Molecular Forms Of Acetylcholinesterase Research Articles

Differential inhibition of rat brain acetylcholinesterase molecular forms by 7-methoxytacrine in vitro

The effects of 7-methoxytacrine (7-MEOTA), a less toxic derivative of tetrahydroaminoacridine, on the activity of acetylcholinesterase (AChE) molecular forms were investigated in vitro. AChE molecular forms were separated by sucrose gradient sedimentation from homogenates of the frontal cerebral cortex prepared with buffer containing Triton X-100 (soluble + membrane-bound enzyme). Two molecular forms, namely 10S and 4S corresponding to globular tetrameric (G 4) and monomeric (G 1) forms, respectively, were detected; their molecular weights were 220 000 and 54 000 Da. A significantly higher sensitivity to 7-MEOTA of G 4 than of G 1 forms was observed. The K i values were 0.21 ± 0.07 μM for the former and 0.70 ± 0.15 μM for the latter. The differential inhibition of AChE molecular forms by 7-MEOTA is discussed in relation to its possible clinical application for treatment of disorders such as Alzheimer's disease, in which a reduction of brain cholinergic neurotransmission is believed to play a role.

Chronic enhancement of neuromuscular activity increases acetylcholinesterase gene expression in skeletal muscle.

We determined levels of mRNA encoding acetylcholinesterase (AChE) in muscles of rats subjected to chronic enhancement of neuromuscular activation. After 8 wk of voluntary wheel running, extensor digitorum longus (EDL) muscles displayed a 72% increase in total AChE activity as a result of a selective threefold increase in the G4 content. Soleus muscles, on the other hand, exhibited a 30% decrease in A12 while displaying a small (33%) increase in total AChE activity. These enzymatic adaptations were paralleled by increases in the levels of AChE mRNAs in both EDL (32%; P < 0.03) and soleus (42%; P < 0.02) muscles. In addition, compensatory hypertrophy of the plantaris muscle increased total AChE activity by 75%. This change was reflected by an elevation in all AChE molecular forms with A12 (89%) and A8 (179%) showing the most prominent increases. Similar to exercise-trained muscles, hypertrophied plantaris muscles displayed an increase in AChE transcripts (25%; P < 0.04). These results indicate that increases in neuromuscular activity modulate expression of the AChE gene in vivo and suggest the involvement of pretranslational regulatory mechanisms in the adaptive response of AChE to enhanced neuromuscular activation.

In Vivo Effects of Deltamethrin Exposure on Activity and Distribution of Molecular Forms of Carp AChE

The in vivo effects of the insecticide deltamethrin (DM) on the activity and molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) were examined in different organs (brain, blood serum, heart, liver, and skeletal muscle) of carp. The chosen exposure conditions were a DM concentration of 2 μg/liter in the water (12 ± 1°C) for 3 days. All the treated fish survived the experiment, though the effects of the treatment were very visible: the fish always turned on their side, and the skin/scales became infected during the exposure to DM. DM did not result in a significant change in the AChE activity in any of the studied organs except the blood plasma, where the exposure resulted in an AChE activity decrease of as much as 20%. The ratio of membrane-bound to salt-soluble AChE forms was determined in the control fish. This ratio increased in the sequence heart, skeletal muscle, liver, and brain. The distribution of the AChE molecular forms was studied in the above tissues. The brain and liver contained forms G 1, G 4, and A 12, the heart and skeletal muscle G 4, A 4, and A 12, and the blood serum G 1 and G 4. The exposure to 2 μg/liter DM for 3 days caused hardly any changes in the pattern of the different AChE molecular forms. A small, but significant ( P < 0.05) increase in the proportion of the G 4 form was observed in the liver, while G 1 and A 12 decreased by a few percent (but insignificantly). No other tissues investigated exhibited any changes in the distribution of the AChE molecular forms. The DM accumulation in the various organs was likewise examined. The DM content was lower in all tissues than the limit of detection, which was 0.002 mg/1000 g wet tissue for the brain and heart and 0.0005 mg/1000 g wet tissue for the other organs (fat, guts, kidney, liver, roe, and skeletal muscle), due to the differences in the available quantities of the different organs. This study demonstrates that DM has an effect on the distribution of the AChE molecular forms, even if its activity itself is not disturbed. However, this phenomenon is not manifested strongly at this present relatively low water temperature.

