Ca 2+ entry through L-type voltage-sensitive Ca 2+ channels stimulates the release of human chorionic gonadotrophin and placental lactogen by placental explants

Abstract

The release of human chorionic gonadotrophin (hCG) and placental lactogen (hPL) by human placental explants can be stimulated by Ca 2+ entry. The aim of the present study was to characterize the modality of Ca 2+ entry in the presence of high extracellular K + concentration ([K +] o). A rise in [K +] o from 5 to ≧ 50 mM induced a rapid and marked increase in the release of hCG and hPL from human term placental explants. The stimulatory effects of an excess [K +] o on the release of hCG and hPL were blocked in the absence of extracellular Ca 2+ or in the presence of 0.5 mM Co 2+. The presence of 50 μM methoxyverapamil, 20 μM nifedipine or 40 μM Cd 2+ in the medium inhibited the stimulatory effects of [K +] o addition. Lastly, 40 μM Ni 2+ failed to affect the increases in hCG and hPL releases elicited by [K +] o addition. Our data clearly show that a rise in [K +] o stimulates the release of hCG and hPL from placental explants. These secretory effects can be viewed as resulting from a Ca 2+ entry through voltage-sensitive Ca 2+ channels of the L-type.