Isoenzymes of soluble and membrane-bound acetylcholinesterase in boine splanchnic nerve and adrenal medulla

Selective enhancement of the activity of C-terminally truncated, but not intact, acetylcholinesterase

Acetylcholinesterase (AChE) is one of the fastest enzymes approaching the catalytic limit of enzyme activity. The enzyme is involved in the terminal breakdown of the neurotransmitter acetylcholine, but non-enzymatic roles have also been described for the entire AChE molecule and its isolated C-terminal sequences. These non-cholinergic functions have been attributed to both the developmental and degenerative situation: the major form of AChE present in these conditions is monomeric. Moreover, AChE has been shown to lose its typical characteristic of substrate inhibition in both development and degeneration. This study characterizes a form of AChE truncated after amino acid 548 (T548-AChE), whose truncation site is homologue to that of a physiological form of T-AChE detected in fetal bovine serum that has lost its C-terminal moiety supposedly due to proteolytic cleavage. Peptide sequences covered by this C-terminal sequence have been shown to be crucially involved in both developmental and degenerative mechanisms in vitro. Numerous studies have addressed the structure-function relationship of the AChE C-terminus with T548-AChE representing one of the most frequently studied forms of truncated AChE. In this study, we provide new insight into the understanding of the functional characteristics that T548-AChE acquires in solution: T548-AChE is incubated with agents of varying net charge and molecular weight. Together with kinetic studies and an analysis of different molecular forms and aggregation states of T548-AChE, we show that the enzymatic activity of T548-AChE, an enzyme verging at its catalytic limit is, nonetheless, apparently enhanced by up to 800%. We demonstrate, first, how the activity of T548-AChE can be enhanced through agents that contain highly positive charged moieties. Moreover, the un-competitive mechanism of activity enhancement most likely involves the peripheral anionic site of AChE that is reflected in delayed substrate inhibition being observed for activity enhanced T548-AChE. The data provides evidence towards a mechanistic and functional link between the form of AChE unique to both development and degeneration and a C-terminal peptide of T-AChE acting under those conditions.

Rapid eye movement sleep deprivation induces an increase in acetylcholinesterase activity in discrete rat brain regions

Some upper brainstem cholinergic neurons (pedunculopontine and laterodorsal tegmental nuclei) are involved in the generation of rapid eye movement (REM) sleep and project rostrally to the thalamus and caudally to the medulla oblongata. A previous report showed that 96 h of REM sleep deprivation in rats induced an increase in the activity of brainstem acetylcholinesterase (Achase), the enzyme which inactivates acetylcholine (Ach) in the synaptic cleft. There was no change in the enzyme's activity in the whole brain and cerebrum. The components of the cholinergic synaptic endings (for example, Achase) are not uniformly distributed throughout the discrete regions of the brain. In order to detect possible regional changes we measured Achase activity in several discrete rat brain regions (medulla oblongata, pons, thalamus, striatum, hippocampus and cerebral cortex) after 96 h of REM sleep deprivation. Naive adult male Wistar rats were deprived of REM sleep using the flower-pot technique, while control rats were left in their home cages. Total, membrane-bound and soluble Achase activities (nmol of thiocholine formed min(-1) mg protein(-1)) were assayed photometrically. The results (mean +/- SD) obtained showed a statistically significant (Student t-test) increase in total Achase activity in the pons (control: 147.8 +/- 12.8, REM sleep-deprived: 169.3 +/- 17.4, N = 6 for both groups, P<0.025) and thalamus (control: 167.4 +/- 29.0, REM sleep-deprived: 191.9 +/- 15.4, N = 6 for both groups, P<0.05). Increases in membrane-bound Achase activity in the pons (control: 171.0 +/- 14.7, REM sleep-deprived: 189.5 +/- 19.5, N = 6 for both groups, P<0.05) and soluble enzyme activity in the medulla oblongata (control: 147.6 +/- 16.3, REM sleep-deprived: 163.8 +/- 8.3, N = 6 for both groups, P<0.05) were also observed. There were no statistically significant differences in the enzyme's activity in the other brain regions assayed. The present findings show that the increase in Achase activity induced by REM sleep deprivation was specific to the pons, a brain region where cholinergic neurons involved in REM generation are located, and also to brain regions which receive cholinergic input from the pons (the thalamus and medulla oblongata). During REM sleep extracellular levels of Ach are higher in the pons, medulla oblongata and thalamus. The increase in Achase activity in these brain areas after REM sleep deprivation suggests a higher rate of Ach turnover.