Changes Caused by Methidathion in Activity and Distribution of Molecular Forms of Carp ( Cyprinus carpio L.) AChE

The activity and molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) were characterized in the heart and skeletal muscle of carp ( Cyprinus carpio L.) exposed to 2 mg/liter of the insecticide methidathion (MD; S-2,3-dihydro-5-methoxy-2-oxo-1,3,4-thiodiazol-3-yl-methyl- O, O-dimethyl phosphodithioate) for 5 days at a water temperature of 12 ± 1°C. The specific activity of the heart AChE (4.78 ± 2.14 × 10 −2 U/mg protein) was higher than that of the muscle AChE (2.53 ± 0.75 × 10 −2 U/mg protein) in control carp. The solubility properties and molecular forms of the AChE in the two tissues were studied by extraction in high-salt medium (1 and 0.4 M NaCl) with and without Triton X-100. The ratio of membrane-bound to salt-soluble forms of AChE was higher in the muscle than in the heart. Velocity sedimentation centrifugation revealed that the skeletal muscle and the heart contained three molecular forms: G 4, A 4, and A 12. After the in vivo exposure of fish to MD, the AChE activity decreased significantly (77-92%) in the tissues investigated. Furthermore, the relative distribution of the AChE molecular forms differed somewhat from that in the control fish. Form G l became detectable after the treatment, but could not be measured in the control tissues. The proportions of the other forms decreased by a few percentages. The accumulation of MD was studied in seven organs: the brain, heart, intestine, kidney, liver, muscle, and roe. The liver and roe had the highest MD contents, and the heart and muscle had the lowest. This study shows the MD not only blocks the activity of AChE, but also modifies the distribution of its molecular forms.

Differential reactivation by HI-6 in vivo of paraoxon-inhibited rat brain acetylcholinesterase molecular forms

The effects of the cholinesterase reactivator HI-6, [1-(((4-(aminocarbonyl)-piridinio) methoxy)methyl-2-(hydroxy-imino)methyl pyridinium dichloride], on paraoxon-inhibited brain acetylcholinesterase (AChE) and its molecular forms were studied in rats. Treatment with paraoxon (0.25 mg/kg s.c.) caused approx. 60% inhibition of total AChE from frontal cerebral cortex, while that including HI-6 (140 mg/kg i.m.) and atropine (50 mg/kg i.m.) reduced such inhibition to only 25%. Two molecular forms of the enzyme, 10S and 4S, corresponding to globular tetrameric (G 4) and monomeric (G 1), were detected by sucrose gradient sedimentation. In paraoxon treated rats the G 4 form was inhibited by approx. 65% while G 1 only by 35%. The G 4 form was considerably and selectively reactivated by HI-6 while the G 1 form was not reactivated at all. The data show that HI-6 penetrates the blood-brain barrier and reactivates the molecular forms preferentially inhibited by paraoxon and involved in synaptic neurotransmission.

Sensitivity of acetylcholinesterase molecular forms to inhibition by high MgCl 2 concentration

Previous studies have shown that the asymmetric (A 12) and the dimeric (G 2), but not the tetrameric (G 4), acetylcholinesterase (AChE) forms are inactivated by high MgCl 2: concentration (Perelman and Inestrosa (1989) Anal. Biochem. 180, 227–230). Here we show that the effect of MgCl 2 on AChE activity corresponds to an irreversible inhibition and is not due to environmental effects related to the different extraction media. The anchor domain in each AChE form was not involved in the differential MgCl 2 sensitivity. Monomers derived from the various AChE forms behave in a way similar to that of the original assembled forms. Purified AChE molecular forms showed the same sensitivity to MgCl 2, than the same enzyme forms studied in tissue extracts. Neither the affinity for the substrate nor the inhibition by excess substrate of the residual AChE activity were affected by high MgCl 2. concentration. Results indicate that the differences between the tetrameric enzyme and the other two AChE molecular forms occur at the level of the catalytic subunit, probably due to differential post-translational processing.

