Apical Maxi-chloride channel from human placenta: 12 years after the first electrophysiological recordings.

The Maxi-chloride channel was the first ion channel described by electrophysiological methods in placenta. Because it is difficult to access a complex epithelium such as the placenta for electrophysiological procedures, the studies of ion channels from placental membranes have been performed only very recently. It was only in 1993 that a direct demonstration of a high-conductance chloride channel in apical membranes of intact trophoblastic epithelium was mentioned, and two years later, the description of this channel was reported from purified placental apical membranes reconstituted into artificial lipid membranes suitable for patch-clamp recordings. This brief review comments on the work done with regard to the electrophysiological characterization and regulation of the large-conductance or "Maxi" chloride channel and its contribution to the development of a cellular model for syncytiotrophoblast ion transport.