Hydrophobic protein that copurifies with human brain acetylcholinesterase: amino acid sequence, genomic organization, and chromosomal localization

The mechanism of attachment of acetylcholinesterase (AChE) to neuronal membranes in interneuronal synapses is poorly understood. We have isolated, sequenced, and cloned a hydrophobic protein that copurifies with AChE from human caudate nucleus and that we propose forms a part of a complex of membrane proteins attached to this enzyme. It is a short protein of 136 amino acids and has a molecular mass of 18 kDa. The sequence contains stretches of both hydrophobic and hydrophilic amino acids and two cysteine residues. Analysis of the genomic sequence reveals that the coding region is divided among five short exons. Fluorescence in situ hybridization localizes the gene to chromosome 6p21.32-p21.2. Northern blot analysis shows that this gene is widely expressed in the brain with an expression pattern that parallels that of AChE.

Choline acetyltransferase and acetylcholinesterase in the normal, developing and regenerating newt retinas

The presence of the choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) was demonstrated in the adult newt retina using immunocytochemical and histochemical techniques. Within the inner plexiform layer (IPL), two ChAT-positive bands were detected at relative depths of 0-15% and 45-60% of the total thickness (100%) of the IPL. AChE-positive band occupied approximately 0-60% of the IPL width with an intensive AChE-positive band at a depth of 20-40% within the IPL. Localizations of maximum ChAT and AChE activity were not exactly the same in the IPL of the mature retina. To elucidate whether retinal regeneration follows the same sequence of cellular differentiation steps that occur in retinal development, we examined the time course of appearance of the cholinergic neurons and AChE activity in both developing and regenerating retinas. The ChAT-positive cells were first detected in the retina just before or at the beginning of the morphological development of the IPL in both developing and regenerating retinas. AChE activity first became detectable in somata located at the most proximal layer of the retina before the ChAT-positive cells could be detected and well before the IPL developed in both developing and regenerating retinas. During subsequent development and regeneration, the outer plexiform layer, the IPL, and somata close to either side of the IPL became AChE-positive. The fact that the time course of the appearance of ChAT and AChE molecules during regeneration was similar to that observed during development suggests that common mechanisms may control both the development and the regeneration of the newt retina.

Rapid eye movement (REM) sleep deprivation reduces rat frontal cortex acetylcholinesterase (EC 3.1.1.7) activity

Rapid eye movement (REM) sleep deprivation induces several behavioral changes. Among these, a decrease in yawning behavior produced by low doses of cholinergic agonists is observed which indicates a change in brain cholinergic neurotransmission after REM sleep deprivation. Acetylcholinesterase (Achase) controls acetylcholine (Ach) availability in the synaptic cleft. Therefore, altered Achase activity may lead to a change in Ach availability at the receptor level which, in turn, may result in modification of cholinergic neurotransmission. To determine if REM sleep deprivation would change the activity of Achase, male Wistar rats, 3 months old, weighing 250-300 g, were deprived of REM sleep for 96 h by the flower-pot technique (N = 12). Two additional groups, a home-cage control (N = 6) and a large platform control (N = 6), were also used. Achase was measured in the frontal cortex using two different methods to obtain the enzyme activity. One method consisted of the obtention of total (900 g supernatant), membrane-bound (100,000 g pellet) and soluble (100,000 g supernatant) Achase, and the other method consisted of the obtention of a fraction (40,000 g pellet) enriched in synaptic membrane-bound enzyme. In both preparations, REM sleep deprivation induced a significant decrease in rat frontal cortex Achase activity when compared to both home-cage and large platform controls. REM sleep deprivation induced a significant decrease of 16% in the membrane-bound Achase activity (nmol thiocholine formed min-1 mg protein-1) in the 100,000 g pellet enzyme preparation (home-cage group 152.1 +/- 5.7, large platform group 152.7 +/- 24.9 and REM sleep-deprived group 127.9 +/- 13.8). There was no difference in the soluble enzyme activity. REM sleep deprivation also induced a significant decrease of 20% in the enriched synaptic membrane-bound Achase activity (home-cage group 126.4 +/- 21.5, large platform group 127.8 +/- 20.4, REM sleep-deprived group 102.8 +/- 14.2). Our results suggest that REM sleep deprivation changes Ach availability at the level of its receptors through a decrease in Achase activity.

Uptake of acetylcholinesterase by neurons in the substantia nigra

It is known that acetylcholinesterase is secreted by the dopaminergic neurons of the substantia nigra and has a subsequent action independent of cholinergic transmission. Although non-cholinergic actions of this protein have been demonstrated, the subsequent fate of acetylcholinesterase is unknown. One possibility is that acetylcholinesterase is taken up following secretion into the extracellular space. This hypothesis has been tested in vivo, in both conscious and anaesthetized guinea-pigs. Exogenous acetylcholinesterase (2-20 pM) was infused via a push-pull cannula implanted into either the substantia nigra or the surrounding extranigral regions: the amount subsequently recovered in the perfusate was then compared with control values. Only when the push-pull cannulae were implanted in the substantia nigra was there a marked decrease in the amount of acetylcholinesterase recovered; this selective retention was abolished when the perfusion medium was cooled to 4 degrees C or when the experiment was performed post mortem. Direct visualization of immunocytochemically identified nigral dopaminergic cells revealed co-localized deposits of labelled, exogenous acetylcholinesterase. Moreover, when exogenous acetylcholinesterase was boiled to prevent detection by the assay system and to eliminate any classical enzymatic action, an enhancement in perfusate levels of endogenous acetylcholinesterase was observed from nigral but not from extranigral sites, indicating that endogenous and exogenous acetylcholinesterases were in competition. These results suggest that, within the substantia nigra, secreted acetylcholinesterase may be subject to a temperature- and energy-dependent uptake mechanism.

