Properties of two multisubstate Cl- channels from human syncytiotrophoblast reconstituted on planar lipid bilayers

• Published in: The Journal of membrane biology Vol. 157; no. 1; pp. 83 - 95
• Main Authors: Grosman, C, Mariano, M I, Bozzini, J P, Reisin, I L
• Format: Journal Article
• Language: English
• Published: United States Springer Nature B.V 01.05.1997
• Subjects: Cations; Centrifugation; Channel gating; Chloride Channels - metabolism; Chorionic Villi - metabolism; Chorionic Villi - ultrastructure; Fluorescent indicators; Homeostasis; Humans; Ion channels; Ion transport; Ions; Lipid Bilayers; Lipids; Magnesium; Membrane potential; Membranes; Microelectrodes; Patch-Clamp Techniques; Permeability; Trophoblasts - metabolism
• ISSN: 0022-2631; 1432-1424
• DOI: 10.1007/s002329900218

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 voltage-dependent, 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.