Electrocatalytic microelectrode detectors for choline and acetylcholine following separation by capillary electrophoresis

Two electrocatalytic enzyme modified microelectrode systems were employed as end-column amperometric detectors of choline (Ch) and acetylcholine (ACh) following separation by capillary electrophoresis (CE). Horseradish peroxidase cross-linked in an osmium based redox polymer hydrogel (HRP-Os) was physically adsorbed on Au microelectrodes followed by chemical cross-linking of the enzymes acetylcholinesterase (AChE) and choline oxidase (ChO). An alternative approach utilized the deposition of the transition metal catalyst, Prussian Blue (PB), on Pt microelectrodes as the electrocatalyst. Utilizing butyrylcholine (BuCh) as an internal standard, the HRP-Os/AChE-ChO and PB/AChE-ChO electrodes exhibited excellent linear responses from 2-2000 microM and 10-2000 microM, respectively, for both Ch and ACh. Detection limits of 0.1 microM or 38 amol were determined for the HRP-Os/AChE-ChO electrode. The limit of detection for ACh and Ch at the PB/AChE-ChO electrode was 5 microM or 9.5 fmol. The electrodes were operated at potentials of +0.10 and -0.10 V vs Ag/AgCl (3 M NaCl), respectively, and thus minimized the potential response from oxidizable interferences. In addition, both electrocatalytic electrodes showed good operational stability for more than 70 h. The enhanced detection capability of the HRP-Os/AChE-ChO and PB/AChE-ChO electrodes in combination with efficient CE separation of Ch and ACh provides a new sensitive and selective strategy for monitoring and quantifying these cholinergic biomarkers in biological fluids.

Acetylcholinesterase inhibitors from the twigs ofvaccinium oldhami miquel

In the course of finding Korean natural products with acetylcholinesterase (AChE) inhibitory activity, we found that a methanolic extract of the twigs of Vaccinium oldhami significantly inhibited AChE. Bioassay-guided fractionation of the methanolic extract resulted in the isolation of two compounds, taraxerol (1) and scopoletin (2), as active constituents. These compounds inhibited AChE activity in a dose-dependent manner, and the IC50 values of compounds 1 and 2 were 33.6 (79 microM) and 10.0 (52 microM) microg/mL, respectively.

Rational design of biologically important chemosensors: a novel receptor for selective recognition of acetylcholine over ammonium cations

[structure: see text] In consideration of competition between cation-pi and hydrogen bond interaction forces, we designed a novel receptor, 1,3,5-tris(pyrrolyl)benzene, which shows high selectivity for acetylcholine (ACh). The selectivity of the receptor for ACh over other ammonium cations is demonstrated by the ion-selective electrode (ISE) method in buffer solution. The binding free energy of the receptor with ACh in chloroform solution is measured to be 3.65 kcal/mol in the presence of chloride anion by nuclear magnetic resonance spectroscopy, and that in water is estimated to be much greater ( approximately 6 kcal/mol).

Nonaqueous capillary electrophoresis with indirect electrochemical detection

Nonaqueous capillary electrophoresis (NACE) which makes use of organic solvents in place of conventional aqueous electrophoresis buffers is gaining increasing importance among modern separation techniques. Recently, it has been shown that amperometric detection in conjunction with acetonitrile-based NACE offers an extended accessible potential range and an enhanced long-term stability of the amperometric responses generated at solid electrodes. The present contribution takes advantage of the latter aspect to develop reliable systems for NACE with indirect electrochemical detection (IED). In this context, several compounds such as (ferrocenylmethyl)trimethylammonium perchlorate, tris(1,10-phenanthroline)cobalt(III) perchlorate and bis(1,4,7-triazacyclononane)nickel(II) perchlorate were studied regarding their suitability to act as electroactive buffer additives for IED in NACE. The performance characteristics for the respective buffer systems were evaluated. Tetraalkylammonium perchlorates served as model compounds for the optimization of the NACE-IED system. Target analytes choline and acetylcholine could easily be separated and determined by means of NACE-IED. In the case of a buffer system containing 10(-4) M tris(1,10-phenanthroline)cobalt(III) perchlorate the limits of detection were 2.5 x 10(-7) M and 4.6 x 10(-7) M for choline and acetylcholine, respectively. With the elaborated analytical procedure choline could be determined in pharmaceutical preparations.

