Journal of Neuroscience, Vol 6, 3112-3119, Copyright © 1986 by Society for Neuroscience
An acetylcholinesterase-mediated density shift technique demonstrates that coated vesicles from chick myotubes may contain both newly synthesized acetylcholinesterase and acetylcholine receptors
K Porter-Jordan, RJ Benson, P Buoniconti and RE Fine
Coated vesicles isolated from 17 d chick embryo skeletal muscle contain
acetylcholine receptors (AChRs) as shown by the presence of specific,
latent binding sites for 125I-alpha bungarotoxin (125I-alpha-BTX). Since
these coated vesicles also contain AChE (Benson et al., 1985), we
hypothesized that a coated vesicle could carry both molecules: one an
integral membrane protein, the other a secreted protein. An AChE- mediated
density shift technique was used to obtain data that indicate that most
isolated coated vesicles contain AChE and that some contain AChRs as well.
Similar results were obtained with coated vesicles isolated from cultured
chick embryo myotubes treated briefly with diisopropylfluorophosphate (DFP)
to inactivate all preexisting AChE and allowed to synthesize AChE for 2 1/2
hr. These data are compatible with the hypothesis that both an integral
plasma membrane protein, AChR, and a secretory protein, AChE, traverse the
identical pathway after synthesis, as proposed by Rotundo and Fambrough
(1980a). We suggest that coated vesicles are important intermediates in the
exocytotic pathway, and that the large percentage of coated vesicles
utilized for exocytotic transport can explain the rapid net increase in
surface area achieved during myotube development. We also discuss the
potential utility of the AChE-mediated density shift in studying the
exocytotic and endocytotic pathways in other cell types, and possible
pitfalls associated with its use.