Extracellular detection of K+ release during migration of transformed Madin-Darby canine kidney cells.
Madin Darby canine kidney cells transformed by alkaline stress (MDCK-F cells) constitutively migrate at a rate of about 1 microm.min-1. Migration depends on the intermittent activity of a Ca2+-stimulated, 53-pS K+ channel (KCa channel) that is inhibitable by charybdotoxin. In the present study we examined whether this intermittent KCa channel activity results in a significant K+ loss across the plasma membrane. K+ efflux from MDCK-F cells should result in a transient increase of extracellular K+ ([K+]e) in the close vicinity of a migrating cell. However, due to the rapid diffusion of K+ ions into the virtually infinite extracellular space, such a transient increase in [K+]e was too small to be detected by conventional K+-selective electrodes. Therefore, we developed a "shielded ion-sensitive microelectrode" (SIM) that limited diffusion to a small compartment, formed by a shielding pipette which surrounded the tip of the K+-sensitive microelectrode. The SIM improved the signal to noise ratio by a factor of at least three, thus transient increases of [K+]e in the vicinity of MDCK-F cells became detectable. They occurred at a rate of 1.3 min-1. The cell releases 40 fmol K+ during each burst of intermittent KCa channel activity, which corresponds to about 15% of the total cellular K+ content. Since transmembrane K+ loss must be accompanied by anion loss and therefore leads to a decrease of cell volume, these findings support the hypothesis that intermittent volume changes are a prerequisite for the migration of MDCK-F cells.
Danker
T
T
Physiologisches Institut, Röntgenring 9, D-97070 Würzburg, Germany.
Gassner
B
B
Oberleithner
H
H
Schwab
A
A
D000818:Animals; D002461:Cell Line, Transformed; D002465:Cell Movement; D004285:Dogs; D004867:Equipment Design; D005110:Extracellular Space / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D008839:Microelectrodes; D008954:Models, Biological; D010812:Physical Stimulation; D011188:Potassium / Q000378:metabolism*
D011188:Potassium