Amphiphilic properties of molecular forms of acetylcholinesterase in normal and dystrophic muscle.

Acetylcholinesterase (AChE) molecular forms were studied in normal (NM) and in dystrophic (DM) 129B6F1/J mouse muscle. Successive extractions of the tissue with saline and saline-Triton X-100 buffers yielded two soluble fractions, S1 and S2. Forty percent of the AChE in NM was measured in S1 and 60% in S2, and 65% and 35%, respectively, in extracts from DM. A12, A8, G4, G2, and G1 forms of AChE were found in S1 and S2 from NM and DM. A similar content of asymmetric molecules was noticed between NM and DM. G4 AChE was a minor species in DM, and G1 and G2 AChE were more abundant in DM than in NM. The amphiphilic properties of the several molecules were assessed by Triton X-114 phase-partitioning and hydrophobic chromatography. Thirty and 70% of the enzyme in a mixture of S1 and S2 partitioned in the detergent-rich and in the detergent-poor phases, respectively, whether the extracts were obtained from NM or DM. Asymmetric and G4 AChE predominated in the aqueous phase and G1 and G2 in the detergent phase. Ten and 25% of the enzyme in S1 from NM or DM, respectively, was adsorbed to the phenyl-agarose. Elution of the retained enzyme followed by sedimentation analysis revealed that a certain amount of asymmetric and most of the G1 and G2 forms were associated with the matrix. The content of amphiphilic asymmetric and light globular forms was notably higher in DM than in NM. The results suggest that dystrophic muscle produces a specific pattern of molecular forms of AChE.

Investigation of Effects of Pesticides on Molecular Forms of AChE in Alimentary Canals of Carp

All parts of the carp intestine contain three different molecular forms of acetylcholinesterase (AChE): G1, G4 and A12. After paraquat treatment there were no significant changes in AChE activity, whereas after CuSO4 treatment there was a slight increase in activity. During exposure of carp to 2 ppm methidathion in vivo, the AChE activity in the tissues investigated decreased significantly. Moreover, the relative distribution of the molecular forms of AChE changed relative to that in the control animals. The results suggest that an investigation of the molecular forms of fish AChE could contribute to an understanding of fish AChE at a molecular level and emphasize the importance of in vivo and in vitro approaches in assessing chemical effects and their potential hazards in the aquatic environment.

Excitotoxicity and cholinergic chemical markers during programmed motor neurone death

We measured cholinergic markers and acetylcholinesterase (AChE) molecular forms after glutamate receptor stimulation of superfused slices of mouse spinal cord at different developmental ages. AChE globular forms were secreted in a dose-dependent fashion. A period of selective sensitivity to excitotoxic agents was detected by increased acetylcholine (ACh) release and AChE secretion (sAChE) at postnatal day 14. Strychnine-resistant glycine stimulation potentiated glutamate-induced AChE release, suggesting N- methyl- d-aspartate (NMDA) receptor involvement.

Evolution of Acetylcholinesterase Transcripts and Molecular Forms During Development in the Central Nervous System of the Quail

