For over a decade we have been characterizing a Maxi Cl^– channel from human placental syncytiotrophoblast apical membrane with distinct biophysical properties: conductance over 200 pS, multiple substates, voltage dependent open probability, and permeation to anionic amino acids. The large unitary conductance and bell-shaped voltage dependence are similar to those of the voltage-dependent anion channel (VDAC) expressed in outer mitochondrial membrane. A growing body of evidence pointing to the expression of VDAC isoforms in the plasma membrane, has suggested that VDAC is the molecular correlate of the Maxi Cl^– channels in many cell types, such as rat astrocytes, PC12 cells and C1300 cells. Recently a Maxi Cl^– channel in C127i cells has also been described to resemble mitochondrial VDAC with respect its dual ATP-conducting and ATP-open channel blocking properties. The aim of this study was to investigate if the Maxi Cl^– channel of human syncytiotrophoblast apical membrane belongs to the VDAC family. The presence of VDAC was demonstrated by confocal microscopy immunocolocalization in apical syncytiotrophoblast membrane of villous trophoblast tissue sections and by Western blotting in purified apical membrane from human placenta. A functional relationship between the apical Maxi Cl^– channel and VDAC was demonstrated using the excised patch electrophysiological technique. We demonstrated that the apical membrane Maxi Cl^– channel, reconstituted in giant liposomes suitable for patch clamp methods, was permeable to ATP (P_ATP/P_Cl = 0.05 ± 0.006, mean ± S.E.M.; n=4) and that the chloride current was also blocked by ATP with a Kd of 11.4 ± 1.8 (mean ± S.E.M.; n=3), results similar to those previously reported in C127i cells. In purified apical membranes reconstituted with and without (control) anti-VDAC antibody, Maxi Cl^–channel activity was detected in 83% of patches in the control condition, but only in 7.7% of patches from liposomes incubated with monoclonal antibodies. Finally, we analysed a human placental cDNA sequence highly homologous to a voltage-dependent anion channel, recently published by NCBI, to search for open reading frames (ORF) in a 5′ sequence upstream of the protein sequence. We identified an ORF that translates a leader sequence peptide determining a secretion pathway for the protein, like that previously described for a mouse VDAC gene. We demonstrated that the human trophoblast expresses a plasmalemmal VDAC isoform by RT-PCR using primers that hybridize to a VDAC sequence coding for an N-terminal leader peptide required for its plasma membrane sorting.