Ionic conductances of cultured principal cell epithelium of renal collecting duct

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Abstract
The ionic conductive properties were studied of epithelia of collecting duct principal cells which had been grown in primary tissue culture from renal cortex/capsule explants. When pretreated with aldosterone (10−6 mol/l) and bathed on either surface with isotonic HCO 3 − -free Ringer's solution, the transepithelial voltage,V te, varied between −21 and −72 mV (apical surface negative) while the transepithelial resistance,R te, ranged from 0.4 to 1.5 kΩcm2. By 10:1 step-changes in Na+ concentration the apical cell membrane was shown to have a high conductivity for sodium, inhibitable by amiloride, 10−6 mol/l. However, contrary to observations in natural collecting duct under control conditions, amiloride never reversed the polarity ofV te even at 10−4 mol/l. Both the apical and the basolateral cell membranes were conductive for potassium and both conductivities were inhibitable by Ba2+ (5 mmol/l). 10:1 reduction of apical Cl− concentration strongly hyperpolarizedV te with a monophasic time course suggesting the presence of a paracellular shunt conductance for Cl−. In addition there may be a small Cl− conductance present in the apical cell membrane since apical application of the chloride channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPAB) at 10−7 mol/l produced a minute but significant hyperpolarization. On the other hand, 10:1 reduction of basolateral Cl− concentration caused a biphasic change inV te (initial depolarization, followed by repolarization) which indicates the presence of a large Cl− conductance in the basolateral cell membrane. The latter was not inhibitable by 10−7 mol/l NPPAB. Higher concentrations of this and of an other Cl− channel blocker produced non-specific effects. In conclusion, our studies of a pure principal cell epithelium confirm findings described for the intact cortical collecting duct and add new information concerning chloride conductivity and related blocking agents.