We studied the expression of acetylcholinesterase (AChE) in the nervous system (cerebellum, optic lobes and neuroretina) of the quail at different stages of development, from embryonic day 10 (E10) to the adult. Analyzing AChE mRNAs and AChE molecular forms, we observed variations in the following: (a) production of multiple mRNA species (4.5 kb, 5.3 kb, and 6 kb); (b) translation and/or stability of the AChE protein; (c) production of active and inactive AChE molecules; (d) production of amphiphilic and nonamphiphilic AChE forms; and (e) proportions of tetrameric G4, dimeric G2, and monomeric G1 forms. The large transcripts present distinct temporal patterns and disappear in the adult, which possesses only the 4.5-kb mRNA; these changes are unlikely to be related to those observed for the AChE protein, because all transcripts seem to encode the same catalytic subunit (type T). In addition, the levels of mRNA and AChE are not correlated in the three regions, especially at the adult stage. The proportion of inactive AChE was found to be markedly higher at the hatching period (E16) than at earlier stages (E10 and E13) or in the adult. The G4 form is predominant already at E10, and in the adult its proportion reaches 80% of the activity in the cerebellum and optic lobes, and 65-70% in the neuroretina. This form is largely nonamphiphilic in embryonic tissues, but it becomes progressively more amphiphilic with development. Thus, the different processing and maturation steps appear to be regulated in an independent manner and potentially correspond to physiologically adaptative mechanisms.

The functional role of molecular forms of acetylcholinesterase in neuromuscular transmission.

The severity of poisoning following acetylcholinesterase (AChE) inhibition correlates weakly with total AChE activity. This may be partly due to the existence of functional and non-functional pools of AChE. AChE consists of several molecular forms. The aim of the present study was to investigate which of these forms will correlate best with neuromuscular transmission (NMT) remaining after partial inhibition of this enzyme. Following sublethal intoxication of rats with the irreversible AChE inhibitor soman, diaphragms were isolated after 0.5 or 3 h. It appeared that at 3 h after soman poisoning the percentage of G1 increased, while those of G4 and A12 decreased. NMT was inhibited more strongly than in preparations obtained from the 0.5 h rats with the same level of AChE inhibition, but with a normal ratio of molecular forms. NMT correlated positively with G4 as well as with A12, but inversely with G1. In vitro inhibition with the charged inhibitors DEMP and echothiophate resulted in higher levels of total AChE, relatively less G1 and more G4 and A12 than after incubation with soman, but led to less NMT. Treatment of soman-intoxicated rats with the reactivating compound HI-6 resulted in preferential reactivation of A12, persisting low levels of G1 and concurrent recovery of NMT as compared with saline-treated soman controls with equal total AChE activity. Apparently, in rat diaphragm G4 and A12 are the functional AChE forms.

Acetylcholinesterase adaptation to voluntary wheel running is proportional to the volume of activity in fast, but not slow, rat hindlimb muscles.

Chronic enhancement of neuromuscular activity by forced exercise training programmes results in selective adaptation of the G4 acetylcholinesterase (AChE) molecular form in hindlimb fast muscles of the rat, with only minor and non-selective AChE changes in the soleus. In order to shed further light on the physiological significance of this G4 adaptation to training, we turned to a voluntary exercise model. The impact of 5 days and 4 weeks of voluntary wheel cage running on AChE molecular forms was examined in four hindlimb fast muscles and the slow-twitch soleus from two rat strains. Inbred Fisher and Sprague-Dawley rats, placed in live-in wheel cages, exercised spontaneously for distances which progressively increased up to an average of approximately 3 and 18 km/day, respectively, by the end of week 4. Fast muscles responded to this voluntary activity by massive G4 increases (up to 420%) with almost no changes in A12, so that by week 4 the tetramer became the main AChE component of these muscles. The additional G4 was composed primarily of amphiphilic molecules, suggesting a membrane-bound state. The G4 content of fast muscles was highly correlated with the distance covered by the rats during the 5 days before they were killed (r = 0.850-0.879, P < 0.001 in three muscles). The soleus muscle, in turn, responded to wheel cage activity by a marked selective reduction of its asymmetric forms--up to 45% for A12. This A12 decline, already maximal by day 5 of wheel cage running, showed no relationship with the distance covered.(ABSTRACT TRUNCATED AT 250 WORDS)

Satellite cells in slow and fast rat muscles differ in respect to acetylcholinesterase regulation mechanisms they convey to their descendant myofibers during regeneration