Acetylcholinesterase activation of peritoneal macrophages is independent of catalytic activity

1. In diverse tissues, acetylcholinesterase appears to play a critical role in the functional state of cells completely dependent of cholinergic transmission. However, very little is known about the mechanisms and actual molecular structures mediating the fundamental interactions between this protein and the cellular membrane. 2. In this study, peritoneal macrophages were used as a model system to study the possible interaction between acetylcholinesterase, acting in a non-cholinergic capacity, and the cellular membrane. 3. When acetylcholinesterase was incubated with macrophages harvested from rat peritoneum, the rate of oxygen consumption was increased in a concentration-dependent manner that was independent of mitochondrial block with sodium cyanide. Furthermore, heat inactivation of enzymatic activity or application of BW 284C51 at a concentration which totally blocks catalytic activity did not eliminate the effect. 4. In contrast, incubation with bovine serum albumin or butyrylcholinesterase actually retarded oxygen consumption. 5. The effect of acetylcholinesterase depended on the presence of divalent cations and was inhibited by mannan and D-mannose, but not D-galactose. It is concluded that acetylcholinesterase can induce a "respiratory burst" in macrophages independent of its conventional catalytic site but involving either the mannose receptor of the monocyte-derived macrophage or a possible sugar binding site on acetylcholinesterase itself.

Presence of a soluble form of acetylcholinesterase in human ocular fluids

Samples of ocular fluid obtained from normal persons at necropsy and during eye surgery have been assayed for the presence of acetylcholinesterase. Measurable levels could be detected in all samples examined, but levels of acetylcholinesterase in vitreous humour were consistently higher than those in aqueous humour, indicating a possible retinal origin. Polyacrylamide gel electrophoresis revealed that the enzyme of ocular fluid had the same mobility as that of acetylcholinesterase from cerebrospinal fluid. It is probable that acetylcholinesterase is secreted from neuronal structures in the retina into the ocular fluid in an analogous manner to the secretion of acetylcholinesterase from brain neurones into cerebrospinal fluid.

Anomalous molecular form of acetylcholinesterase in cerebrospinal fluid in histologically diagnosed Alzheimer's disease

The possibility that the different molecular forms of acetylcholinesterase (AChE) in cerebrospinal fluid (CSF) which can be revealed by isoelectric focusing may reflect changes in AChE in pathologically affected neurons in Alzheimer's disease was tested in a retrospective study. CSF samples obtained at necropsy from 33 patients with clinically diagnosed dementia, 9 with possible dementia, and 19 without a diagnosis of dementia were examined by isoelectric focusing. An additional band indicating an anomalous molecular form of AChE was present in CSF from 19 of 23 patients with a histological diagnosis of Alzheimer's disease and no other central nervous system disorder but in none of the 19 non-demented patients (without a histological diagnosis of Alzheimer's disease). The band was also present in 2 of 8 patients with histologically defined Alzheimer's disease plus other neurological disorders and in 4 of 8 patients with possible dementia who did not meet histopathological criteria for Alzheimer's disease. The absence of the anomalous form of AChE from the CSF of non-demented patients and its presence in the CSF of the majority of patients with Alzheimer's disease has implications for our understanding of the biological basis of the disease and might form the basis of an antemortem diagnostic test.

A noncholinergic action of acetylcholinesterase (AChE) in the brain: from neuronal secretion to the generation of movement

1. In various brain regions, there is a puzzling disparity between large amounts of acetylcholinesterase and low levels of acetylcholine. One such area is the substantia nigra. Furthermore, within the substantia nigra, a soluble form of acetylcholinesterase is released from the dendrites of dopamine-containing nigrostriatal neurons, independent of cholinergic transmission. These two issues have prompted the hypothesis that acetylcholinesterase released in the substantia nigra has an unexpected noncholinergic function. 2. Electrophysiological studies demonstrate that this dendritic release is a function, not of the excitability of the cell from which the acetylcholinesterase is released, but of the inputs to it. In order to explore this phenomenon at the behavioral level, a novel system has been developed for detecting release of acetylcholinesterase "on-line." It can be seen that release of this protein within the substantia nigra can reflect, but is not causal to, movement. 3. Once released, the possible actions of acetylcholinesterase can be studied at both the cellular and the behavioral level. Independent of its catalytic site, acetylcholinesterase has a "modulatory" action on nigrostriatal neurons. The functional consequences of this modulation would be to enhance the sensitivity of the cells to synaptic inputs. 4. Many basic questions remain regarding the release and action of acetylcholinesterase within the substantia nigra and, indeed, within other areas of the brain. Nonetheless, tentative conclusions can be formulated that begin, in a new way, to provide a link between cellular mechanisms and the control of movement.