Autonomic effects of some scorpion venoms and toxins

1. The autonomic effects of venoms and toxins from several species of scorpions, including the Indian red scorpion Mesobuthus tamulus, the Chinese scorpion Buthus martensi Karsch and the Israeli scorpion Leiurus quinquestriatus quinquestriatus, all belonging to Buthidae, and the Asian black scorpions Heterometrus longimanus and Heterometrus spinifer, belonging to Scorpionidae, are reviewed. 2. The effects of the venoms of M. tamulus and L. q. quinquestriatus on noradrenergic and nitrergic transmission in the rat isolated anococcygeus muscle revealed that both venoms mediated their pharmacological effects via a prejunctional mechanism involving the activation of voltage-sensitive sodium channels with consequent release of neurotransmitters that mediate target organ responses, similar to the effects mediated by other alpha-scorpion toxins. 3. Two new toxins, Makatoxin I and Bukatoxin, were purified to homogeneity from the venom of B. martensi Karsch. Determination of their complete amino acid sequences confirmed that both toxins belonged to the class of alpha-scorpion toxins. The effects of both toxins on noradrenergic and nitrergic transmission in the rat anococcygeus muscle provided firm evidence that their pharmacological actions also closely resembled those mediated by other alpha-scorpion toxins on neuronal voltage-sensitive sodium channels. 4. The venoms of H. longimanus and H. spinifer were found to have high concentrations of noradrenaline (1.8 +/- 0.3 mmol/L) and relatively high concentrations of acetylcholine (79.8 +/- 1.7 micromol/L) together with noradrenaline (146.7 +/- 19.8 micromol/L), respectively, which can account for their potent direct cholinergic and noradrenergic agonist actions in the rat anococcygeus muscle. 5. Our studies confirmed that the rat anococcygeus muscle is an excellent nerve-smooth muscle preparation for investigating the effects of bioactive agents on noradrenergic and nitrergic transmission, as well as the direct agonist actions of these agents on post-synaptic alpha-adrenoceptors and M3 muscarinic cholinoceptors. Although many studies, including our own, have documented that scorpion venoms and toxins mediate their primary effects via a prejunctional mechanism that leads to the marked release of various autonomic neurotransmitters, our studies have shown that there are exceptions to this generally accepted phenomenon. In particular, we have provided firm evidence to show that the venoms from H. longimanus and H. spinifer do not have such a prejunctional site of action but, instead, the venoms mediate their autonomic effects through direct agonist actions on post-junctional muscarinic M3 cholinoceptors and alpha-adrenoceptors.

Effect of Mg(2+)-ATP on acetylcholinesterase of Electrophorus electricus (L.)

The effect of Mg(2+)-ATP on purified acetylcholinesterase (AChE) from electric tissue of Electrophorus electricus (L.) was studied. The enzymatic activities were measured with acetylcholine and acetylthiocholine as substrates. The kinetic parameters Vmax, Km and Hill coefficient (nH), for acetylcholine and acetylthiocholine were modified with Mg(2+)-ATP. It was shown that acetylcholinesterase presents an apparent activation at high concentration of substrates and an inhibition in the presence of Mg(2+)-ATP at low concentration of acetylcholine and acetylthiocholine. In addition, the data suggest that Mg(2+)-ATP induced an allosteric modulation of the acetylcholinesterase obtained from Electrophorous electricus (L.), and indicate an active adenosine triphosphate participation during cholinergic activity.

Single cells as biosensors for chemical separations

A biosensor system based on the response of living cells was demonstrated that can detect specific components of a complex mixture fractionated by a microcolumn separation technique. This system uses ligand-receptor binding and signal-transduction pathways to biochemically amplify the presence of an analyte after electrophoretic separation. The transduced signal was measured by means of two approaches: (i) fluorescence determination of intracellular calcium concentrations in one or more rat PC-12 cells and (ii) measurement of transmembrane current in a Xenopus laevis oocyte microinjected with messenger RNA that encodes a specific receptor. This analysis system has the potential to identify biologically active ligands present in a complex mixture with exceptional sensitivity and selectivity.

