Regulation of intracellular chloride in bullfrog choroid plexus.
Intracellular Cl- activity (AiCl) of the bullfrog choroidal epithelium has been studied using double-barreled Cl(-)-selective microelectrodes. In bicarbonate-buffered saline, the brush-border membrane potential (VVC) was -43 mV, and AiCl was 24 mM which was twice the predicted equilibrium activity. The uphill Cl- accumulation required the presence of external Na+ and was inhibited by furosemide added to the basolateral side. Removal of HCO3- from the bath solution slightly increased AiCl. On addition of 3-isobutyl-1-methylxanthine (IBMX), VVC depolarized, and AiCl approached the equilibrium activity. It is concluded that net Cl- secretion by the choroidal epithelium is mediated by a furosemide-sensitive, Na+-coupled Cl- uptake mechanism at the basolateral border and a Cl- conductive pathway at the brush border membrane. The results suggest that intracellular cAMP either increases the Cl- conductance of the epithelial membranes and/or inhibits the NaCl co-transport mechanism.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000502:physiology; D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism* / Q000502:physiology; D002831:Choroid Plexus / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004563:Electrochemistry; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D011892:Rana catesbeiana; D012964:Sodium / Q000502:physiology
D001639:Bicarbonates; D002712:Chlorides; D005665:Furosemide; D012964:Sodium; D015056:1-Methyl-3-isobutylxanthine