Acetylcholinesterase activity in regions of mouse brain following acute and chronic treatment with a benzodiazepine inverse agonist

1. Chronic administration of the benzodiazepine inverse agonist FG 7142 has previously been shown to induce seizure activity in mice. In the present study we have investigated the effects of acute and chronic treatment with FG 7142 in mice on the levels of acetylcholinesterase activity in cortex, hippocampus, midbrain and striatum. We have also investigated the effects of acute and chronic stress in the form of handling (vehicle-injection) on acetylcholinesterase levels. 2. A single dose of FG 7142 produced a marked elevation of total acetylcholinesterase activities in the hippocampus and midbrain when compared with vehicle-injected control levels, but the levels were not different from those in unhandled animals. 3. Acute stress, in the form of vehicle-injection produced decreases in cortical and hippocampal soluble acetylcholinesterase activity but FG 7142 had no effect upon these stress-induced changes. 4. Total cortical and hippocampal acetylcholinesterase activities were increased by 56% and 16% respectively in the chronic FG 7142-treated mice that exhibited seizure activity (compared with vehicle-injected controls). 5. Soluble acetylcholinesterase activity in the midbrain was decreased to 82% of control levels only in animals that had undergone FG 7142-induced kindling. Smaller or no changes in acetylcholinesterase activity in the midbrain were observed in chronically FG 7142-treated animals that exhibited no seizure activity. 6. Mice that did not demonstrate seizure activity in response to chronic FG 7142 treatment showed alterations in the soluble acetylcholinesterase activities of the hippocampus and midbrain. 7. It is concluded that chronic treatment with the benzodiazepine inverse agonist FG 7142 produces alterations in the acetylcholinesterase activities of various brain regions, in a manner related to the kindling that can be produced by this treatment. 8. Chronic mild stress, in the form of repeated handling (vehicle injection), induced changes in brain activity with decreases in total activity occurring in the cortex and hippocampus, and an increase in soluble acetylcholinesterase activity occurring in the midbrain. 9. All these stress-induced changes appeared to be prevented by administration of FG 7142 at the time of the stress. It would appear therefore that FG 7142 can prevent the effects of chronic stress on brain acetylcholinesterase activity.

Secretion of acetylcholinesterase and butyrylcholinesterase from the guinea-pig isolated ileum

1. Strips of longitudinal muscle from guinea-pig ileum, retaining Auerbach's plexus, were superfused with oxygenated Krebs solution. Addition of 50 mM KCl led to a pronounced Ca2+-dependent increase in the activities of both acetylcholinesterase and non-specific cholinesterase (butyrylcholinesterase) in the perfusate but with no change in lactate dehydrogenase activity. 2. No release of acetylcholinesterase, either spontaneous or K+-evoked was observed in tissue freed of the nerve plexus, although release of butyrylcholinesterase still occurred. 3. Carbachol induced a marked Ca2+-dependent increase in the release of acetylcholinesterase but had no effect on the release of butyrylcholinesterase or lactate dehydrogenase. This carbachol-evoked increase in acetylcholinesterase release was blocked by hexamethonium but not by atropine. 4. Four readily soluble molecular forms of acetylcholinesterase and three soluble molecular forms of butyrylcholinesterase were present in innervated longitudinal muscle strips, but insignificant amounts of acetylcholinesterase were detected in denervated strips of muscle. Only one of the four molecular forms of acetylcholinesterase was recovered in the perfusates. 5. It is concluded that acetylcholinesterase is secreted from the nerves of Auerbach's plexus in response to depolarizing stimuli or to nicotinic cholinergic stimulation, while butyrylcholinesterase is secreted from non-neural elements, possibly the longitudinal muscle cells, of guinea-pig ileum in response to a depolarizing stimulus.

Cholinesterases in blood plasma and tissues of rats treated with n-hexane or with its neurotoxic metabolite 2,5-hexanedione

Adult male rats were subjected to 4 weeks' respiratory treatment with n-hexane (5000 ppm, 16h/day, 6 days/week); motor conduction velocity was significantly decreased in tail nerves at all weekly intervals and did not approach normal values in the 4 weeks following interruption of treatment. Plasma acetylcholinesterase (AChE) levels were significantly increased at all weekly intervals during treatment (25-40%); 2 weeks after the end of treatment they had returned to baseline. Oral treatment with 2,5-hexanedione (HD) (1% in drinking water) caused a similar increase in plasma levels; this increase was statistically significant also when compared with pair-fed (PF) control rats. A sucrose density gradient analysis showed only one peak of AChE activity at approximately 10 S (as in normal plasma). The levels of butyrylcholinesterase were unaltered in plasma of both n-hexane-and HD-treated rats. Both the fast-contracting EDL and the slow-contracting soleus muscles lost weight in HD-treated rats with respect to free-fed (AL) and PF controls. AChE levels responded differently to HD treatment in the two muscle types: in EDL total extracts, AChE activity increased considerably with respect to AL controls (+ 70%, p less than 0.001), while the levels of the 16 S and 4 S molecular forms were unaltered. The increased levels of AChE found in plasma of rats intoxicated with n-hexane or with its metabolite HD may originate from muscle and correspond to an increased secretion of this molecular form.

