EFFECT OF CA2-8644 IN HUMAN PLACENTAL ARTERIES( AGONIST BAY K)

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