title: Time-dependent apical membrane K+ and Na+ selectivity in cultured kidney cells.
abstract: Intracellular microelectrodes were used to study apical membrane selectivity to Na+ and K+ of cultured toad kidney cells (A6) grown on permeable supports. Membrane selectivity was tested by responses of apical membrane potential to replacement of Na+ by K+ or tetraethylammonium and by addition of amiloride to perfusion solutions. The A6 epithelia fell into two groups: those with K+-selective apical membranes, lack of amiloride sensitivity, and near-zero transepithelial potential (group I); and those with Na+-selective apical membranes and a serosa-positive, amiloride-sensitive transepithelial potential (Vm----s; group II). The transition from group I to group II behavior appeared definitive and time dependent, occurring approximately 10 days after plating onto filters. Transepithelial measurements under sterile conditions showed that overnight incubation with aldosterone (10(-7) M), after development of tight junctions (transepithelial resistance elevated) but before development of significant Vm----s, induced the switch from group I to group II behavior. Apical addition of Ba2+, a known blocker of K+ channels, unexpectedly reduced transepithelial resistance (Rm----s) in group I and group II A6, suggesting that it not only blocked K+ channels (when they are present) but may also open a parallel conductive pathway. In summary, after approximately 10 days in culture, apical membranes of A6 epithelia undergo a switch from K+ to Na+ selectivity, overnight incubation with aldosterone can trigger this change, and finally, Ba2+ may open a paracellular conductive pathway.
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism / Q000648:ultrastructure; D007668:Kidney / Q000378:metabolism* / Q000648:ultrastructure; D008839:Microelectrodes; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
chemical_list: D012964:Sodium; D011188:Potassium