Differential distribution of closely related potassium channels in rat Schwann cells.

Closely related K+ channels can coassemble to form heteromultimers in expression systems, as well as in vivo. Whether in vivo this coassembly is random and inevitable or whether highly homologous channels can be segregated and targeted independently within a given cell has not been determined. In this study, we address these questions by characterizing and localizing voltage-dependent K+ channels in Schwann cells. Transcripts for three closely related members of the Shaker-like family of K+ channels are found in adult rat sciatic nerve: Kv1.1, Kv1.2, and Kv1.5. We have examined two of these and observed that both Kv1.1 and Kv1.5 proteins are expressed in Schwann cells but differ in their distributions. Kv1.5 is localized on the Schwann cell membrane at the nodes of Ranvier and in bands that run along the outer surface of the myelin. It is also seen intracellularly in the vicinity of the nucleus. Schwann cell staining for Kv1.1, on the other hand, was seen only in perinuclear, intracellular compartments. These results provide evidence that closely related channels from the same family need not coassemble and can be localized differentially in the same cell. In addition, Kv1.1 was highly concentrated in the axonal membrane at juxtaparanodal regions. The distributions of these K+ channels in myelinated nerve highlight the elaborate molecular specializations of these membranes.