AJP - Renal Physiology, Vol 245, Issue 6 660-F669, Copyright © 1983 by American Physiological Society
Mode of inhibition of active chloride transport in the frog cornea by furosemide
R. Patarca, O. A. Candia and P. S. Reinach
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.
