Functions and distribution of voltage‐gated sodium and potassium channels in mammalian schwann cells

Abstract

Recent patch-clamp studies on freshly isolated mammalian Schwann cells suggest that voltage-gated sodium and potassium channels, first demonstrated in cells under culture conditions, are present in vivo. The expression of these channels, at least at the cell body region, appears to be dependent on the myelinogenic and proliferative states of the Schwann cell. Specifically, myelin elaboration is accompanied by a down regulation of functional potassium channel density at the cell body. One possibility to account for this is a progressive regionalization of ion channels on a Schwann cell during myelin formation. In adult myelinating Schwann cells, voltage-gated potassium channels appear to be localized at the paranodal region. Theoretical calculations have been made of activity-dependent potassium accumulations in various compartments of a mature myelinated nerve fibre; the largest potassium accumulation occurs not at the nodal gap but rather at the adjacent 2-4 microns length of periaxonal space at the paranodal junction. Schwann cell potassium channels at the paranode may contribute to ionic regulation during nerve activities.

K+Channel Expression and Cell Proliferation Are Regulated by Intracellular Sodium and Membrane Depolarization in Oligodendrocyte Progenitor Cells

“…Biii, Despite a 60% attenuation of current density, the transient current component possessed voltage-dependent activation properties (Ϫ6 Ϯ 1.3 mV, n ϭ 13) identical to that seen in control treated cells. (Orkand et al, 1966;Chiu, 1991) by providing a rapid and efficient removal of ions by taking up K ϩ . In agreement with this hypothesis, Wilson and Chiu (1990) demonstrated that inwardly rectifying K ϩ channels are concentrated in Schwann cell membranes in the vicinity of the nodes of Ranvier, an area associated with the extrusion of K ϩ into the extracellular environment after action potential activity.…”

Current status of experimental cell replacement approaches to spinal cord injury

“…After PNS injury, Schwann cells provide a growth-promoting environment for regenerating axons through secretion of neurotrophic factors 1 and extracellular matrix elements 22 and ultimately myelinate the axons. Several groups have studied transplantation of Schwann cells after SCI and have shown successful integration of these cells in the host tissue with some regeneration of sensory axons and myelination of these axons associated with modest improvement of hindlimb function.…”

Glial potassium channels activated by neuronal firing or intracellular cyclic AMP in Helix.

“…During the last decade, a corpus of data has accumulated demonstrating that glial cells possess a wide range of ion channels (reviews by Barres, Chun & Corey, 1990;Barres, 1991;Chiu, 1991;Ritchie, 1992;Sontheimer, 1992) and neurotransmitter receptors (Barres, 1991). This prompted the idea that messages might be exchanged between glial cells and neurones.…”