Axon contact is associated with modified expression of functional potassium channels in mouse Schwann cells

In organotypic cultures of mouse dorsal root ganglia, Schwann cells were classed as isolated, that is to say without contact with neurites, or as attached to neurites. It was known that isolated Schwann cells in these cultures display two types of voltage-dependent K+ currents, a fast transient current and a delayed sustained current. In this study, we have investigated outward K+ currents on Schwann cells attached to neurites. These all had a sustained current whose amplitude, timecourse, outward rectification, cumulative inactivation and sensitivity to tetraethylammonium were similar to those of the sustained current on isolated cells. However, the attached cells differed from the isolated cells in that only 15% had a detectable transient current. We suggest three possible explanations for this result: (i) that only cells with reduced transient K+ current move to contact the axon; (ii) that functional expression of these channels is down-regulated by close association with the axon; or (iii) that the channels are lost by transfer to the axon.