A CA2-ACTIVATED WHOLE-CELL CL- CONDUCTANCE IN HUMAN PLACENTAL CYTOTROPHOBLAST CELLS ACTIVATED VIA A G-PROTEIN()

Whole-cell patch clamp experiments were performed on cultured human cy totrophoblast cells incubated for 24-48 hr- after their isolation from term placentas. Cl-selective currents were examined using K+-free sol utions. Under nonstimulated conditions, most cells initially expressed only small background leak currents. However, inclusion of 0.2 mM GTP gamma S in the electrode solution caused activation of an outwardly r ectifying conductance which showed marked time-dependent activation at depolarized potentials above +20 mV. Stimulation of this conductance by GTP gamma S was found to be Ca2+-dependent since GTP gamma S failed to activate currents when included in a Ca2+-free electrode solution. In addition, similar currents could be activated by increasing the [C a2+] of the pipette solution to 500 nM. The Ca(2+)activated conductanc e was judged to be Cl-selective, since reversal potentials were predic ted by Nernst equilibrium potentials for Cl-. This conductance could a lso be reversibly inhibited by addition of the anion channel blocker D IDS to the bath solution at a dose of 100 mu M. Preliminary experiment s indicated the presence of a second whole-cell anion conductance in h uman cytotrophoblast cells, which may be activated by cell swelling. P ossible roles for the Ca2+-activated Cl- conductance in human placenta l trophoblast are discussed.