Release and synthesis of acetylcholine at ectopic neuromuscular junctions in the rat

1. The ability of axons in the superficial fibular nerve to synthesize and release acetylcholine (ACh) has been studied before and after the formation of ectopic neuromuscular junctions (NMJs) with denervated soleus muscles of adult rats. 2. The central end of the severed fibular nerve was transplanted to the surface of the soleus muscle. After 3.5-5 weeks the soleus muscle was denervated in one group of rats by cutting the tibial nerve, allowing the formation of functional ectopic NMJs within a few days. In other rats the tibial nerve remained intact, preventing the formation of functional ectopic NMJs. 3. A month later the content of ACh, the levels of activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), and the amount of ACh released by depolarization by exposure to 50 mM KCl were measured in segments of isolated muscles that (i) contained normal or ectopic NMJs, (ii) were free of nerve or (iii) contained nerve that had not made NMJs. 4. Regions of muscles with ectopic nerve growth in which new NMJs had not formed contained substantial amounts of ACh and ChAT but no AChE. No detectable release of ACh could be evoked from these regions. 5. In muscles in which ectopic NMJs had formed after cutting the tibial nerve, the amounts of ACh and ChAT were about one-fifth of those in the regions of innervation of control muscles. ACh release could be evoked from the region of ectopic nerve growth in amounts nearly as great as those released from NMJs in normal and contralateral control muscles. 6. We conclude that the ability of the terminal parts of mature motor axons to synthesize and store ACh is largely independent of functional contact with muscle fibres. By contrast, the ability to release ACh in substantial amounts only develops when NMJs are formed. The possible significance of this situation for the development of synapses is discussed.

Improved method for the routine analysis of acetylcholine release in vivo: quantitation in the presence and absence of esterase inhibitor

An improved high-performance liquid chromatographic (HPLC) method using electrochemical detection (ED) is described capable of routinely measuring the low levels of acetylcholine (ACh) typically found in rat brain microdialysis samples. Microdialysis was performed in the striatum of the urethane anesthetized rat using a 4-mm membrane length, high recovery (40% at 1.0 microliters/min; ambient conditions), loop-design probe perfused with an artificial cerebrospinal fluid (aCSF) solution containing physiologically normal calcium levels (1.2 mM). The HPLC method utilizes a polymeric stationary phase to resolve choline (Ch) from ACh. These analytes are then converted to hydrogen peroxide (H2O2) by a solid-phase reactor (containing immobilized choline oxidase and acetylcholinesterase enzymes). The H2O2 is detected amperometrically and quantitated on a platinum (Pt) working electrode (+300 mV; with a unique analytical cell featuring a solid-state palladium reference electrode). Two designs of the Pt working electrode were examined, differing only in the support material used (Kel-F or PEEK). The Kel-F/Pt electrode had a limit of detection (LOD) for both analytes of < 30 fmol per 10 microliters with a signal-to-noise ratio of 3:1. Striatal microdialysis perfusates were monitored for ACh and Ch over a 0-1000 nM range of neostigmine (NEO) in the CSF perfusion medium. Using the 4-mm probe, basal ACh and Ch levels were detected with a NEO level as low as 10 nM and were found to be 37 +/- 3 fmol and 22 +/- 1 pmol per 10 microliters (mean +/- S.E.M., n = 6 replicates) respectively. In similar experiments using 3-mm concentric probes comparable (lower) levels of ACh were found with the 50 and 1000 nM NEO doses (n = 4-21 animals). ACh could not be reliably quantitated when animals were perfused with the 10 nM dose of NEO (n = 4). The PEEK/Pt electrode had an improved LOD of < 20 fmol per 10 microliters due to a two- to three-fold decrease in the background noise component. Basal striatal levels of ACh in the absence of NEO approached the LOD and were found to be 15 +/- 2 fmol per 10 microliters; Ch was 5 +/- 1 pmol per 10 microliters (n = 2, mean of five basal samples). The analytical system requires very little maintenance; a simple electrochemical electrode cleaning step eliminates the need for routine polishing of the Pt electrode and the mobile phase is stable for up to one week.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of acetylcholine release in the hippocampus by 6R-L-erythro-5,6,7,8-tetrahydrobiopterin is mediated by 5-hydroxytryptamine

