Diverse calcium channel types are present in the human placental syncytiotrophoblast basal membrane

Abstract

The functional expression of calcium channels has been scarcely studied in human placental syncytiotrophoblast. We have presently sought to characterize Ca(2+) currents of the healthy syncytiotrophoblast basal membrane using purified basal membranes reconstituted in giant liposomes subjected to patch-clamp recordings. We detected presence of channels with high permeability to Ca(2+) (relative PCa/PK up to 99.5) using K(+) solutions in symmetric conditions. Recordings performed in Ba(2+) gradients showed Ba(2+)-conducting channels in 100% of experiments. Ba(2+) total patch currents were consistently blocked by addition of NiCl(2), Nifedipine (L-type voltage-gated calcium channel blocker) or Ruthenium Red (TRPV5-TRPV6 channel blocker); Nifedipine and Ruthenium Red exerted a synergic blocking effect on Ba(2+) total patch currents. Immunohistochemistry of placental villi sections evidenced presence of alpha(1) subunit of voltage-gated calcium channels and TRPV5-TRPV6 channels in basal and apical syncytiotrophoblast plasma membranes; these three calcium channels were also detected in purified basal and apical fractions using Western blot. These results show the presence of three types of calcium channels in the syncytiotrophoblast basal membrane by both functional and molecular means. These basal membrane calcium channels would not be directly involved in mother-to-fetus Ca(2+) transport, but could participate in other relevant trophoblast processes, such as exocytosis and Ca(2+) transport regulation.