The hypothesis of satellite cell diversity in slow and fast mammalian muscles was tested by examining acetylcholinesterase (AChE) regulation in muscles regenerating 1) under conditions of muscle disuse (tenotomy, leg immobilization) in which the pattern of neural stimulation is changed, and 2) after cross-transplantation when the regenerating muscle develops under a foreign neural stimulation pattern. Soleus (SOL) and extensor digitorum longus (EDL) muscles of the rat were allowed to regenerate after ischemic-toxic injury either in their own sites or had been cross-transplanted to the site of the other muscle. Molecular forms of AChE in regenerating muscles were analyzed by velocity sedimentation in linear sucrose gradients. Neither tenotomy nor limb immobilization significantly affected the characteristic pattern of AChE molecular forms in regenerating SOL muscles, suggesting that the neural stimulation pattern is probably not decisive for its induction. During an early phase of regeneration, the general pattern of AChE molecular forms in the cross-transplanted regenerating muscle was predominantly determined by the type of its muscle of origin, and much less by the innervating nerve which exerted only a modest modifying effect. However, alkali-resistant myofibrillar ATPase activity on which the separation of muscle fibers into type I and type II is based, was determined predominantly by the motor nerve innervating the regenerating muscle. Mature regenerated EDL muscles (13 weeks after injury) which had been innervated by the SOL nerve became virtually indistinguishable from the SOL muscles in regard to their pattern of AChE molecular forms. However, AChE patterns of mature regenerated SOL muscles that had been innervated by the EDL nerve still displayed some features of the SOL pattern. In regard to AChE regulation, muscle satellite cells from slow or fast rat muscles convey to their descendant myotubes the information shifting their initial development in the direction of either slow or fast muscle, respectively. The satellite cells in fast or slow muscles are, therefore, intrinsically different. Intrinsic information is expressed mostly during an early phase of regeneration whereas later on the regulatory influence of the motor nerve more or less predominates.

Chromodacryorrhea in Rats: Absence Following Soman Poisoning

Chromodacryorrhea is the secretion of so-called "bloody tears" from the harderian gland which nearly circumscribes the eye within the bony orbit. Direct-acting cholinergic agonists such as oxotremorine, carbachol, and pilocarpine caused chromodacryorrhea but nicotine did not. Atropine blocked chromodacryorrhea induced by systemic administration of direct-acting cholinergic agonists. Thus, chromodacryorrhea appears to be a muscarinic receptor-related event. Soman (pinacolyl methylphosphonofluoridate), a potent irreversible inhibitor of acetylcholinesterase which increases the synaptic concentration of the neurotransmitter acetylcholine, did not induce chromodacryorrhea in rats. Similarly, physostigmine, a tertiary, carbamate acetylcholinesterase inhibitor, did not induce chromodacryorrhea. In vivo soman-induced inhibition of harderian gland acetylcholinesterase was independent of the soman dose and the inhibition was significantly less than brain acetylcholinesterase. In vitro soman-induced inhibition of harderian gland acetylcholinesterase was not significantly different from that of diaphragm acetylcholinesterase. The lack of inhibition of acetylcholinesterase in the harderian gland does not appear to be due to a difference in sensitivity to inhibition by soman. The distribution of the various molecular forms of acetylcholinesterase between the diaphragm and harderian gland was different. There was a great deal more of the 4S form of acetylcholinesterase in the harderian gland than in the diaphragm. The lack of the following, inhibition of harderian gland acetylcholinesterase and elevation of the synaptic concentration of acetylcholine, could explain the absence of chromodacryorrhea following soman poisoning. The discrepancy between the significant soman induced inhibition of brain acetylcholinesterase and the lack of inhibition of harderian gland acetylcholinesterase allows one to speculate that there may be a very efficient scavenger of soman present in the rat harderian gland.

