Mode of inhibition of active chloride transport in the frog cornea by furosemide.
The mechanism of inhibition of active Cl- secretion by 1 mM furosemide and 0.1 mM bumetanide was characterized in the isolated frog corneal epithelium. Transepithelial and transmembrane cell electrical parameters as well as transmembrane Cl- electrochemical potential difference were measured with conventional glass microelectrodes and Cl- selective microelectrodes. Furosemide caused the potential difference across the apical membrane to hyperpolarize by 20 mV while the transepithelial potential difference declined by 13 mV. The apical-to-basolateral membrane resistance ratio increased 3-4 times after furosemide or bumetanide addition. Preincubation with furosemide prevented a 30-mV depolarization of the apical membrane potential difference normally observed when Cl- was removed from the tear side bathing solution. In control conditions, intracellular Cl- activity was above equilibrium. Bumetanide further increased the Cl- electrochemical gradient between the cell compartment and the bathing solutions even though intracellular Cl- activity fell from 18 to 12 mM. In contrast, perfusion with Cl- -free Ringer in the stromal side bathing solution decreased the Cl- electrochemical gradient across the apical membrane to zero, indicating an equilibrium distribution. Adenosine, which selectively increases Cl- permeability of the apical membrane, also decreased the Cl- electrochemical gradient across the apical membrane. These results suggest that the diuretics inhibit active Cl- transport primarily by decreasing the Cl- permeability of the apical membrane.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D003315:Cornea / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D004848:Epithelium / Q000502:physiology; D005665:Furosemide / Q000494:pharmacology*; D007700:Kinetics; D008839:Microelectrodes; D008954:Models, Biological; D011892:Rana catesbeiana
D002712:Chlorides; D002034:Bumetanide; D005665:Furosemide