title: Human ClCa1 modulates anionic conduction of calcium-dependent chloride currents.
abstract: Proteins of the CLCA gene family including the human ClCa1 (hClCa1) have been suggested to constitute a new family of chloride channels mediating Ca(2+)-dependent Cl- currents. The present study examines the relationship between the hClCa1 protein and Ca(2+)-dependent Cl- currents using heterologous expression of hClCa1 in HEK293 and NCIH522 cell lines and whole cell recordings. By contrast to previous reports claiming the absence of Cl- currents in HEK293 cells, we find that HEK293 and NCIH522 cell lines express constitutive Ca(2+)-dependent Cl- currents and show that hClCa1 increases the amplitude of Ca(2+)-dependent Cl- currents in those cells. We further show that hClCa1 does not modify the permeability sequence but increases the Cl- conductance while decreasing the G(SCN-)/G(Cl-) conductance ratio from approximately 2-3 to approximately 1. We use an Eyring rate theory (two barriers, one site channel) model and show that the effect of hClCa1 on the anionic channel can be simulated by its action on lowering the first and the second energy barriers. We conclude that hClCa1 does not form Ca(2+)-dependent Cl- channels per se or enhance the trafficking/insertion of constitutive channels in the HEK293 and NCIH522 expression systems. Rather, hClCa1 elevates the single channel conductance of endogenous Ca(2+)-dependent Cl- channels by lowering the energy barriers for ion translocation through the pore.
authors.affiliation: Leicester University, Department of Cell Physiology and Pharmacology, Medical Sciences Building, PO Box 138, University Road, Leicester LE1 9HN, UK. mh86@le.ac.uk
authors.forename: Martine
authors.initials: M
authors.lastname: Hamann
authors.forename: Adele
authors.initials: A
authors.lastname: Gibson
authors.forename: Noel
authors.initials: N
authors.lastname: Davies
authors.forename: Amanda
authors.initials: A
authors.lastname: Jowett
authors.forename: Jean Philippe
authors.initials: JP
authors.lastname: Walhin
authors.forename: Leanne
authors.initials: L
authors.lastname: Partington
authors.forename: Karen
authors.initials: K
authors.lastname: Affleck
authors.forename: Derek
authors.initials: D
authors.lastname: Trezise
authors.forename: Martin
authors.initials: M
authors.lastname: Main
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D004558:Electric Stimulation; D055724:Electrophysiological Phenomena / Q000187:drug effects / Q000502:physiology*; D015870:Gene Expression / Q000235:genetics; D005942:Gluconates / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D008958:Models, Molecular; D009544:Niflumic Acid / Q000494:pharmacology; D010539:Permeability; D013816:Thermodynamics; D013861:Thiocyanates / Q000494:pharmacology; D014162:Transfection
chemical_list: C492109:CLCA1 protein, human; D018118:Chloride Channels; D002712:Chlorides; D005942:Gluconates; D013861:Thiocyanates; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D009544:Niflumic Acid; C031760:thiocyanate; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C030691:gluconic acid; D002118:Calcium