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 coassembl y is random and inevitable or whether highly homologous channels can b e segregated and targeted independently within a given cell has not be en determined, In this study, we address these questions by characteri zing and localizing voltage-dependent K+ channels in Schwann cells, Tr anscripts 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 dis tributions, Kv1.5 is localized on the Schwann cell membrane at the nod es of Ranvier and in bands that run along the outer surface of the mye lin, It is also seen intracellularly in the vicinity of the nucleus, S chwann cell staining for Kv1.1, on the other hand, was seen only in pe rinuclear, 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, Kv 1.1 was highly concentrated in the axonal membrane at juxtaparanodal r egions. The distributions of these K+ channels in myelinated nerve hig hlight the elaborate molecular specializations of these membranes.