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 microM aldosterone. Single K+ permeable channels in principal cell apical membranes were examined. At applied patch pipette potential (Vapp) 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 (Vapp = 0 mV), mean open probability (Po = 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, Vapp greater than +80 mV (N = 9). Usually in the closed state (Po less than 0.0005) at no applied potential, Po 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 less than -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, Ba(2+)-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.
Ling
B N
BN
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia.
Hinton
C F
CF
Eaton
D C
DC
D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D017609:Barium Compounds; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002712:Chlorides; D015640:Ion Channel Gating / Q000187:drug effects; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009924:Organ Culture Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D011817:Rabbits
D017609:Barium Compounds; D015220:Calcium Channels; D002712:Chlorides; D015221:Potassium Channels; C024986:barium chloride; D001464:Barium; D000450:Aldosterone; D011188:Potassium; D002118:Calcium