title: CFTR-regulated chloride transport at the ocular surface in living mice measured by potential differences.
abstract: OBJECTIVE
  To define the role of the cystic fibrosis transmembrane conductance regulator (CFTR) in Cl(-) secretion at the mouse ocular surface in vivo.
  
  
  METHODS
  Open-circuit potential differences (PDs) across the fluid-bathed ocular surface were measured in anesthetized wild-type and cystic fibrosis (CF) mice in response to Cl(-) ion substitution and transport agonists and inhibitors.
  
  
  RESULTS
  Basal ocular surface PD was -23 +/- 1 mV (SE; 20 wild-type mice), depolarizing to -16 +/- 2 mV after amiloride, then hyperpolarizing to -34 +/- 3 mV after low Cl(-). CFTR activation by forskolin or a selective activator caused further sustained hyperpolarization to -50 to -60 mV. UTP produced a comparable but transient hyperpolarization. The CFTR inhibitors CFTR(inh)-172 and GlyH-101 largely reversed agonist- but not low Cl(-)-induced hyperpolarizations. PD in CF mice hyperpolarized by 2.1 mV after low Cl(-) and was insensitive to CFTR activators or inhibitors.
  
  
  CONCLUSIONS
  CFTR provides a major pathway for mouse ocular surface Cl(-) secretion, suggesting the application of CFTR activators as therapy for dry eye. Amiloride-sensitive Na(+) transporters facilitate Na(+) absorption. PD measurements provide a robust and reproducible means of assessing ocular surface ion transporting mechanisms.
authors.affiliation: Department of Medicine, Cardiovascular Research Institute, University of California San Francisco, San Francisco, California, USA.
authors.forename: Marc H
authors.initials: MH
authors.lastname: Levin
authors.forename: A S
authors.initials: AS
authors.lastname: Verkman
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D003228:Conjunctiva / Q000378:metabolism*; D003315:Cornea / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000037:antagonists & inhibitors / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism; D017136:Ion Transport; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D018181:Mice, Inbred CFTR; D008817:Mice, Mutant Strains; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
chemical_list: C482900:3-((3-trifluoromethyl)phenyl)-5-((3-carboxyphenyl)methylene)-2-thioxo-4-thiazolidinone; D001565:Benzoates; D002712:Chlorides; D013844:Thiazoles; D053778:Thiazolidines; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D000584:Amiloride