EXTRACELLULAR DETECTION OF K-DARBY CANINE KIDNEY-CELLS( RELEASE DURING MIGRATION OF TRANSFORMED MADIN)

Madin Darby canine kidney cells transformed by alkaline stress (MDCK-F cells) constitutively migrate at a rate of about 1 mu um . min(-1). M igration depends on the intermittent activity of a Ca2+-stimulated, 53 -pS K+ channel (K-Ca channel) that is inhibitable by charybdotoxin. In the present study we examined whether this intermittent K-Ca 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 e xtracellular K+ ([K+](e)) in the close vicinity of a migrating cell. H owever, due to the rapid diffusion of K+ ions into the virtually infin ite extracellular space, such a transient increase in [K+](e) was too small to be detected by conventional K+-Selective electrodes. Therefor e, we developed a ''shielded ion-sensitive microelectrode'' (SIM) that limited diffusion to a small compartment, formed by a shielding pipet te which surrounded the tip of the K+-sensitive microelectrode. The SI M improved the signal to noise ratio by a factor of at least three, th us transient increases of [K+](e) in the vicinity of MDCK-F cells beca me detectable. They occurred at a rate of 1.3 min(-1). The cell releas es 40 fmol K+ during each burst of intermittent K-Ca channel activity, which corresponds to about 15% of the total cellular K+ content. Sinc e transmembrane K+ loss must be accompanied by anion loss and therefor e leads to a decrease of cell volume, these findings support the hypot hesis that intermittent Volume changes are a prerequisite for the migr ation of MDCK-F cells.