AJP - Renal Physiology, Vol 250, Issue 5 850-F859, Copyright © 1986 by American Physiological Society
Na+-K+ pump stoichiometry and basolateral membrane permeability of frog corneal epithelium
O. A. Candia and P. Cook
The Na+-K+ pump flux ratio and the Na+ and K+ permeability of the
basolateral membrane of the isolated frog corneal epithelium were studied
with the aid of microelectrodes by analyzing the effects of ouabain, Ba2+,
and amphotericin B. The experiments were done in Cl(-)-free solutions, a
situation that approximates that of static head. Ouabain produced a quick
depolarization of the potential difference across the basolateral membrane
(PDb) from -72 to -62 mV without a change in resistance. Ba2+ (3 mM)
rapidly lowered PDb from -74 to -57 mV and decreased the
apical-to-basolateral resistance ratio. The effects of ouabain and Ba2+
were additive. The Na+-K+ flux ratio at the pump was calculated to be 1.78,
substantially less than when the tissue is in a level flow condition,
suggesting a variable stoichiometry. The K+ and Na+ resistances of the
basolateral membrane were 15.7 and 5.5 k omega X cm2, respectively,
allowing K+ and Na+ currents that approximately matched those produced by
the Na+-K+ pump. The resistance of the basolateral membrane (4.0 k omega X
cm2) was double that reported in Cl(-)-rich solutions, suggesting that Cl-
contributes to the conductance of this membrane.
