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.

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PubMedDate not supplied

Analysis of potassium channel functions in mammalian axons by gene knockouts.

Mammalian axons express a rich repertoire of various K channel subtypes whose distribution is profoundly affected by myelination. In the past two decades, functional analysis of axonal K channels has been approached primarily through pharmacology. Recently, gene knockout techniques have been used to specifically delete a particular K channel subtype from axons. This is significant since the bulk of K channels in a myelinated nerve are covered by the myelin, making functional analysis of specific K channel subtypes by traditional means difficult. This review summarizes the first mutational analysis of this sort performed on an axonal fast K channel termed Kv1.1. This K channel is concealed by the myelin loops in the paranodes of all major myelinated fiber tracts, and exhibits highly heterogeneous distribution even in certain non-myelinated CNS axons. Physiological analysis of Kv1.1 null mutants suggest novel functions for this axonal K channel subtype, including modulation of conduction failures at branch points and stabilization of transition zones in myelinated nerves.

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PubMedDate not supplied

Neuronal-type Na+ and K+ channels in rabbit cultured Schwann cells.

Nerve axons in the central and peripheral nervous system are normally surrounded by satellite cells. These cells, known as Schwann cells in the peripheral nervous system, interact with axons to form a myelin sheath, so allowing nerve impulses to proceed at high speed. Schwann cells are thought to differ from neurones in their membrane properties in one important aspect: they lack excitability. Using the patch-clamp technique we have now measured directly the ionic currents across the membrane of single Schwann cells cultured from newborn rabbits. Surprisingly, we found that these Schwann cells possess voltage-gated sodium and potassium channels that are similar to those present in neuronal membranes.

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