Recently, we reported that 6R-L-erythro-tetrahydrobiopterin (6R-BH4), a natural cofactor for L-aromatic amino acid hydroxylases, enhances in vivo release of acetylcholine (ACh) in the rat hippocampus: the enhancement was abolished after depletion of brain catecholamines and 5-hydroxytryptamine (5-HT) by pretreatment with reserpine. In the present study, we have used in vivo brain microdialysis to clarify the neuronal mechanism involved in the enhancement of ACh release by 6R-BH4. After depletion of catecholamines by pretreatment of rats with alpha-methyl-p-tyrosine, 6R-BH4 added to the perfusion fluid still induced an increase in extracellular ACh levels monitored by microdialysis as an index of ACh release. In contrast, after depletion of 5-HT by pretreatment with p-chlorophenylalanine, most of the 6R-BH4-induced enhancement was eliminated. Exogenous 5-HT and dopamine (DA) but not noradrenaline added to the perfusion fluid stimulated ACh release with 5-HT being far more potent. Intraperitoneal administration of 5-hydroxytryptophan and L-DOPA also enhanced ACh release, presumably by their conversion to 5-HT and catecholamines, respectively. Administration of 6R-BH4 increased hippocampal 5-HT release, as indicated by increased extracellular levels of the major 5-HT metabolite, 5-hydroxyindoleacetic acid. These results suggest that 6R-BH4 stimulates ACh release in the hippocampus, mainly by augmenting release of 5-HT, a potent stimulator of ACh release, and partly by augmenting release of DA.

[Assessment of the activity of choline acetyltransferase in heart tissues]

A procedure is described for the radioisotope assay of acetylcholine transferase activity (EC 2.3.1.6), which involved specific synthesis of acetylcholine in vivo. Bromine acetylcholine was used as an inhibitor of the enzyme; 14C-AcCoA was used as a substrate and product of the enzymatic reaction. 14C-acetylcholine was separated from the substrate by means of anion exchange chromatography. The procedure described was 5 times more sensitive than the methods developed by F. Fonnum (1975) and S. Tucek (1983) being similarly reproducible. The assay was tested in experiments with rats under various conditions of hyperbaric oxygenation, in simulation of myocardial infarction as well as in moderate immobilization stress. The findings suggest that estimation of the acetylcholine transferase activity may be involved in complex evaluation of the cholinergic system state in tissues, which is essential for the study of pathogenesis of their dysfunctions and development of respective approaches to eliminate these impairments.

Characterization of prejunctional muscarinic autoreceptors in the guinea-pig trachea

1. The effects of ten muscarinic antagonists on electrically evoked [3H]-acetylcholine release and muscle contraction were compared in an epithelium-free preparation of the guinea-pig trachea that had been preincubated with [3H]-choline. 2. The M3-selective antagonists UH-AH 37, 4-diphenyl-acetoxy-N-piperidine methobromide and para-fluorohexahydrosiladiphenidol were more potent in reducing the contractile response than in facilitating the evoked [3H]-acetylcholine release. Hexahydrosiladiphenidol did not discriminate between pre- and postjunctional effects. The rank order of the postjunctional potencies of the ten antagonists as well as the postjunctional pA2 values obtained for hexahydrosiladiphenidol (7.95) and AQ-RA (7.08) identified the muscular receptor as an M3 subtype. 3. The M2-selective antagonists methoctramine, AF-DX 116 and AQ-RA 741 were more potent in facilitating the evoked [3H]-acetylcholine release than in inhibiting the contractile response. The increase in release by low concentrations of methoctramine, AF-DX 116 and AQ-RA 741 was paralleled by an enhancement of the stimulation-evoked contractions. 4. Comparison of the pre- and postjunctional potencies of the M1-, M2- and M3-selective antagonists suggests that autoinhibition of acetylcholine release is mediated via an 'M2-like' receptor which differs from the cardiac type M2 receptor in its relatively high affinity for hexahydrosiladiphenidol.