Acetylcholinesterase activity in regions of rat brain following repeated administration of electroconvulsive shock

It has previously been shown that 30 min after administration of a single elec troconvulsive shock (ECS) to rats there is a marked decrease in both soluble and total acetylcholinesterase (AChE) activity in the midbrain and hippocampus. In the current study it has been shown that AChE activity is unchanged in these regions (apart from a small rise in soluble AChE in the hippocampus) 30 min after the final ECS of a series of 10 (once daily for 10 days). Twenty-four hours after the last ECS there was a significant increase in total and membrane bound AChE activity in the striatum but not hippocampus, midbrain, cortex and amygdala. This change in the striatum may be associated with the change in GABA synthesis which has been shown to also occur in this region at the same time.

Acetylcholinesterase activity in regions of the rat brain following a convulsion

The effects of electroconvulsive shock on the levels of acetylcholinesterase in several brain regions of the rat were studied. Hippocampus, mesencephalon, cortex, and striatum exhibited rapid changes in acetylcholinesterase activity during the first few minutes following the convulsion, whereas brainstem and basal forebrain levels remained unchanged. In both hippocampus and midbrain there was a sustained decrease in activity: the total acetylcholinesterase activity was decreased by up to 40% within 2 min of the convulsion and did not return to control values for another 3 h. Thirty minutes after a flurothyl-induced convulsion there was a similar fall in acetylcholinesterase activity in both these regions, whereas a subconvulsive electric shock produced no change. It is concluded that a convulsion produces significant short-term decreases in acetylcholinesterase activity in areas of the rat brain that are involved in the generation and propagation of seizures, and the question is raised of whether this is related to the increase in seizure threshold that follows a convulsion.

Determination of cholinesterase and acetylcholinesterase in amniotic fluid. Uses in prenatal diagnosis and quality control

The determination of acetylcholinesterase (AChE) has been shown to be as specific as alphafetoprotein (AFP) for the prenatal detection of open neural tube defects although AFP remains the method of choice. This paper describes a semi-automated technique for the analysis of acetylcholinesterase in amniotic fluid that: A) reduces the cost of the procedure; B) allows for a larger number of samples to be run at a time; and C) provides for more accurate and reproducible procedures and results. Six fetuses with neural tube defects (2 with gastroschisis and 3 where one twin was dead) were detected and found to have elevated AChE, TChE and 2 bands by electrophoresis. Quality control procedures using both pure enzyme and amniotic fluid with low and high levels of the enzyme are described. The analysis of 340 amniotic fluids of normal pregnancies indicates that the normal value for AChE is 5.17 +/- 2.63 mU/ml (97% confidence interval for the mean 4.84-5.49 mU/ml. A group of 27 abnormal pregnancies provides evidence that fetal vomiting and regurgitation, fetal demise, multiple cysts syndrome, idiopathic IUGR, arthrogryposis multiplex, hydrocephaly (stenosis of aqueductus), trisomy 21, trisomy 18, hydronephrosis, pyloric stenosis, heart malformation, ectopia cordis and multiple gestation produce elevated levels of pseudocholinesterase (PChE) in amniotic fluid. The use of pseudocholinesterase levels in amniotic fluid for prenatal diagnosis is proposed and discussed in view of its elevated levels in abnormal pregnancies where AChE is normal. The normal values for PChE are 23.86 mU/ml (mean) and 5.83 for standard deviation. Electrophoretic analysis was performed on all samples with values higher than one standard deviation above the mean.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal serum alpha-fetoprotein screening for neural tube defects. Report of a combined study in Germany and short overview on screening in populations with low birth prevalence of neural tube defects

The basis of maternal serum alpha-fetoprotein (AFP)-screening for neural tube defects is discussed. A report is given of a large scale screening study in the Federal Republic of Germany combining the experiences in Giessen and Hannover on over 50,000 pregnant women, about evenly distributed among both centers. Published and known forthcoming data from other low incidence populations, particularly of European countries, are reviewed briefly. The conclusion is reached that general screening could effectively be instituted and in the final result should also be cost-beneficial.

