractions that were enhanced by preincubation of segments with Bay K 8644. These enhancements were reduced by nifedipine (0.1 microM) and diltiazem (1 microM). 2. Bay K 8644 induced a 45Ca2+ uptake increase which was potentiated by depolarization with K+ (less than 30 mM) and antagonized by nifedipine. K+ (15 and 30 mM) and 5-HT (1 microM) induced 45Ca2+ uptake that was enhanced by Bay K 8644. 3. These results suggest that Bay K 8644: (1) is unable to activate the quiescent potential-operated Ca2+ channels (POCs) of these arteries, and (2) activates receptor (5-HT)-operated Ca2+ channels or facilitates Ca2+ influx through POCs activated by 5-HT.