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Journal of Neuroscience, Vol 16, 2421-2429, Copyright © 1996 by Society for Neuroscience
Inwardly rectifying K+ channels that may participate in K+ buffering are localized in microvilli of Schwann cells
H Mi, TJ Deerinck, M Jones, MH Ellisman and TL Schwarz
Department of Molecular and Cellular Physiology, Beckman Center, Stanford University Medical Center, California 94305, USA.
The presence of K+ channels on the Schwann cell plasma membrane suggests
that Schwann cells may participate actively during action potential
propagation in the peripheral nervous system. One such role for Schwann
cells may be to maintain a constant extracellular concentration of K+ in
the face of K+ efflux from a repolarizing axon. This buffering is likely to
involve the influx of K+ through inward rectifying K+ channels. The
molecular cloning of these genes allowed us to examine their expression and
localization in Schwann cells in detail. In this study, we demonstrate the
expression of two inward rectifying K+ channels, IRK1 and IRK3, in adult
rat sciatic nerve. Immunocytochemistry using a polyclonal antibody against
these proteins showed that the channels were highly localized at nodes in
sciatic nerve. By immunoelectron microscopy, the nodal staining was shown
to be concentrated in the microvilli of Schwann cells (also called nodal
processes). The large surface area of the microvilli and their presence in
the nodal space suggest involvement with ionic buffering. Thus, IRK1 and
IRK3 are well suited to K+ buffering by virtue of both their biophysical
properties and their localization. The restricted distribution of the
inward rectifying K+ channels also provides an example of the highly
regulated localization of ion channels to their specialized membrane
domains. In the Schwann cell, where the nodal processes are a minute
fraction of the total cell membrane, a potent mechanism must be present to
concentrate the channels in this structure.
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