Journal of Neuroscience, Vol 6, 1545-1552, Copyright © 1986 by Society for Neuroscience
Neuropeptide routing in the bag cells: kinetic differences in the appearance of newly labeled peptides in transport and secretion
S Arch, A Linstedt, G Whitney, P Teal and T Smock
The bag cell neurons of Aplysia synthesize and secrete several peptides.
Some of these, in addition to the egg-laying hormone (ELH), are strongly
implicated in the various alterations of central neuronal activity that
accompany an electrical discharge of the bag cells. Thus, the secreted
peptides appear to play a variety of roles in the animal's physiology. We
have been interested in the intracellular mechanisms that precede peptide
secretion from the bag cells because of the evidence that most, if not all,
of these peptides are derived from a common precursor. Our objective has
been to determine if presumed products of this precursor are processed
coordinately following their synthesis. We have concentrated on two
peptides (ELH and the acidic peptide, AP) because they are most easily
identified in our analytical systems. On pulse-chase radiolabeling of the
cells in vitro, we found that labeled AP appears before labeled ELH in
axonal transport. This observation is not easily accounted for by the
assumption, taken from studies of other peptide-secreting cells, that a
precursor to both peptides is loaded into secretory granules before further
processing ensues. Since the initial disproportion in the representation of
the peptides in transport is no longer detectable at long chase times (18
and 24 hr), we examined the possibilities that ELH production is delayed
relative to that of AP or that AP is degraded more rapidly than ELH. No
evidence was found for either process. The disproportion between the newly
labeled peptides in transport was evident on analysis of the medium bathing
bag cells depolarized after 24 hr of chase.(ABSTRACT TRUNCATED AT 250
WORDS)