Myelinating Schwann cells determine the internodal localization of Kv1.1, Kv1.2, Kv beta 2, and Caspr

We examined the localization of Caspr and the K+ channels Kv1.1 and Kv1.2, all of which are intrinsic membrane proteins of myelinated axons in the PNS . Caspr is localized to the paranode; Kv1.1, Kv1.2 and their beta 2 subunit are localized to the juxtaparanode. Throughout the internodal region, a st rand of Caspr staining is flanked by a double strand of Kv1.1/Kv1.2/Kv beta 2 staining. This tripartite strand apposes the inner mesaxon of the myelin sheath, and forms a circumferential ring that apposes the innermost aspect of Schmidt-Lanterman incisures. The localization of Caspr and Kv1.2 are no t disrupted in mice with null mutations of the myelin associated glycoprote in, connexin32, or Kv1.1 genes. At all of these locations, Caspr and Kv1.1/ Kv1.2/Kv beta 2 define distinct but interrelated domains of the axonal memb rane that appear to be organized by the myelin sheath.