Reduced levels of globular and asymmetric forms of acetylcholinesterase in rat left ventricle with pressure overload hypertrophy

The aim of the present work was to determine the effect of abdominal aortic stenosis on molecular forms of acetylcholinesterase (AChE) in rat heart. Pressure-overload, left ventricular hypertrophy was produced in male Sprague-Dawley rats by suprarenal abdominal aortic constriction. After two weeks the relative heart weight was increased over 20% compared to sham-surgical controls, mostly due to left ventricular enlargement. Aortic constriction reduced AChE activity per wet weight and per unit protein by 25–30% in the left ventricle and interventricular septum, but not in the other chambers. However, total AChE activity per chamber was normal in the left ventricle and interventricular septum, but was elevated in the atria. The molecular forms of AChE were separated in linear sucrose gradients and their specific activities were calculated from the resulting percent activities and total AChE activities. This data showed that although aortic constriction had no effect on ratios of the various forms, it did reduce the specific activities of globular and asymmetric forms in the left ventricle and interventricular septum. The reduced AChE activity suggests that slower rates of ACh hydrolysis occur in the left ventricle in pressure-overload hypertrophy.

Continuous low amplitude direct current stimulation of the crushed peripheral nerve accelerates the early recovery of choline acetyltransferase but not of acetylcholinesterase activity in fast and slow muscles

We investigated if continuous 1 µA direct current stimulation of the injured nerve, with the cathode electrode at the distal end of the nerve crush injury (cathode stimulation), accelerated the recovery of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity in transiently denervated extensor digitorum longus (EDL) and soleus (SOL) rat muscles. ChAT is a specific marker of cholinergic nerve terminals and may reflect axon ingrowth, and AChE reflects the re-establishment of neuromuscular junctions and recovery of muscle activity. Compared to sham operated animals, the cathode (CA) stimulated rats had a statistically significant larger ChAT activity in the EDL and SOL muscles on days 12 and 14 after nerve crush (P < 0.01, n = 6). The difference in ChAT activity between the groups decreased thereafter. Regarding recovery of muscle AChE, CA stimulation of the crushed sciatic nerve did not detectably accelerate the normalization of activity and pattern of AChE molecular forms in the EDL and SOL muscles. This means that the early rise in ChAT muscle activity in CA stimulated rats was not followed by an accelerated normalization of the neuromuscular transmission in the same group. It is more likely that the higher ChAT activity observed after cathode stimulation indicates a higher ChAT content in regenerating motor nerve endings, rather than a greater number of motor axons entering the muscles. It seems possible that cathode stimulation increased ChAT axonal transport, causing the early increase of ChAT content in the nerve endings. This raises the possibility that the axon transport and subsequent secretion of a trophic factor(s) from the nerve to the reinnervated muscle are enhanced as well, thus shortening the overall time of muscle force recovery in the absence of an appreciable acceleration of recovery of the neuromuscular transmission.

Calcium influxes and calmodulin modulate the expression and physicochemical properties of acetylcholinesterase molecular forms during development in vivo.

1. Acetylcholinesterase (AcChoE; EC 3.1.1.7) exists in several molecular forms that may be anchored to cell membranes or associated with extracellular matrix. AcChoE bound to lipidic membranes is detergent extractable (DE AcChoE), whereas the enzyme associated with extracellular matrix is high salt soluble (HSS AcChoE). The latter variant is accumulated in synaptic regions by an unknown mechanism. 2. We have suggested previously that depolarization-induced Ca2+ influx is a major factor that modulates AcChoE synthesis in vivo, as well as the conversion of some DE AcChoE to HSS variant. In the present study, we have examined (i) the effects of depolarization-induced skeletal muscle inactivity and ionophore-induced Ca2+ influxes on the expression of AcChoE molecular forms and (ii) the hypothesis that Ca(2+)-dependent calmodulin may be involved in the conversion of at least some forms of DE AcChoE to HSS variant in vivo. 3. Chick embryos were treated in ovo during the early period of nerve-muscle interactions with d-tubocurarine (dTC; a competitive neuromuscular blocking agent) or with decamethonium (dMET; a depolarizing agent). Both dTC and dMET equally and significantly reduced embryonic neuromuscular activity (motility). However, dTC significantly decreased AcChoE overall activity, whereas dMET had virtually no effect on AcChoE expression, compared to controls. 4. Treatment of embryos with the Ca2+ ionophore A23187 significantly increased the total AcChoE activity as well as the DE/HSS ratio of each AcChoE molecular form. However, treatment with N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide (also termed W-7), a calmodulin antagonist, did not alter the total AcChoE activity, but significantly increased the DE/HSS ratio of AcChoE forms. 5. These results support the idea that (i) depolarization and/or Ca2+ influxes, but not muscle contraction, may regulate AcChoE expression in skeletal muscle and (ii) Ca(2+)-dependent calmodulin activation may be involved in the conversion of some DE AcChoE to their HSS variant in vivo.

