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Evidence Against an Acute Inhibitory Role of nSec‐1 (Munc‐18) in Late Steps of Regulated Exocytosis in Chromaffin and PC12 Cells
Author(s) -
Graham Margaret E.,
Sudlow Allan W.,
Burgoyne Robert D.
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.69062369.x
Subject(s) - exocytosis , secretion , regulator , chromaffin cell , microbiology and biotechnology , munc 18 , mutant , transfection , inhibitory postsynaptic potential , biology , cell culture , chemistry , biochemistry , endocrinology , synaptic vesicle , adrenal medulla , gene , vesicle , genetics , membrane , catecholamine
nSec‐1 (munc‐18) is a mammalian homologue of proteins implicated in constitutive exocytosis in yeast and neurotransmission in Caenorhabditis elegans and Drosophila . Mutant phenotypes in these species suggest that nSec‐1 is likely to be required for neurotransmission. Various other data have been interpreted as suggesting that nSec‐1 could also be a negative regulator of Ca 2+ ‐dependent exocytosis. We have tested this possibility by introducing exogenous nSec‐1 into permeabilised chromaffin or PC12 cells and examining its effects on Ca 2+ ‐induced and α‐soluble N ‐ethylmaleimide‐sensitive fusion protein attachment protein‐stimulated exocytosis. No effects of exogenous nSec‐1 were observed in these assays. In addition, the effect of nSec‐1 overexpression in transiently transfected PC12 cells on reporter growth hormone (GH) secretion was examined. Overexpression of nSec‐1 resulted in a marked increase in GH production, reflected in an increase in both cell‐associated and medium GH levels. The relative amounts retained in the cells were unaffected by nSec‐1 overexpression, indicating that GH storage was unaffected and that the major effect was on its synthesis. In contrast, nSec‐1 overexpression did not affect the proportion of GH that was released following stimulation in intact or permeabilised cells. These results suggest either that nSec‐1 is already expressed at sufficient levels and remains so following permeabilisation or that nSec‐1 may not be an acute inhibitory regulator of Ca 2+ ‐dependent exocytosis in chromaffin or PC12 cells.