[A neurochemical study on brain cholinergic neuron; a newly improved pyrolysis gas chromatography/mass spectrometry (PY/GC/MS) method and its application]

A new method for measuring the endogenous acetylcholine (ACh) and choline (Ch) levels using a PY/GC/MS was established, and then the alteration of cholinergic neurons in the iminodipropionitrile (IDPN) induced dyskinesia model rat brain was studied. In performing the determinations of small amounts of brain ACh and Ch levels using a curie point PY/GC/MS, the following points were improved upon in the present study: 1) We shortened the distance between the sample tube and injection port allowing the rapid transformation to an analytical system without sub-reaction and re-synthesis of demethylated products. 2) The suitable pyrolytic temperature (curie point) was adjusted to 333 degrees C. 3) Then the aqueous sample (2 microliters) was wrapped in a pyrofoil with a curie point of 333 degrees C followed by drying at 80 degrees C. Subsequently, the pyrofoil was formed by a 200 kgf/cm2 press. 4) A fused silica capillary column (DB-5) was used instead of a pre-packed column (Jenden Phase). By these improvements, both calibration curves of ACh and Ch have high linearities (r = 0.988) between 1 pmol and 2 pmol, and the apparent peak of quasi-molecular ion and less fragment ion of each Ch analog was obtained. In the globus pallidus, caudate nucleus, hippocampus and cerebellum of IDPN induced dyskinesia model rats, remarkable reductions of ACh levels were observed using our newly improved PY/GC/MS method. Thus, our improved method can be utilized for measuring ACh levels in small discrete brain regions.

Turnover rate of brain acetylcholine using HPLC separation of the transmitter

A simple, reliable method was developed for measuring brain acetylcholine (ACh) turnover using HPLC methodology. Mice were injected intravenously with [3H]choline ([3H]Ch), and the turnover rate of ACh was calculated from the formation of [3H]ACh. Ch and ACh were separated from phosphorylcholine and from other radioactive compounds using tetraphenylboron extraction and counterion/reverse-phase chromatography. Endogenous Ch and ACh were quantified electrochemically through hydrogen peroxide production in a postcolumn reactor containing covalently bonded ACh esterase and Ch oxidase. Labeled Ch and ACh were quantified in the same sample by collecting the chromatographic fractions for radioactive content determinations. The method is rapid, well adapted to large series, and highly reproducible, with recoveries of 72.1% for Ch and 79.3% for ACh. The turnover value in mouse cerebral hemispheres was 16.02 nmol g-1 min-1 and decreased to 9.94 nmol g-1 min-1 in mice treated with oxotremorine.

An extract of lionfish (Pterois volitans) spine tissue contains acetylcholine and a toxin that affects neuromuscular transmission

A soluble toxic extract derived from spine tissue of the lionfish (Pterois volitans) decreased heart rate and force of contraction in isolated clam and frog hearts. These actions were due to the presence of micromolar concentrations of acetylcholine in the extract. Toxicity was retained after hydrolysis of acetylcholine by exogenous acetylcholinesterase, but heart function was no longer affected. Toxin treated in this way induced muscle fibrillation in an isolated nerve-muscle preparation, followed by blockade of neuromuscular transmission. Bursts of transient depolarizations were recorded at the muscle endplate shortly after toxin addition that correlated in time with the duration of toxin-induced muscle fibrillation. These effects are thought to be due to the increased release and then depletion of acetylcholine from the nerve terminal.

