title: Calcium transport and local pool regulate polycystin-2 (TRPP2) function in human syncytiotrophoblast.
abstract: Polycystin-2 (PC2, TRPP2) is a Ca(2+)-permeable, nonselective cation channel implicated in Ca(2+) transport and epithelial cell signaling. Although PC2 may contribute to Ca(2+) transport in human term placenta, the regulatory mechanisms associated with Ca(2+) handling in this tissue are largely unknown. In this work we assessed the regulation by Ca(2+) of PC2 channel function from a preparation of apical membranes of human syncytiotrophoblast (PC2hst) reconstituted in a lipid bilayer system. Addition of either EGTA or BAPTA to the cis hemi-chamber, representing the cytoplasmic domain of the channel, and lowering Ca(2+) to ∼0.6-0.8 nM, inhibited spontaneous PC2hst channel activity, with a time response dependent on the chelator tested. EGTA reduced PC2hst channel currents by 86%, with a t1/2 = 3.6 min, whereas BAPTA rapidly and completely (100%) eliminated channel activity with a t1/2 = 0.8 min. Subsequent titration with Ca(2+) reversed the inhibition, which followed a Hill-type function with apparent dissociation constants of 1-5 nM, and 4 Ca(2+) binding sites. The degree of inhibition by the cis Ca(2+) chelator largely depended on increasing trans Ca(2+). This was consistent with measurable Ca(2+) transport through the channel, feeding the regulatory sites in the cytoplasmic domain. Interestingly, the reconstituted in vitro translated PC2 (PC2iv) was completely insensitive to Ca(2+) regulation, suggesting that the regulatory sites are not intrinsic to the channel protein. Our findings demonstrate the presence of a Ca(2+) microdomain largely accessible through the channel that controls PC2 function in human syncytiotrophoblast of term placenta.
authors.affiliation: Cátedra de Biofísica, Facultad de Odontología, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: María Del Rocío
authors.initials: Mdel R
authors.lastname: Cantero
authors.forename: Horacio F
authors.initials: HF
authors.lastname: Cantiello
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002614:Chelating Agents; D006801:Humans; D017136:Ion Transport; D007700:Kinetics; D017434:Protein Structure, Tertiary; D050396:TRPP Cation Channels / Q000378:metabolism*; D014327:Trophoblasts / Q000378:metabolism*
chemical_list: D002118:Calcium; D002614:Chelating Agents; D050396:TRPP Cation Channels