Journal of Neuroscience, Vol 3, 1414-1421, Copyright © 1983 by Society for Neuroscience
Muscle activity and the loss of electrical coupling between striated muscle cells in Xenopus embryos
DL Armstrong, L Turin and AE Warner
The gap junctions between embryonic striated muscle cells are lost during
development. The time course of their elimination has been examined with
electrophysiological techniques in myotomes of Xenopus laevis embryos. Gap
junctions were detected by the passage of electronic current or the
fluorescent dye, Lucifer Yellow, from one muscle cell to another. These
tracers only spread to neighboring cells when injected intracellularly. All
the muscle cells are electrically coupled at stage 24 when neuromuscular
transmission begins, but normally many cells become uncoupled during the
next 48 hr. In contrast, the muscle cells remain electrically coupled if
neuromuscular transmission is blocked during that period with tricaine or
alpha- bungarotoxin. When muscle activity recovers, the loss of coupling
resumes. Once the coupling has disappeared, neuromuscular blockade does not
restore it. Muscle contraction is blocked during development in a mutant of
Xenopus, even though the muscle cells remain electrically excitable. After
stage 32 in these immobile embryos, the muscle cells are stimulated
repeatedly by regular bursts of neural activity. Although they never
contract, the mutant muscle cells become uncoupled at the same time as the
muscle cells in normal embryos. The results suggest that some consequence
of repeated cholinergic activation, other than contraction, stimulates the
loss of gap junctions between striated muscle cells during development. The
elimination of gap junctions may be required for neural control of
subsequent muscle differentiation.
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