Isolation of choline and choline esters from Krebs-Ringer solution for gas chromatographic determination

A simple and efficient novel method for isolating picomole amounts of choline and choline esters in milliliter volumes of Krebs-Ringer solution has been developed. The procedure is based on the observation that the solubility of choline esters in acetonitrile is 10(4)-10(5) times higher than that of the inorganic salt constituents of Krebs-Ringer solution. The glucose content of the medium, which prevented the one-step isolation of choline esters based on acetonitrile extraction from its lyophilizate, was removed using Amberlite CG-50 column chromatography. Bound compounds to the column were eluted in 0.25 N HCl and lyophilized. The lyophilizate was extracted with acetonitrile, which was then decanted and eliminated by evaporation to dryness. The resultant glucose and salt-free residue can be assayed by gas chromatography. Total recoveries of added choline and choline esters over the entire isolation procedure, measured isotopically and/or gas chromatographically, were 93 and 97%, respectively. Due to the high and close-to-equal recoveries of choline esters, and the high purity of the final product, this procedure is suitable for estimating acetylcholine and choline in neural tissue perfusates by gas chromatography, as was demonstrated by this method using hippocampal slices.

Separation and quantification of choline and acetylcholine by thermospray liquid chromatography/mass spectrometry

The development of sensitive analytical techniques for use in the identification and qualification of molecules of biological origin remains a constant challenge. Often the compounds of interest are present in a complex mixture and require extensive sample preparation prior to analysis. Thermospray liquid chromatography/mass spectrometry (LC/MS) has been shown to be a method which allows for both separation of target molecules from complex mixtures and sensitive specific detection using a mass spectrometer. In this work thermospray LC/MS is used for the direct detection of intact, underivatized choline and acetylcholine from mouse brain homogenate. The results of our analysis corroborate previous analyses using a variety of indirect measurement techniques and thereby show that this simple direct analysis has wide potential applicability.

The lipid and protein content of cholinergic synaptic vesicles from the electric organ of Torpedo marmorata purified to constant composition: implications for vesicle structure

The lipid, protein, acetylcholine and ATP content of cholinergic synaptic vesicles isolated from the richly innervated electric organ of Torpedo marmorata and purified to constant composition has been determined. The number of vesicles present in the preparations has been estimated by quantitative electron microscopy and the mean composition of the vesicle deduced. The acetylcholine content of the purest preparations was considerably greater than that previously attained and reached a mean of 6.10 mmole/g of protein and 2.6 X 10(5) molecules/vesicle; the mean values, for all determinations, were 4.1 +/- S.E.M. 0.6 and 2.6 X 10(5) +/- S.E.M. 0.6 X 10(5) respectively. The lipid and protein content of the vesicle (about 140 and 80 ag/vesicle respectively) is relatively low, indicating a thin, lipid-rich membrane and a highly hydrated core of which not more than 1-2% can be occupied by protein. These findings are consistent with conclusions drawn from recent density determinations made at different osmotic pressures using penetrating and non-penetrating gradients.

[Bioassay for acetylcholine from the rat cervical sympathetic ganglion (author's transl)]

1. A bioassay for acetylcholine (Ach), with a sensitivity of 0.1 picomoles in 30 microliters (microliter) (Fig. 3), was developed using the powerful musculature of the common leech (Haemopis sanguisuga). 2. Ach was extracted from a pool of ganglia with sodium tetraphenylborate in 3-heptanone and analysed using gas chromatography. The chromatograph confirmed that the "Ach like effect" measured with bioassay was due to acetylcholine and not to one of its derivatives (Fig. 5 and 6). 3. An incubation chamber for perfusing the isolated superior cervical ganglion of the rat is described, with which it is possible to do electrophysiological experiments and to sample the Ach lost or released by the ganglion (Fig. 2). 4. Using this system, the results obtained from the resting or stimulated rat ganglion incubation in-vitro, were similar to those obtained with the cat ganglion perifused in situ. 5. Experiments were also performed to investigate the effect of removing the two precursors of Ach, glucose (Table I) and choline (Fig. 9), from the incubation medium.

Isolation, extraction, and measurement of acetylcholine from Lactobacillus plantarum

The isolation, extraction, and spectrophotometric determination of acetylcholine from Lactobacillus plantarum ATCC 10241 is described. Acetylcholine was extracted with a mixture of sodium tetraphenylboron-butylethylketone-acetonitrile and was measured enzymatically at 340 nm.

