title: Calbindin-D28K dynamically controls TRPV5-mediated Ca2+ transport.
abstract: In Ca(2+)-transporting epithelia, calbindin-D(28K) (CaBP(28K)) facilitates Ca(2+) diffusion from the luminal Ca(2+) entry side of the cell to the basolateral side, where Ca(2+) is extruded into the extracellular compartment. Simultaneously, CaBP(28K) provides protection against toxic high Ca(2+) levels by buffering the cytosolic Ca(2+) concentration ([Ca(2+)](i)) during high Ca(2+) influx. CaBP(28K) consistently colocalizes with the epithelial Ca(2+) channel TRPV5, which constitutes the apical entry step in renal Ca(2+)-transporting epithelial cells. Here, we demonstrate using protein-binding analysis, subcellular fractionation and evanescent-field microscopy that CaBP(28K) translocates towards the plasma membrane and directly associates with TRPV5 at a low [Ca(2+)](i). (45)Ca(2+) uptake measurements, electrophysiological recordings and transcellular Ca(2+) transport assays of lentivirus-infected primary rabbit connecting tubule/distal convolute tubule cells revealed that associated CaBP(28K) tightly buffers the flux of Ca(2+) entering the cell via TRPV5, facilitating high Ca(2+) transport rates by preventing channel inactivation. In summary, CaBP(28K) acts in Ca(2+)-transporting epithelia as a dynamic Ca(2+) buffer, regulating [Ca(2+)] in close vicinity to the TRPV5 pore by direct association with the channel.
authors.affiliation: Department of Physiology, Radboud University Nijmegen Medical Centre, The Netherlands.
authors.forename: Tim T
authors.initials: TT
authors.lastname: Lambers
authors.forename: Frank
authors.initials: F
authors.lastname: Mahieu
authors.forename: Elena
authors.initials: E
authors.lastname: Oancea
authors.forename: Louis
authors.initials: L
authors.lastname: Hoofd
authors.forename: Frank
authors.initials: F
authors.lastname: de Lange
authors.forename: Arjen R
authors.initials: AR
authors.lastname: Mensenkamp
authors.forename: Thomas
authors.initials: T
authors.lastname: Voets
authors.forename: Bernd
authors.initials: B
authors.lastname: Nilius
authors.forename: David E
authors.initials: DE
authors.lastname: Clapham
authors.forename: Joost G
authors.initials: JG
authors.lastname: Hoenderop
authors.forename: René J
authors.initials: RJ
authors.lastname: Bindels
mesh_terms: D000818:Animals; D064092:Calbindin 1; D064026:Calbindins; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D017136:Ion Transport; D007684:Kidney Tubules / Q000166:cytology / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000502:physiology*; D050916:TRPV Cation Channels / Q000502:physiology*; D019459:Urothelium / Q000166:cytology / Q000378:metabolism
chemical_list: C576498:CALB1 protein, human; D064092:Calbindin 1; D064026:Calbindins; D011994:Recombinant Proteins; D064030:S100 Calcium Binding Protein G; D050916:TRPV Cation Channels; D002118:Calcium