CLCA protein and chloride transport in canine retinal pigment epithelium.
Problems in ion and fluid transfer across the retinal pigment epithelium (RPE) are a probable cause of inappropriate accumulations of fluid between the photoreceptors of the retina and the RPE. The activities of Cl- transporters involved in basal fluid transfer across the RPE have been compared to determine whether Ca2+- or cAMP-dependent channels may be responsible for basal housekeeping levels of secretory activity in this tissue. The role of a candidate Ca2+-dependent CLCA protein in the basal RPE transport of Cl- has been investigated. Low concentrations of the Cl- conductance inhibitors glibenclamide and 5-nitro-2-(3-phenylpropylamino)benzoate reduced the short-circuit current in dog RPE preparations mounted in Ussing chambers and decreased the Ca2+-dependent Cl- efflux from fibroblasts expressing the pCLCA1 Cl- conductance regulator. However, these same agents did not inhibit the rate of Cl- release from cultured fibroblasts expressing the cystic fibrosis transmembrane regulator (CFTR) conductive Cl- channel. Addition of ionomycin to primary cultures of canine RPE cells or to fibroblasts expressing the pCLCA1 channel regulator increased the rate of release of Cl- from both types of cultured cells. However, the presence of pCLCA1 also increased cAMP-dependent Cl- release from fibroblasts expressing CFTR. We conclude that Ca2+-dependent Cl- transport may be more important than cAMP-dependent Cl- transport for normal fluid secretion across the RPE. Furthermore, CLCA proteins expressed in the RPE appear to regulate the activity of other Cl- transporters, rather than functioning as primary ion transport proteins.
Loewen
Matthew E
ME
Department of Veterinary Biomedical Sciences, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5B4.
Smith
Nicola K
NK
Hamilton
Don L
DL
Grahn
Bruce H
BH
Forsyth
George W
GW
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002712:Chlorides / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004285:Dogs; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013552:Swine
C492109:CLCA1 protein, human; D018118:Chloride Channels; D002712:Chlorides