POTASSIUM PERMEABLE CHANNELS IN PRIMARY CULTURES OF RABBIT CORTICAL COLLECTING TUBULE

Rabbit cortical collecting tubule (RCCT) primary cultures, were grown on permeable. collagen supports with 1.5-mu-M aldosterone. Single K+ permeable channels in principal cell apical membranes were examined. At applied patch pipette potential (V(app)) from -60 to +60 mV (cell interior with respect to pipette interior). outward currents (cell to pipette) with a unitary conductance of 8 to 10 pS were seen in cell-attached (N = 31) and excised inside-out (N = 15) patches. At resting membrane potential (V(app) = 0 mV), mean open probability (P(o) = 0.85 +/- 0.16) decreased by 50% with 0.75 mM luminal BaCl2 exposure. In cell-attached patches, a second type of outward current was seen only at extreme depolarization, V(app) > +80 mV (N = 9). Usually in the closed state (P(o) < 0.0005) at no applied potential, P(o) for this 150 pS channel increased dramatically with depolarization and/or raising cytoplasmic Ca2+. With a calculated K+ equilibrium potential of -84 mV, excised patch reversal potentials were < -50 mV for both the above channel types, indicating high selectivity for K+ over Na+. In cultures grown without aldosterone low conductance K+ channels were rarely observed, while mineralocorticoid status did not appear to affect high conductance K+ channel frequency. Finally, a 30 pS cation channel was found to be nonselective for K+ over Na+, and insensitive to voltage, intracellular Ca2+ or luminal Ba2+. We conclude that: 1) Principal cell apical membranes from aldosterone-stimulated. RCCT primary cultures contain (a) low conductance. Ba2+-inhibitable and (b) high conductance, Ca2+/voltage-dependent K+ channels: and c) nonselective cation channels. 2) The low conductance K+ channel may play an important physiologic role in native RCCT mineralocorticoid-controlled K+ secretion, while the latter two channels' functions are unknown, although similar channels have been suggested to play a role in cell volume regulation.