Voltage and Ca2+-activated K+ channel in cultured epithelial cells (MDCK)

Patch-clamp techniques were used to study a K channel in the cell membrane of MDCK cells. This cell line derives from the kidney of a normal dog, presumably from the distal nephron, a region involved in potassium secretion. The cells were cultured in confluent monolayers and approached from the apical side. The K channel we describe is Ca2+ and voltage activated, has a conductance of 221 +/- 7 pS, and can be inhibited by 10 mM tetraethylammonium and by 1 mM quinidine, but not by 4-aminopyridine, nor by 1 mM Ba2+ added to the outer side. Using the whole-cell configuration, we find that most of the cationic conductance of the membrane is constituted by a K-specific one (maximum K conductance 32.1 +/- 3.9 nS vs. a leak conductance of 1.01 +/- 0.17 nS). Comparisons of the maximum K conductance with that of a single K channel indicates that an MDCK cell has an average of 145 such channels. The membrane capacity is 24.5 +/- 1.4 pF.