title: Ca2+ and cAMP-activated Cl- conductances mediate Cl- secretion in a mouse renal inner medullary collecting duct cell line.
abstract: 1. The nature of Cl- conductance(s) participating in transepithelial anion secretion by renal inner medullary collecting duct (IMCD, mIMCD-K2 cell line) was investigated. 2. Extracellular ATP (100 microM) stimulated a transient increase in both whole-cell Cl- conductance and intracellular free Ca2+. In contrast, ionomycin (10-100 nM) caused a sustained increase in whole-cell Cl- conductance. Pre-loading cells with the Ca2+ buffer BAPTA abolished the ATP-dependent responses and delayed the onset of the increase observed with ionomycin. 3. The Ca2+-activated whole-cell Cl- current stimulated by ATP (peak) and ionomycin (maximal) displayed (i) a linear steady-state current-voltage relationship and (ii) time and voltage dependence with slow activation at +80 mV and slow inactivation at -80 mV. In BAPTA-loaded cells, ionomycin-elicited whole-cell currents exhibited pronounced outward rectification with time-dependent activation/inactivation. 4. Ca2+-activated and forskolin-activated Cl- conductances co-exist since ATP activation of whole-cell current occurred during a maximal stimulation by forskolin in single cell recordings. 5. In IMCD epithelial layers, ATP and ionomycin stimulated an inward short circuit current (Isc) dependent upon basal medium Na+ and Cl-/HCO3- but independent of the presence of apical bathing medium Na+ and Cl-/HCO3-. This was identical to forskolin stimulation and consistent with transepithelial anion secretion. 6. PCR amplification of reverse-transcribed mRNA using gene-specific primers demonstrated expression of both cystic fibrosis transmembrane conductance regulator (CFTR) mRNA and Ca2+-activated Cl- channel (mCLCA1) mRNA in mIMCD-K2 cells. 7. Ca2+ and forskolin-activated Cl- conductances participate in anion secretion by IMCD.
authors.affiliation: Department of Physiological Sciences, Medical School, Framlington Place, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
authors.forename: S H
authors.initials: SH
authors.lastname: Boese
authors.forename: M
authors.initials: M
authors.lastname: Glanville
authors.forename: O
authors.initials: O
authors.lastname: Aziz
authors.forename: M A
authors.initials: MA
authors.lastname: Gray
authors.forename: N L
authors.initials: NL
authors.lastname: Simmons
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D018118:Chloride Channels / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000096:biosynthesis / Q000235:genetics; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D007202:Indicators and Reagents / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D018118:Chloride Channels; D002712:Chlorides; C116464:Clca3a1 protein, mouse; D007202:Indicators and Reagents; D007476:Ionophores; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D004533:Egtazic Acid; D015759:Ionomycin; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium