Ca2+-activated K+ channels in cultured medullary thick ascending limb cells.
The conductive properties of a clone of medullary thick ascending limb (MTAL) cells (GRB-MAL1) were assessed using conventional microelectrodes and the patch clamp technique. The apical cell membrane potential (Va) of MTAL cells was -46 +/- 3 mV. Addition of Ba2+ (1 mM) to the apical solution induced a 22 +/- 2 mV depolarization of Va, whereas furosemide hyperpolarized Va by -5 +/- 1 mV. In the cell-attached patch configuration, the most frequently occurring channel had a single channel conductance of 121 +/- 5 pS and carried outward current. In excised patches, current movement was down the electrochemical K+ gradient. Fluctuations were activated by depolarization of Va and by increasing Ca2+ concentration on the intracellular face. Micromolar amounts of Ba2+ on the intracellular face of the membrane inhibited channel activity. We conclude that cultures of MTAL cells GRB-MAL1 retain at least two of the properties of the mature phenotype, namely, an apical K+ conductance and a sensitivity to loop diuretics; the most frequently occurring channel in the apical cell membrane is a Ca2+-activated, maxi-K+ channel; and, finally Ca2+-activated K+ channels may play a role in generating the apical K+ conductance in cultured MTAL cells.
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D004553:Electric Conductivity; D005665:Furosemide / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007684:Kidney Tubules / Q000502:physiology*; D008138:Loop of Henle / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits
D007473:Ion Channels; D001464:Barium; D005665:Furosemide; D011188:Potassium; D002118:Calcium