SIMULTANEOUS MEASUREMENT OF CA-45 OUTFLOW AND HUMAN PLACENTAL-LACTOGEN RELEASE FROM PLACENTAL EXPLANTS

Kinetics of Ca-45 outflow and human placental lactogen (hPL) release w ere characterized in human placental explants. Measurements of the rat e of Ca-45 and [H-3]-sucrose (extracellular space marker) outflow from preloaded explants showed that, after a 40 min washout period, the Ca -45 effluent radioactivity presumably originated from an intracellular compartment. This view was further supported by the La3+ and temperat ure sensitivity of the Ca-45 outflow. Moreover, the addition of ionomy cin as well as an increase in the extracellular Ca2+ or Ba2+ concentra tion provoked a dose-dependent rise in both the Ca-45 outflow and hPL release. There were no systematic temporal analogies between the patte rn of Ca-45 outflow and hPL release. Taken together, these observation s suggest that the stimulation of Ca-45 outflow reflects an increased rate of Ca-40 entry. The present data also extend previous observation s indicating that hPL release can be stimulated by Ca2+ entry, Lastly, the 'in vitro' method described herein allows one to compare rapid ch anges in hPL release with associated ionic events and can be used to f urther document the relationships between placental secretory response s and cell calcium metabolism.