Bioanalysis of picomole amounts of acetylcholine by ion-pair partition chromatography applied to rat sciatic nerve

A method for determination of acetylcholine in small, discrete biological objects by use of ion-pair technique has been developed. Acetylcholine is extracted as an ion pair with 3,5-di-t-butyl-2-hydroxybenzenesulphonate and separated from co-extracted components by ion-pair partition chromatography with picrate as the counter ion and porous cellulose as support. The quantitative evaluation is made from the acetylcholine peak in the chromatogram obtained by ultraviolet detection. Acetylcholine has been analysed in 1 cm large pieces of rat sciatic nerve containing about 60 pmol (10 ng). The overall recovery of the method is 100 +/- 10% at the 120 pmol level of acetylcholine in a sample.

[Acetylcholine in the bovine retina and the parasympathomimetic effect of pilocarpine]

Using titrations of acetylcholine (ACh) on guinea-pig ileum the authors have demonstrated that there is no significant statistical difference between the cholinergic activity of extracts of 150 mg of retinal tissue from pilocarpinised eyes (0.3 mug of ACh) and the activity of extracts from control eyes not subjected to pilocarpine (0.29 mug of ACh). The pilocarpine had been instilled into the bovine conjunctival sac at the rate of three drops of 3 p. 100 pilocarpine HCl ten times at intervals of three minutes. One hour after the last application the animals were killed and the eyes enucleated. The role of pilocarpine in the regulation of tissues in the posterior segment of the eye is discussed.

Experimental autoimmune myasthenia gravis and myasthenia gravis: biochemical and immunochemical aspects

Stucture of acetylcholine receptor protein (AChR) purified from Electrophorus electricus (eel) by affinity chromatography is described. AChR is detected in extracts from human muscle, rat muscle, and rat thymus. Rats immunized with eel AChR develop humoral antibodies, a small fraction of which recognize AChR from rat muscle. Rats immunized with AChR exhibit myasthenia, but those immunized with denatured AChR do not. Immunoglobulin fraction of antisera to eel AChR can block the activity of AChR in electroplaques. Sera from patients with myasthenia gravis contain antibodies to AChR from human muscle detectabe at an average value 300-fold the background level in sera from nonmyasthenics. Relationship of thymoma and disease intensity to antibody titer is examined. The chronic phase of EAMG appears a good model of MG, since in both cases similar concentrations of 7-S immunoglobulin against determinants on muscle AChR other than the toxin binding site are found. Assay of anti-AChR antibody in sera from MG patients using AChR from rat muscle gives titers 10%-15% of those obtained using AChR from human muscle, and using AChR from eel gives negligible titers. The assay method described for assaying antibodies against AChR from human muscle is suggested as a diagnostic test for MG.

Choline metabolism in the cerebral cortex of guinea pigs. Stable-bound acetylcholine

1. The turnover of synaptosomal (vesicular-cytoplasmic) and stable-bound (vesicular) acetylcholine isolated from cortical tissue was investigated after the administration, under local anaesthesia, of [N-Me-(3)H]choline into the lateral ventricles of guinea pigs. 2. Radioactive acetylcholine and choline present in acid extracts of subcellular fractions were separated by a combination of liquid and column ion-exchange and thin-layer chromatography. 3. The specific radioactivity and pattern of labelling of acetylcholine present in a fraction of monodisperse synaptic vesicles was found to be essentially the same as that of synaptosomal acetylcholine. 4. The specific radioactivity of stable-bound acetylcholine present in partially disrupted synaptosomes (fraction H) at short times (10-20min) after the injection of [N-Me-(3)H]choline was very variable and inversely related to the yield of acetylcholine in that fraction. 5. Evidence was found for the existence of two small, but highly labelled pools of acetylcholine, one which could be isolated in fraction H and the other which was lost when synaptosomes, after isolation by gradient centrifugation, were left at 0 degrees C or pelleted. 6. It is concluded that the results are best explained by metabolic differences among the nerve-ending compartments (thought to be vesicles) which contain stable-bound acetylcholine. Computer simulation of our experiments supports this possibility and suggests that the highly labelled pool in fraction H is present in vesicles close to the external membrane.