We describe the first successful reconstitution of placental ionic channels on planar lipid bilayers. An apical plasma membrane-enriched vesicle fraction from human syncytiotrophoblast at term was prepared by following isotonic agitation, differential centrifugation, and Mg2+-induced selective precipitation of nonapical membranes, and its purity was assessed by biochemical and morphological marker analysis. We have already reported that, unlike previous patch-clamp studies, nonselective cation channels were incorporated in most cases, a result consistent with the higher permeability for cations as compared with Cl− and with the low apical membrane potential difference at term revealed by fluorescent probe partition studies, and microelectrode techniques. In this paper, we report that Cl−-selective channels were incorporated in 4% of successful reconstitutions (14 out of 353) and that their analysis revealed two types of activity. One of them was consistent with a voltagedependent, 100-pS channel while the other was consistent with the lateral association of 47-pS conductive units, giving rise to multibarrelled, DIDS-sensitive channels of variable conductance (300 to 650 pS). The latter displayed a very complex behavior which included cooperative gating of conductive units, long-lived substates, voltage-dependent entry into an apparent inactivated state, and flickering activity. The role of the reported Cl− channels in transplacental ion transport and/or syncytium homeostasis remains to be determined.
The Journal of Membrane Biology – Springer Journals
Published: Mar 31, 2009
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