E Peles — Page 3 | PubMed Health

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Myelinating Schwann cells determine the internodal localization of Kv1.1, Kv1.2, Kvbeta2, 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 beta2 subunit are localized to the juxtaparanode. Throughout the internodal region, a strand of Caspr staining is flanked by a double strand of Kv1.1/Kv1.2/Kvbeta2 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 not disrupted in mice with null mutations of the myelin associated glycoprotein, connexin32, or Kv1.1 genes. At all of these locations, Caspr and Kv1.1/Kv1.2/Kvbeta2 define distinct but interrelated domains of the axonal membrane that appear to be organized by the myelin sheath.

Animals↗

PubMedDate not supplied

K+ channel distribution and clustering in developing and hypomyelinated axons of the optic nerve.

The localization of Shaker-type K(+) channels in specialized domains of myelinated central nervous system axons was studied during development of the optic nerve. In adult rats Kv1.1, Kv1.2, Kv1.6, and the cytoplasmic beta-subunit Kvbeta2 were colocalized in juxtaparanodal zones. During development, clustering of K(+) channels lagged behind that for nodal Na(+) channels by about 5 days. In contrast to the PNS, K(+) channels were initially expressed fully segregated from nodes and paranodes, the latter identified by immunofluorescence of Caspr, a component of axoglial junctions. Clusters of K(+) channels were first detected at postnatal day 14 (P14) at a limited number of sites. Expression increased until all juxtaparanodes had immunoreactivity by P40. Developmental studies in hypomyelinating Shiverer mice revealed dramatically disrupted axoglial junctions, aberrant Na(+) channel clusters, and little or no detectable clustering of K(+) channels at all ages. These results suggest that in the optic nerve, compact myelin and normal axoglial junctions are essential for proper K(+) channel clustering and localization.

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