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 cytotrophoblast cells incubated for 24-48 hr- after their isolation from term placentas. Cl-selective currents were examined using K+-free solutions. 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 rectifying 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 [Ca2+] of the pipette solution to 500 nM. The Ca(2+)activated conductance was judged to be Cl-selective, since reversal potentials were predicted by Nernst equilibrium potentials for Cl-. This conductance could also be reversibly inhibited by addition of the anion channel blocker DIDS to the bath solution at a dose of 100 mu M. Preliminary experiments indicated the presence of a second whole-cell anion conductance in human cytotrophoblast cells, which may be activated by cell swelling. Possible roles for the Ca2+-activated Cl- conductance in human placental trophoblast are discussed.