Reduced acetylcholine sensitivity in dystrophic mouse myotubes in vitro

Acetylcholine (ACh) sensitivity in cultured myotubes from normal or dystrophic mice was investigated using conventional techniques. Dystrophic multinucleate myotubes were found to be less responsive to the ACh with respect to the control preparation. Such a reduced sensitivity to ACh in dystrophic myotubes was accompanied by a reduced binding to 125I-alpha-bungarotoxin. The possible biological significance of these results on the muscle disease is discussed.

Acetylcholinesterase activity of adrenal chromaffin vesicles

Biochemical studies have given conflicting interpretations as to the localization of acetylcholinesterase within adrenal chromaffin cells. Previous histochemical studies found no reaction product on the chromaffin vesicles, although some biochemical studies suggest that a form of the enzyme is present. Sensitive histochemical procedures, with the appropriate controls, suggest a small amount of acetylcholinesterase is associated with chromaffin vesicles.

Evoked release of proteins from central neurons in vivo

Push-pull cannulae were implanted in both substantiae nigrae and caudate nuclei of the halothane-anesthetized cat. The release of total protein, acetylcholinesterase, and nonspecific cholinesterases was examined. Following direct application of potassium to one substantia nigra, changes occurred in the local release of total protein and acetylcholinesterase, but not nonspecific cholinesterases; changes also were observed in both caudate nuclei and the contralateral substantia nigra. The local evoked release of acetylcholinesterase and of total protein differed in the extent to which they were calcium-dependent. Control studies suggest that release of these compounds, both spontaneous and evoked, is related, at least in part, to neuronal activity. The significance of the neuronal release of proteins is discussed.

Measurement of cholinesterases in amniotic fluid using alpha naphthyl acetate as substrate: a possible initial test for prenatal diagnosis of open neural tube defects

A quantitative method for cholinesterases in amniotic fluid using the non-specific substrate alpha naphthyl acetate and the cholinesterase-specific inhibitor, eserine, is described. This assay was used to test 671 samples of amniotic fluid. The diagnoses for fetal ONTDs, based on the levels of AChE + ChE, were compared with those made for the same samples by the AFP method. Correct diagnoses were made by both methods with amniotic fluid from 35 women carrying fetuses with ONTDs and 631 carrying normal fetuses. There were five false-positive test results for normal fetuses by both methods when the cut-off points were 5 standard deviations above the mean for AFP and above the upper limit of the normal range (7.5 milliunits) for cholinesterase (AChE + ChE). None of the false-positive samples from either method had the acetylcholinesterase band of activity characteristic of ONTDs after gel electrophoresis. In addition to the above 671 samples, 37 pregnancies with serious fetal abnormalities other than ONTDs were tested. Two were identified by both the AFP and AChE + ChE methods, two more by AFP assay and one other by the AChE + ChE assay.

Acetylcholinesterase molecular forms from rat and human erythrocyte membrane

1. Some of the biochemical characteristics of acetylcholinesterase from rat and human erythrocytes were studied. 2. Both for rat and man two different acetylcholinesterase molecular forms were identified by gel electrophoresis. The faster moving form is less conspicuous and is not present in all individuals, therefore single-banded and double-banded preparations of red cell acetylcholinesterase can be obtained. The two components appear to be isomers of different molecular size (approximately Mr 150 000 and Mr 245 000) as estimated by gel electrophoresis at different polyacrylamide concentrations. 3. A single band, with a molecular weight of approximately 135 000, was obtained by sodium dodecyl sulphate gel electrophoresis. These results suggest that the faster moving form is a protomer and the slower a dimer. 4. The different sedimentation values obtained by density gradient centrifugation in the presence of Triton X-100 of double-banded (5.3S) and single-banded (6.3S) rat and human acetylcholinesterase preparations, are consistent with a protomer-dimer hypothesis. 5. The isoelectric pattern observed for both double- and single-banded preparations was similar for rat and man acetylcholinesterase and showed a considerable microheterogeneity (thirteen activity bands for rat and eleven for man with isoelectric values from 4.6 to 5.9).

Acetylcholinesterase activity and molecular forms during denervation and reinnervation in extensor digitorum longus muscle of the rat

The four principal molecular forms of acetylcholinesterase characteristic of the mammalian muscle (16.1 S., 12.5 S, 10.2 S, and 3.6. S) were identified by sucrose gradient sedimentation as the four activity peaks H, H1, M and L. After denervation obtained by crushing the sciatic nerve five stages of the denervation-reinnervation process were examined. Days 7, 14, 22, 30, and 60 were chosen on the basis of previous electrophysiological and histochemical studies. The AChE activity showed an initial drop followed by recovery after nerve arrival at the muscle which was completed by day 60. Marked changes in the relative proportions of the four molecular forms were observed. The 16.1 S almost disappeared during the denervation period, reappeared after nerve arrival and was completely restored at day 60. Changes were also observed in the intermediate and lower forms and were tentatively related to processes of degradation, reaggregation and de novo synthesis. A comparison of the present data with those from parallel electrophysiological and histochemical studies suggests the presence and the functional role of molecular forms other than 16S in the neuromuscular junction.

