AJP - Cell Physiology, Vol 236, Issue 5 225-C232, Copyright © 1979 by American Physiological Society
Correlated release of acetylcholine and protein from the neuromuscular junction
J. R. Musick
Transmitter release at adrenergic synapses is accompanied by release of
chromogranin proteins, which are contained in synaptic vesicles. To
determine if a similar phenomenon occurs at the neuromuscular junction,
correlated release of acetylcholine (ACh) and protein was investigated
using in vitro neuromuscular preparations (phrenic nerve-diaphragm muscle
of the rat and mouse, sciatic nerve-sartorius muscle of Rana pipiens and R.
catesbeiana). Nerve stimulation of curare-paralyzed preparations increased
the rate of efflux of Lowry-reactive material relative to control values.
Stimulus-specific responses outlasted the period of neural stimulation.
Stimulus-induced release of Lowry-reactive material was correlated with ACh
release since it was Ca2+ dependent and Mg2+ antagonized. Conditions that
potentiate spontaneous ACh release also significantly increased the rate of
efflux of Lowry-reactive material. Most of the Lowry-reactive material
released with ACh is not a secretory product of synaptic vesicles because
the amount released exceeds the contents of synaptic vesicles that undergo
exocytosis. It is concluded that ACh release from the neuromuscular
junction is accompanied by release of proteinaceous material that is not
entirely derived from synaptic vesicles.
