Journal of Neuroscience, Vol 10, 1615-1625, Copyright © 1990 by Society for Neuroscience
Potassium channel regulation in Schwann cells during early developmental myelinogenesis
GF Wilson and SY Chiu
Department of Neurophysiology, University of Wisconsin, Madison 53706.
The presence of neuronal-like, voltage-gated ion channels on glia has
raised questions concerning their physiological roles. Insights into glial
channel function can be gained by examining regulation of channel
expression during axoglial interactions. We examine the regulation of
Schwann cell potassium channels in developing sciatic nerves of newborn
rats when myelin is first laid down. During the initial postnatal week,
cell-attached patch-clamp recordings at soma of Schwann cells with visible
myelin revealed an inward rectifying potassium channel (KIR), to date
described only in CNS glia but not Schwann cells, as well as an outward
potassium channel (KO). Around the resting potential, the KO channel is
virtually closed, while the KIR channel appears maximally open. Compared
with the KO channel, the KIR channel is blocked by low concentrations of
Cs+ and exhibits higher sensitivity to 4- aminopyridine (4AP). Further, the
KIR channel appears similar to other mammalian inward rectifiers and
rectification depends, in part, on cytoplasmic Mg2+. Channel regulation
bears an interesting relation to early myelination: as the average number
of myelin lamellae increases from 6 to 21 from day 2 to day 8, currents
decrease by 80-90%. The reduction in KO current also parallels the known
decrease in proliferation of Schwann cells as they are being committed to
myelination, supporting the recently proposed notion of a functional link
between potassium channels and proliferation. The KIR channels, by virtue
of being open at the resting potential, may play a role in buffering
activity-dependent K+ accumulation during early myelin formation. The
subsequent reduction in somal channel density may parallel a diminished
need for K+ buffering as electrogenesis is restricted to nodal regions.
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