Multiple molecular forms of rat superior cervical ganglion acetylcholinesterase: developmental aspects in primary cell culture and during postnatal maturation in vivo

Phosphatidylinositol is involved in the attachment of tailed asymmetric acetylcholinesterase to neuronal membranes

1. We analyzed the mode of attachment of 16 S tailed acetylcholinesterase (AChE; EC 3.1.1.7) to rat superior cervical ganglion (SCG) neuronal membranes. Using extractions by high-salt (HS) and nonionic detergent (Triton X-100), we found two pools of 16 S AChE. 2. The detergent-extracted (DE) 16 S AChE was tightly bound to membranes through detergent-sensitive, high-salt insensitive interactions and was distinct from high-salt-soluble 16 S AChE. The detergent-extracted (DE) 16 S AChE constituted a significant proportion of about one-third of the total 16 S AChE. 3. Treatment of the neuronal membranes by a phosphatidylinositol-specific phospholipase C (PIPLC) resulted in the release of some, but not all DE 16 S AChE, indicating that a significant amount of the neuronal DE 16 S AChE, about one-third, is anchored to membranes through a phosphatidylinositol containing residue. Thus, a covalent association of a glycolipid and catalytic or structural AChE polypeptidic chains occurs not only for dimeric AChE but also for the asymmetric species of AChE. 4. The complex polymorphism of AChE is due not only to different globular or asymmetric associations of catalytic and structural subunits but also to the alternative existence of a transmembrane domain or a glycolipid membrane anchor.

Cell modulation of hydrophobic tailed 16S acetylcholinesterase by intracellular calcium in rat superior cervical ganglion neurons

In primary cell cultures of rat superior cervical ganglia (SCG) the tailed asymmetric 16S molecular form of acetylcholinesterase (AChE) possesses hydrophilic (high-salt soluble, HSS) and hydrophobic (detergent extracted, DE) variants. Hydrophobic tailed acetylcholinesterase is associated with membranes through a glycolipid anchor. In the presence of tunicamycin, an antibiotic which inhibits protein glycosylation, the cellular amount of the hydrophobic DE 16S AChE is increased. Exposure of the cells to the calcium ionophore A 23187 leads to a decrease in DE 16S AChE and a correlated increase in hydrophilic HSS 16S AChE. These results suggest the existence of an endogenous processing of tailed AChE, transforming the hydrophobic variant into an hydrophilic one controlled through glycosylation and intracellular calcium.

Cellular localization of the molecular forms of acetylcholinesterase in primary cultures of rat sympathetic neurons and analysis of the secreted enzyme

The secretion and cellular localization of the molecular forms of acetylcholinesterase (AChE) were studied in primary cultures of rat sympathetic neurons. When cultured under conditions favoring a noradrenergic phenotype, these neurons synthesized and secreted large quantities of the tetrameric G4, and the dodecameric A12 forms, and minor amounts of the G1 and G2 forms. When these neurons adopted the cholinergic phenotype, i.e., in the presence of muscle-conditioned medium, the development of the cellular A12 form was completely inhibited. These neurons secreted only globular, mainly G4, AChE. Both cellular and secreted A12 AChE in adrenergic cultures aggregated at an ionic strength similar to that of the culture medium, raising the hypothesis that this form was associated with a polyanionic component of basal lamina. In noradrenergic neurons, 60-80% of the catalytic sites were exposed at the cell surface. In particular, 80% of G4 form, but only 60% of the A12 form, was external, demonstrating for the A12 form a sizeable intracellular pool. The hydrophobic character of the molecular forms was studied in relation to their cellular localization. As in muscle cells, most of the G4 form was membrane-bound. Whereas 76% of the cell surface A12 form was solubilized in the aqueous phase by high salt concentrations, only 50% of the intracellular A12 form was solubilized under these conditions. The rest of intracellular A12 could be solubilized by detergents and was thus either membrane-bound or entrapped in vesicles originating from, e.g., the Golgi apparatus.

