Evidence of K and Ca channels in endothelial cells of human allantochorial placental vessels.

Presence of ionic channels was evaluated in human endothelial cells (ECs) from allantochorial placental vessels by the measure of the membrane potential, the main factor of the excitation-contraction coupling. To characterize endothelial cell channels, vasoactive and vasorelaxant agents and channels blockers were used. In predepolarized cells by high-K+ concentration, the voltage-dependent K+ channels (Kdf) were blocked. Acetylcholine, sodium nitroprusside and isoproterenol hyperpolarized the predepolarized-high K+ ECs. This hyperpolarization was inibited by charybdotoxin (a blocker of big Ca(2+)-activated K+ channels) or/and by tetraethylammonium and was insensitive to glibenclamide (a blocker of ATP-sensitive K+ channels). Serotonin depolarized ECs and the depolarization was inibited by nifedipine, a blocker of voltage-gated Ca2+ channels. These results indicated that membrane potential of human placental allantochorial ECs was regulated by voltage-gated, C(2+)-sensitive K+ channels and by voltage-gated Ca2+ channels.