Density dependent regulation of growth in L cell suspension cultures. 3. Elevation of specific activity of acetylcholinesterase

Properties of growth-related acetylcholinesterase in a cell line of fibroblastic origin

We have previously reported the presence and regulation of an acetylcholine-hydrolyzing enzyme in high density suspension cultures of WRL-10A fibroblasts where its activity increases 100-fold when growth is arrested. Substrate specificity, substrate inhibition, and product identification studies indicate that this enzyme is acetylcholinesterase (AChE, EC 3.1.1.7). Treatment of whole cells with 5 mM diazotized sulfanilic acid revealed that most of the AChE is located on the external surface of the cell membrane. It was also found that the enzyme is released in the medium at a rate of 0.5 U/h/mg cell protein and that within a 24-h period the de novo synthesized and liberated AChE is equivalent to 90% of the activity associated with the cells. No similar synthesis of AChE was found in six order fibroblastic cell lines examined. These and related findings indicating that acetylcholine is also present in high density populations of WRL-10A cells suggest that this unique phenotype may be used profitably in exploring further the relationship between components of the cholinergic system and non-neuronal cell growth.

The influence of cholinoceptor activity on the mitotic rate in the crypts of Lieberkühn in rat jejunum

1. The influence of cholinoceptor stimulation and cholinoceptor blockade on the mitotic rate in epithelial cells lining the crypts of Lieberkühn in rat jejunum was studied. 2. Cholinoceptor stimulation, either by injection of carbachol or by inhibition of acetylcholinesterase enzymes resulted in an increase in the mitotic rate. This increase in mitotic rate was blocked by tubocurarine, but not by atropine or hexamethonium. Atropine by itself increased the mitotic rate whereas tubocurarine alone or hexamethonium along decreased the mitotic rate. 3. The influence of atropine on crypt cell proliferation appears to involve an adrenergic mechanism since it is blocked by phentolamine.

Analysis of the forms of acetylcholinesterase from adult mouse brain

The solubilization of 80% of the acetylcholinesterase activity of mouse brain was performed by repeated 2h incubations of homogenates at 37 degrees C in an aqueous medium. Analysis of the soluble extract by gel filtration on Sephadex G-200 showed that up to 80% of the enzyme activity was eluted in a peak which was estimated to consist of molecules of about 74000mol.wt. This peak was called the monomer form of the enzyme. After 3 days at 4 degrees C, the soluble extract was re-analysed and was eluted from the column in four peaks of about 74000, 155000, 360000 and 720000 mol.wt. Since the total activity of the enzyme in these peaks was the same as that in the predominantly monomer elution profile of fresh enzyme, we concluded that the monomer had aggregated, possibly into dimers, tetramers and octomers. Extracts of the enzyme were analysed by polyacrylamide-gel electrophoresis and the resulting multiple bands of enzyme activity on gels were shown to separate according to their molecular sizes, that is by molecular sieving. All these forms had similar susceptibilities to the inhibitors eserine, tetra-isopropyl pyrophosphoramide and compound BW 284c51 [1,5-bis-(4-allyldimethylammoniumphenyl)pentan-3-one dibromide]. Thus the forms of the enzyme in mouse brain which can be detected by gel filtration and polyacrylamide-gel electrophoresis may all be related to a single low-molecular-weight form which aggregates during storage. This supports similar suggestions made for the enzyme in other locations.