Particulate acetylcholinesterase in amniotic fluid and its implications for neural tube defect screening

Acetylcholinesterase activity in mid-trimester amniotic fluid has been determined by a quantitative spectrophotometric method and a qualitative electrophoretic technique in a limited (76 samples) retrospective study. Differential centrifugation studies on amniotic fluid from normal pregnancies demonstrated the presence of particle-associated acetylcholinesterase sedimenting only at relatively high centrifugal forces. It is postulated that this particle-associated activity was a contributory factor to an observed false-positive incidence of 6.6% when quantitative acetylcholinesterase measurement was used to discriminate between normal pregnancies and those associated with neural tube defects. Discrimination on the basis of electrophoretic analysis of acetylcholinesterase resulted in no misclassification of pregnancies. Particulate acetylcholinesterase would not be expected to influence the interpretation of the electrophoretic pattern due to its size-related exclusion from gel pores. The implication of these observations in the accurate prenatal diagnosis of neural tube defects is discussed.

Identification of aspirinase with one of the carboxylesterases requiring a thiol group

Aspirin-hydrolysing activity in guinea-pig liver is located mainly in the microsomal fraction. This activity was found by electrophoresis to be due to a single carboxylesterase band, out of 12 bands revealed with alpha-naphthyl acetate as substrate. The activity is inhibited completely and irreversibly by the carboxylesterase inhibitor bis-(-4-nitrophenyl) hydrogen phosphate, and also by thiol-blocking reagents.

In vitro interaction between bovine adrenal medullary cell membranes and chromaffin granules: specific control by Ca2+

The control of the in vitro interaction between bovine adrenal medullary plasma membranes and chromaffin granules by calcium has been studied. This interaction, which has previously been shown to result in the release of the soluble granular content, is a possible cell-free model for exocytosis. The plasma membrane-induced catecholamine release was stimulated when the [Ca2+] exceeded 2x10(-7) M. A maximal release was reached at 10(-5) M with a half maximal response around 10(-6)M. Mg2+ was not able to stimulate the system in the absence of Ca2+. These data suggest a high specificity of the calcium controlled exocytotic mechanism and the absence of an antagonism by high concentrations (10(-5)-10(-1) M) of magnesium at the exocytotic site itself.

Polyacrylamide gel electrophoresis of amniotic fluid cholinesterases: a good prenatal test for neural tube defects

The qualitative assay of the cholinesterases (ChE) in amniotic fluid on polyacrylamide gel gave a single major band (cholinesterase) in all samples from normal pregnancies, and two major bands (cholinesterase and acetylcholinesterase) in all cases from fetuses with open neural tube defects. Five fluids which were true false positive on alpha-fetoprotein (AFP) assay (elevated AFP in a clear fluid but normal fetus) had a single band, and two fluids which were false negative on AFP testing (normal AFP but spina bifida fetus) had two bands. The second 'diagnostic' ChE band sometimes occurred, together with other extra bands, in some fluids which were very severely contaminated by maternal or fetal blood, but in four of six fluids from normal fetuses where fetal blood staining was sufficient to cause the AFP to be elevated, there was only one ChE band. It is suggested that the qualitative assay of ChE should be performed in addition to AFP in the prenatal diagnosis of neural tube defects.

Production and release of acetylcholinesterase by a primary cell culture of bovine adrenal medullary chromaffin cells

Bovine adrenal chromaffin cells were isolated and maintained as primary culture monolayers. Total acetylcholinesterase (AChE) activity in the cells increased during the culture period, and AChE activity appeared in the culture medium. We have examined the role of the AChE synthesized by the cells on ACh-evoked release of catecholamine from the cells. A progressive decrease in the efficacy of ACh (5 X 10(-5) M) to evoke release of [3H]norepinephrine from day 3-15 cultures suggests that exogenously applied ACh is hydrolyzed by the nascent AChE synthesized by the cells. These findings provide evidence that chromaffin cells produce AChE and release it into their immediate environment.

Amniotic fluid acetylcholinesterase and prenatal diagnosis

Raised specific acetylcholinesterase (AChE) activity in amniotic fluid was consistently found to be associated with fetal intrauterine death and neural tube defects, but in just under half of the samples from pregnancies with spina bifida, the increase was marginal. Elevated AChE levels were occasionally found in fluid samples contaminated by maternal blood, and in nearly half of the samples which were a brown or yellow-brown colour but where there was a normal fetus. Nine fluids, five of which were contaminated with fetal blood, had a false positive result on alpha-fetoprotein (AFP) assay (elevated AFP levels and a normal fetus), but showed normal AChE activities. It is suggested that AChE estimation might be useful in prenatal diagnosis as a second test for those fluids which have an elevated AFP level.

Amniotic-fluid acetylcholinesterase as a possible diagnostic test for neural-tube defects in early pregnancy

Raised levels (greater than or equal to 4.5 munits/ml) of acetylcholinesterase (AChE) activity in amniotic fluid at 14--23 weeks of pregnancy were significantly associated with open fetal neural-tube defects. Out of 72 pregnancies correctly classified by the amniotic-fluid alpha-fetoprotein (A.F.P.) test, 2 of 56 without neural-tube defects and all 16 with open neural-tube defects (8 with anencephaly and 8awith open spina bifida) had raised levels of AChE. Out of 5 pregnancies misclassified by the A.F.P. test (4 without neural-tube defects and 1 with open spina bifida), only 1 was misclassified by the AChE test--namely, one of those without a neural-tube defect. Thus, only 3 of the 77 pregnancies tested were misclassified by the quantitative AChE test. A qualitative test for an isoenzyme of AChE found in cerebrospinal fluid correctly classified these 3 pregnancies. These findings suggest that the analysis of AChE in amniotic fluid may be a useful test in the diagnosis of open neural-tube defects.

Acetylcholinesterase in human amniotic fluid: An index of fetal neural development?

Acetylcholinesterase (AChE) activity was detected in amniotic fluid either sampled by amniocentesis at 14--23 weeks gestation or collected at normal parturition. Activity ranged from 0.2 to 8.9 u/l in the earlier samples and from 0.2 to 4.2 u/l in the later samples. Since the fetal but not the maternal serum contained AChE activity, we suggest that the AChE in the amniotic fluid is derived from the fetus. AChE is released from both neural and nonneural tissues, and the release of the enzyme from both sources may diminish as the nervous system matures. The amount of AChE found in amniotic fluid may be affected by abnormalities of the nervous system. Amniotic fluid from two fetuses with spina bifida contained AChE activity: one, with a gestational age of 21 weeks, was in the upper levels of the normal range (4.5 u/l), whereas the other, at 36 weeks, contained 1.9 times more activity than the next highest sample. In a 20-week fetus with anencephaly, the AChE activity in the amniotic fluid was increased 2.8-fold over the activity of the highest "normal" sample.

Diagnostic value of rectal mucosal acetylcholinesterase levels in Hirschsprung's disease

Acetylcholinesterase (AChE) activity was measured in rectal biopsy specimens obtained from 68 children aged between 2 days and 14 1/2 years in whom Hirschsprung's disease was suspected. The diagnosis was subsequently established in 12; in these, the mean AChE activity was found to be 30.5 X 10(-7) units/g tissue (range 16.9 to 63.0). The 56 non-Hirschsprung cases had a mean of 5.0 X 10(-7) units/g tissue (S.D. 2.2), the highest value in this group being 10.9. The results were unaffected by age, sex, nature of biopsy procedure, or the presence of blood. It is suggested that the assay of AChE activity in rectal biopsy material is a simple and quick procedure that is useful in the diagnosis of Hirschsprung's disease.

Molecular forms of cholinesterases in cerebrospinal fluid, blood plasma, and brain tissue of the beagle dog

In the present study we have investigated the activity of AChE and BuChE in the cisternal CSF of the Beagle dog and have outlined the characteristics of the molecular forms of both enzymes. The same enzymes were also investigated in samples from blood plasma and brain tissue. It is concluded that AChE in CSF originates from the spinal cord and brain tissues as a result of some secretory process. A combined origin from both blood plasma and brain tissue appears to be probable for the BuChE of the CSF.

Acetylcholinesterase activity in ventricular and cisternal CSF of dogs: effect of chlorpromazine

Acetylcholinesterase (AChE) activity in dog plasma is significantly higher than in either ventricular or cisternal CSF. However, since protein levels in plasma are about 100-fold higher than in CSF, the specific activity of AChE is lower in plasma than in CSF. Acetylcholinesterase activity in plasma represents only 22% of total cholinesterase (ChE) activity, while preliminary findings indicate that in ventricular CSF it is 50-60%. Acetylcholinesterase activity in ventricular CSF is significantly lower than in cisternal CSF. Chlorpromazine (10 mg/kg, intravenous), a drug which increases acetylcholine turnover, increased AChE-specific activity in all dogs. Our results support the hypothesis of a neuronal origin of AChE activity in CSF.

Release of acetylcholinesterase into the perfusate from the ox adrenal gland

Increasing the potassium ion concentration of Tyrode’s solution perfusing an isolated ox adrenal gland leads to a release of acetylcholinesterase activity into the perfusate. The amount of enzyme activity released by added potassium is much reduced if calcium ions are omitted from the perfusion fluid. The activity of acetylcholinesterase secreted into the perfusate was confined to a single isoenzyme which is identical with the only soluble isoenzyme present in splanchnic nerve trunks and with one of the five soluble isoenzymes in the adrenal medulla.