External and internal acetylcholinesterase in rat sympathetic neurones in vivo and in vitro

The subcellular distribution of multiple molecular forms of acetylcholinesterase (AChE) in neurones of rat superior cervical ganglion (SCG) was determined both in vivo and in vitro by the use of selective lipid-soluble or -insoluble inhibitors. In vivo as well as in vitro, 10 S AChE is mainly outside the cell. In primary cultures of rat SCG neurones, both 4 S and 16 S AChE are mainly inside the cell. In near-term rat SCG, 4 S and 16 S are more external to the cell than in primary cultures. In adult rat SCG, 4 S AChE is equally distributed inside and outside and 16 S AChE is mainly outside the cell. Thus, specific AChE externalization probably occurs in neuronal cells as a developmentally regulated process.

Modulation of the acetylcholine system in the superior cervical ganglion of rat: effects of GABA and hypoglossal nerve implantation after in vivo GABA treatment

gamma-Aminobutyric acid (GABA) was applied to the superior cervical ganglion (SCG) of CFY rats in vitro and in vivo, with or without implantation of a hypoglossal nerve, to evaluate the effects of these experimental interventions on the acetylcholine (ACh) system, which mainly serves the synaptic transmission of the preganglionic input. Long-lasting GABA microinfusion into the SCG in vivo apparently resulted in a "functional denervation." This treatment reduced the acetylcholinesterase (AChE; EC 3.1.1.7) activity by 30% (p less than 0.01) and transiently increased the number of nicotinic acetylcholine receptors, but had no significant effect on the choline acetyltransferase (acetyl-coenzyme A:choline-O-acetyltransferase; EC 2.3.1.6) activity, the ACh level, or the number of muscarinic acetylcholine receptors. The relative amounts of the different molecular forms of AChE did not change under these conditions. In vivo GABA application to the SCG with a hypoglossal nerve implanted in the presence of intact preganglionic afferent synapses exerted a significant modulatory effect on the AChE activity and its molecular forms. The "hyperinnervation" of the ganglia led to increases in the AChE activity (to 142.5%, p less than 0.01) and the 16S molecular form (to 200%, p less than 0.01). It is concluded that in vivo GABA microinfusion and GABA treatment in the presence of additional cholinergic synapses has a modulatory effect on the elements of the ACh system in the SCG of CFY rats.

Regulation of enzymes responsible for neurotransmitter synthesis and degradation in cultured rat sympathetic neurons. III. Effects of sodium butyrate

The effects of Na butyrate on the differentiation of newborn rat sympathetic neurons in primary cultures have been studied. Butyrate did not affect the long-term survival of these neurons in the presence of optimal concentrations of nerve growth factor, but decreased in a dose-dependent manner their protein content. In the range, 0.5-20 mM, butyrate did not modify the specific activity of lactate dehydrogenase in these cultures. Choline acetyltransferase activity developed at a 4.5- to 12-fold higher rate in cultures grown with 1-5 mM butyrate than in its absence. Concomitantly, tyrosine hydroxylase, dopa decarboxylase, dopamine-beta-hydroxylase, and acetylcholinesterase were depressed in cultures grown with butyrate. The deficit in acetylcholinesterase total activity was accompanied by an inhibition of the development of the asymmetric 16 S form of the enzyme. The deficit in tyrosine hydroxylase activity did not result from either a modification of the app Km for the enzyme's cofactor or a modification of its state of cAMP-dependent phosphorylation, but from a decrease in the number of immunoprecipitable enzyme molecules. A similar result was obtained with acetylcholinesterase. Butyrate thus reproduced in a qualitative manner the effects of a macromolecular factor purified from muscle conditioned medium on these neurons (J. P. Swerts, A. LeVan Thaï, A. Vigny, and M. J. Weber (1983) Dev. Biol. 100, 1-11; J. P. Swerts, Le Van Thai, and M. J. Weber (1984) 103, 230-234), raising the hypothesis of a common pathway in the regulation of neurotransmitter phenotype by these two agents.