Molecular forms of acetylcholinesterase in microsomal membranes of normal and dystrophic muscle

Molecular forms of acetylcholinesterase in microsomal membranes of normal and dystrophic muscle

Acetylcholine levels, choline acetyltransferase and acetylcholinesterase molecular forms during thyroxine-induced cardiac hypertrophy

The effects of left ventricular hypertrophy induced by hyperthyroidism on three biochemical markers of parasympathetic innervation were investigated. In response to subcutaneous injections of thyroxine (400 μg/kg: T 4) for 6 days, the left ventricle, but not the right, developed significant hypertrophy (20%). In the enlarged left ventricle, acetylcholine (ACh) content and choline acetyltransferase (ChAT) activity per chamber were elevated approx. 25–30%, although no change in these two markers was evident when the data were expressed per unit wet weight. Immunoblot analysis showed that the relative abundance of ChAT protein increased in the hypertrophied left ventricle in correlation with the increased ChAT activity. No changes in ACh content, ChAT activity and ChAT relative abundance were evident in the right ventricle of T 1-treated animals. Although hyperthyroidism did not alter AChE specific activity (per unit wet weight) in the left ventricle, the percent activities of the individual AChE globular forms were affected in this chamber. Specifically, T 4-treatment reduced the percent activity of globular (G) 4 AChE by 20% and increased that of the combined G 1 and G 2 AChE pool by 15%. Interestingly, in the hypertrophied left ventricle total AChE activity in its extracellular or functionally-relevant pool was reduced due to a loss of G 4 AChE activity. These results show that a compensatory increase in parasympathetic innervation can occur during hyperthyroid-induced left ventricular hypertrophy. However, the reduced activity of the functionally-relevant AChE pool suggests that the clearance of ACh after release may be slowed in the hypertrophied left ventricle.

Influence of denervation on the molecular forms of junctional and extrajunctional acetylcholinesterase in fast and slow muscles of the rat.

Acetylcholinesterase (AChE) molecular forms in denervated rat muscles, as revealed by velocity sedimentation in sucrose gradients, were examined from three aspects: possible differences between fast and slow muscles, response of junctional vs extrajunctional AChE, and early vs late effects of denervation. In the junctional region, the response of the asymmetric AChE forms to denervation is similar in fast extensor digitorum longus (EDL) and slow soleus (SOL) muscle: (a) specific activity of the A12 form decreases rapidly but some persists throughout and even increases after a few weeks; (b) an early and transient increase of the A4 AChE form lasting for a few weeks may be due to a block in the synthetic process of the A12 form. In the extrajunctional regions, major differences with regard to AChE regulation exist already between the normal EDL and SOL muscle. The extrajunctional asymmetric AChE forms are absent in the EDL because they became completely repressed during the first month after birth, but they persist in the SOL. Differences remain also after denervation and are, therefore, not directly due to different neural stimulation patterns in both muscles: (a) an early but transient increase of the G4 AChE occurs in the denervated EDL but not in the SOL; (b) no significant extrajunctional activity of the asymmetric AChE forms reappears in the EDL up till 7 wk after denervation. In the SOL, activity of the asymmetric AChE forms is decreased early after denervation but increases thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)