title: Chloride currents in acutely isolated Xenopus retinal pigment epithelial cells.
abstract: The retinal pigment epithelium (RPE) regulates the ionic composition of the fluid surrounding the photoreceptors by transport mechanisms that utilize Cl- channels. Cl- currents in RPE cells, however, remain incompletely characterized. The purpose of this study was to identify the Cl- currents in acutely isolated Xenopus RPE cells using whole-cell patch clamp. We describe three different Cl- currents. (1) An inwardly rectifying Cl- current, ICl,ir, activates slowly with hyperpolarization (tauact = ~1 s at -80 mV, V1/2= -94 +/- 3 mV), is blocked by Zn2+ (IC50 =185 microM), is stimulated by acid (ICl,ir is 5 times larger at pH 6 than pH 8), and is blocked by DIDS in a voltage-dependent manner. ICl,ir closely resembles cloned ClC-2currents. (2) An outwardly rectifying Cl- current, ICl,Ca, is stimulated by elevated cytosolic free [Ca2+]. With 1 microM free [Ca2+]i in the patch pipette, ICl,Ca activates slowly with depolarization (tauact =325 ms at 100 mV) and deactivates upon hyperpolarization. ICl,Ca is not blocked by 1 mM Zn2+ or 10 microM Gd3+ but is blocked by DIDS. High extracellular [Ca2+] (10 mM) also activates ICl,Ca. (3) A non-rectifying current is activated by elevation of cytoplasmic cAMP with forskolin and IBMX. In addition to these three Cl- currents, Xenopus RPE cells exhibit a non-selective background current (Ibkg) which has a linear I-V relationship and is voltage insensitive. This current is blocked by Zn2+ (IC50 of 5.3 microM) or 10 microM Gd3+. This description provides new insights into the physiology of Cl- channels involved in salt and fluid transport by the retinal pigment epithelium.
authors.affiliation: Department of Cell Biology, Whitehead Biomedical Research Building 535, 615 Michael Street, Emory University School of Medicine, Atlanta, GA 30322-3030, USA. criss@cellbio.emory.edu
authors.forename: H Criss
authors.initials: HC
authors.lastname: Hartzell
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Qu
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism; D000242:Cyclic AMP / Q000502:physiology; D004553:Electric Conductivity; D045604:Extracellular Fluid / Q000378:metabolism; D005682:Gadolinium / Q000494:pharmacology; D007700:Kinetics; D018408:Patch-Clamp Techniques; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000502:physiology; D014982:Xenopus laevis; D015032:Zinc / Q000494:pharmacology
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D020033:Protein Isoforms; D005682:Gadolinium; D000242:Cyclic AMP; D015032:Zinc; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium