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PubMed2006

Acetylcholinesterase-ISFET based system for the detection of acetylcholine and acetylcholinesterase inhibitors.

A bioelectronic hybrid system for the detection of acetylcholine esterase (AChE) catalytic activity was assembled by way of immobilizing the enzyme to the gate surface of an ion-sensitive field-effect transistor (ISFET). Photometric methods used to characterize bonded enzyme and linker layers on silicon substrates confirm the existence of a stable amino-cyanurate containing AChE monolayer. The transduction of the enzyme-functionalized ISFET, in ionic solutions, is detected in response to application of acetylcholine (ACh). Recorded sensitivity of the modified ISFET to ACh has reached levels of up to 10(-5)M. The Michaelis-Menten constant of the immobilized AChE is only moderately altered. Nevertheless, the maximum reaction velocity is reduced by over an order of magnitude. The ISFET response time to bath or ionophoretic application of ACh from a micropipette was in the range of a second. The catalytic activity of the immobilized AChE is inhibited in a reversible manner by eserine, a competitive inhibitor of AChE. We conclude that the immobilized enzyme maintains its pharmacological properties, and thus the described bioelectronic hybrid can serve as a detector for reagents that inhibit AChE activity.

Acetylcholine↗
PubMed1986

An acetylcholinesterase-mediated density shift technique demonstrates that coated vesicles from chick myotubes may contain both newly synthesized acetylcholinesterase and acetylcholine receptors.

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.

Acetylcholinesterase↗
PubMed1981

Amniotic fluid acetylcholinesterase electrophoresis as a secondary test in the diagnosis of anencephaly and open spina bifida in early pregnancy. Report of the Collaborative acetylcholinesterase Study.

Fifteen centres collaborated in a study to determine the value of amniotic fluid acetyl cholinesterase (AChE) electrophoresis in the diagnosis of fetal open neural-tube defects (NTDs) between 13 and 24 weeks of gestation among women with positive amniotic fluid alpha-fetoprotein (AFP) results. Pregnancies with positive amniotic fluid AFP results were identified from about 34 000 tested; on average they had values greater than the 99.6th percentile for non-NTD pregnancies. Amniotic fluid samples were available from 1099 pregnancies with positive AFP results, and the percentages which yielded positive AChE results were as follows: anencephaly 99.6% (476/478); open spina bifida 99.4% (333/335); non-NTD pregnancies (i) without serious malformation and not ending in miscarriage 6% (8/125), (ii) without serious malformation but ending in miscarriage 47% (34/73), (iii) exomphalos 75% (47/63), (iv) congenital nephrosis 0% (0/11), (v) other serious malformations 50% (7/14). The gel-AChE test was thus found to be very effective when applied to amniotic fluid samples with positive AFP results, substantially reducing the number of false positives with only a very small loss in the detection of open neural-tube defects. Among women with positive amniotic fluid AFP results, the risk of having a fetus with an open NTD compared to having one without a serious malformation or a miscarriage is raised about 16-fold if the AchE test is also positive. The actual risk will depend on the birth prevalence and the reason for amniocentesis. For example, in the U.K. the risk of open spina bifida (expressed as an odds ratio) when both the amniotic fluid AFP result and the gel AChE results are positive would be as follows for women referred for amniocentesis in different categories; approximately 288:1 for those referred because of single raised serum AFP level (greater than or equal to 2.5 time the normal median at 16-18 weeks of gestation, 80:1 for women referred because of having previously had an infant with an NTD, and 8:1 for women referred for other reasons. It the amniotic fluid sample is stained with blood which is mainly fetal in origin, the corresponding odds are much lower (36:1, 10:1, and 1:1 respectively): if it is not blood-stained or is stained mainly with maternal blood, they are higher (954:1, 265:1, and 26:1 respectively).

Acetylcholinesterase↗
PubMed1983

Acetylcholinesterase in the ventrobasal thalamus: transience and patterning during ontogenesis.

In this study, maturational alterations in acetylcholinesterase-dependent staining of the thalamic ventrobasal complex of rat and mouse were examined. The study was undertaken to address the question of whether this nucleus exhibits transient acetylcholinesterase positivity during its development and whether the enzyme is likely to be synthesized by its immature intrinsic neurons. Also, the patterning due to acetylcholinesterase staining of cells and fibers, and the developmental changes in these patterns, have not been described in earlier work. In contrast to surrounding thalamic nuclei, the ventrobasal complex is acetylcholinesterase-positive at birth. In rat, acetylcholinesterase staining of the ventrobasal thalamus is still more intense than in adjacent nuclei at the end of the first week postnatally. Virtually all somata in the nucleus are filled with dense reaction product at this time. Ultrastructurally, reaction product is associated with the granular endoplasmic reticulum. At this stage, there is a marked difference in intensity of staining between the medial and lateral subdivisions of the nucleus, and patterned clustering of somata within each subdivision is readily appreciated in acetylcholinesterase-stained material. In the second postnatal week, intrinsic acetylcholinesterase activity is progressively lost. By the end of the third postnatal week, the nucleus is quite pale except for one area. In the posterior portion of the lateral subdivision, adjacent to the nucleus reticularis, interconnecting bundles of acetylcholinesterase-positive fibers enter the nucleus. They course medially in the lateral subdivision and break up into a plexus of fine fibers. The development of acetylcholinesterase-dependent staining patterns in the mouse is quite similar, except that histochemically detectable levels of enzyme are substantially lower in the neonatal period. It is concluded that the ventrobasal complex can be distinguished from other thalamic nuclei in regard to earlier onset and/or transience of acetylcholinesterase staining. Ultrastructural observations suggest that virtually all immature ventrobasal neurons are synthesizing acetylcholinesterase. It is suggested that the transient staining for enzyme is due primarily to alteration in synthesis and/or turnover in neurons of the ventrobasal complex. In addition, the acetylcholinesterase staining reveals a patterning of fibers and cells that also undergoes developmental alteration. Evidence is discussed suggesting that axons in the barrels of somatosensory cortex (SmI) are derived from these transiently acetylcholinesterase-positive somata. Consequently, the loss of acetylcholinesterase fiber staining in the barrels, during the third postnatal week (noted previously), may be related to a decrease in synthesis of enzyme in the neuronal somata of the ventrobasal complex.

Acetylcholinesterase↗