Expression of potassium channels in epithelial cells depends on calcium-activated cell-cell contacts

Abstract

Harvesting MDCK cells with trypsin-EDTA reduces potassium currents (I _K) to a mere 10%, presumably by hydrolysis of K⁺ channels, but replating at confluence restores them in 12–18 hr, through a process that requires transcription, translation and exocytic fusion of intracellular membrane vesicles to the plasma membrane (Ponce & Cereijido, 1991; Ponce et al., 1991a). In the present work we find that this restoration of I _K also requires cell-cell contacts and the presence of 1.8 mm Ca²⁺. The role of extracellular Ca²⁺ may be substituted by 2.0 μm TRH, 10 nm PMA or 200 μg/ml DiC8, drags that stimulate the system of phospholipase C (PLC) and protein kinase C (PKC). Conversely, the recovery of I _K triggered by Ca-dependent contacts can be blocked by 110 μm neomycin, 2.0 μm H7, and 250 nm staurosporine, inhibitors of PLC and PKC. These results suggest that the expression of new K⁺ channels depends on Ca²⁺-activated contacts with neighboring cells and that the information is conveyed through PLC and PKC, a process in keeping with changes in its enzymatic activity and cellular distribution of PKC. Plasma membrane is also reduced and restored upon harvesting and replating, and depends on Ca²⁺-activated contracts. However, the effects of the chemicals tested on I _K differ from the ones they elicit on the recovery of plasma membrane, suggesting that cells can independently regulate their population of K⁺ channels and the surface of their membrane.