Decrease of tailed, asymmetric 16S acetylcholinesterase in rat superior cervical ganglion neurons in vitro after potassium depolarization: partial antagonist action of a calcium-channel blocker

In primary cell cultures of rat superior cervical ganglia the tailed, asymmetric 16S molecular form of acetylcholinesterase (AChE) is preferentially decreased after potassium depolarization. This effect is not related to noradrenergic differentiation elicited by high potassium concentration. Moreover there is a partial antagonist action of a calcium-channel blocker, methoxyverapamil (D-600). These results suggest that membrane electrical activity exerts a regulatory control on AChE, and Ca2+ fluxes play an important role in regulatory events of AChE biosynthesis.

Regulation of enzymes responsible for neurotransmitter synthesis and degradation in cultured rat sympathetic neurons. II. Regulation of 16 S acetylcholinesterase by conditioned medium

The molecular forms of acetylcholinesterase (AcChE) have been studied in primary cultures of newborn rat sympathetic neurons grown either in the absence (CM- cultures) or in the presence (CM+ cultures) of muscle conditioned medium. The cultures were treated with a mitotic poison to eliminate non-neuronal cells. CAT activity increased with time in culture 4- to 20-fold faster in CM+ than in CM- cultures. In agreement with previous experiments (J.P. Swerts, A. Le Van Thaï, A. Vigny, and M.J. Weber, 1983, Develop. Biol. 100, 1-11), AcChE activity developed at a 3-fold lower rate in CM+ than in CM- cultures. This deficit in AcChE activity in CM+ cultures resulted from a deficit in the number of enzyme molecules immunoprecipitable with an antiserum raised against rat brain AcChE. In both types of cultures, AcChE forms were separated by sucrose gradient sedimentation into three main peaks corresponding to the 16 S and 10 S forms and a mixture of the 6.5 and 4 S forms. In 3-day-old CM+ and CM- cultures, the 16 S form represented 2% of the total activity. After 12-26 days, the percentage of 16 S form raised to 15-30% in CM- cultures, but remained lower than 5% in CM+ cultures. This difference was also observed when AcChE molecular forms were analyzed in the presence of protease inhibitors. A similar result was obtained by comparing cultures grown with and without a macromolecular factor partially purified from conditioned medium. These results suggest that an inverse relationship exists between the presence of 16 S AcChE and the presence of cholinergic synapses in these cultures.

Presynaptic modulation of activity and molecular forms of acetylcholinesterase in the rat superior cervical ganglion during early postnatal development

Preganglionic nerve trunk of the rat superior cervical ganglion was transected shortly after birth in order to evaluate the influence of preganglionic nerves on the development of acetylcholinesterase and choline acetyltransferase in ganglionic neurons. In spite of an early decentralization, specific activity of acetylcholinesterase in the ganglion is increasing during the first 3 wk of life until it is about equal to the activity which remains in the superior cervical ganglion decentralized in an adult animal. Thus, the preganglionic nerves, which per se contribute the presynaptic fraction of total ganglionic AChE activity in normal innervated ganglia, apparently exert no significant regulatory effect on the specific activity of the fraction of acetylcholinesterase affiliated with the developing ganglionic cells. However, the absence of innervation during development is strongly reflected in the pattern of acetylcholinesterase molecular forms. The activity of the 16 S molecular form of AChE remains high in the developing superior cervical ganglion, decentralized at birth, in contrast to the substantial absolute and relative decrease of specific activity of this form during development of a normally innervated ganglion. A high proportion of 16 S AChE probably reflects a shift of decentralized immature ganglion nerve cells toward a cholinergic character. In accordance with this assumption, choline acetyltransferase activity in early decentralized ganglia is significantly higher than that in the ganglia decentralized in adult animals.