Molecular species of acetylcholinesterase in denervated rat skeletal muscle

Effect of thyroid hormones on acetylcholinesterase mRNA levels in the slow soleus and fast extensor digitorum longus muscles of the rat

In the rat, the level of acetylcholinesterase messenger RNA in the typical slow soleus muscles is only about 20-30% of that in the fast extensor digitorum longus muscles. The expression of contractile proteins in muscles is influenced by thyroid hormones and hyperthyroidism makes the slow soleus muscle faster. The influence of thyroid hormones on the levels of acetylcholinesterase messenger RNA level in the slow soleus and fast extensor digitorum longus muscle of the rat was studied in order to examine the effect of thyroid hormones on muscle acetylcholinesterase expression. Hyperthyroidism was induced in rats by daily thyroid hormone injection or thyroid hormone releasing tablet implantation. Hind-limb suspension was applied to produce muscle unloading. Muscle denervation or reinnervation was achieved by sciatic nerve transection or crush. Acetylcholinesterase messenger RNA levels were analyzed by Northern blots and evaluated densitometrically. Hyperthyroidism increased the levels of acetylcholinesterase messenger RNA in the slow soleus muscles close to the levels in the fast extensor digitorum longus. The effect was the same in the unloaded soleus muscles. Acetylcholinesterase expression increased also in the absence of innervation (denervation), in the presence of changed nerve activation pattern (reinnervation), and under enhanced tonic neural activation of the soleus muscle (electrical stimulation). However, the changes were substantially smaller than those observed in the control soleus muscles. Enhancement of acetylcholinesterase expression in the soleus muscles by the thyroid hormones is, therefore, at last in part due to hormonal effect on the muscle itself. On the contrary, increased level of the thyroid hormones had no influence on acetylcholinesterase expression in the normal fast extensor digitorum longus muscles. However, some enhancing influence was apparent whenever the total number of nerve-induced muscle activations per day in the extensor digitorum longus muscle was increased. Thyroid hormones seem to be an independent extrinsic factor of acetylcholinesterase regulation in the slow soleus muscle.

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)

Acetylcholinesterase is orientated facing the cytoplasmic side in membranes derived from sarcoplasmic reticulum

(1) Microsomal membranes from white rabbit muscle enriched in sarcoplasmic reticulum (SR) were used to investigate the preferential localization of acetylcholinesterase (AChE) in these membranes. (2) Integrity and orientation of the vesicles was assessed by measuring the inulin-inaccessible space of the vesicles and its calcium-loading capacity. (3) Treatment of the membranes with diisopropyl phosphorofluoridate (DFP), an irreversible inhibitor which is free soluble in lipid, produced an almost complete inactivation of AChE. The inhibition was prevented in assays performed with the non-permeant reversible inhibitor BW 284c51 (BW). (4) Similar results were obtained if echothiophate iodide (ECHO), an irreversible and poorly permeant inhibitor, instead of DFP was used. (5) Sedimentation profiles of enzyme solubilized with Triton X-100 from membranes inhibited by DFP after protection with BW showed a minor reduction in the relative proportion of a 4.5 S (G1) form. (6) Treatment of intact or saponin-permeabilized membranes with concanavalin A (ConA) produced enzyme-lectin complexes. In both cases, most of the enzyme was recovered in the sedimented complexes after centrifugation of the Triton-solubilized membranes. (7) Incubation of intact membranes with the antibody AE1 led to the formation of immuno complexes. Sedimentation analyses of the molecular forms of AChE revealed a shift in the sedimentation coefficients, whether the antibody was added before or after solubilization of the enzyme. (8) These results firmly establish an external localization of AChE in SR, most of the protein backbone facing the cytoplasmic side of the membrane.

Differential effects of denervation on acetylcholinesterase activity in parasympathetic and sympathetic ganglia of the frog, Rana pipiens

The transsynaptic regulation of acetylcholinesterase (AChE) was studied by recording the changes in enzymatic activity following denervation in two types of autonomic ganglia in the frog, Rana pipiens. Opposite effects on AChE were found in the parasympathetic cardiac ganglion and in the sympathetic lumbar ganglion; denervation produced a significant increase in AChE activity in cardiac ganglia but a significant decrease in lumbar ganglia. The relative effects of denervation on intracellular and total AChE were examined by selectively inhibiting extracellular AChE with echothiophate, a poorly lipid-soluble cholinesterase inhibitor. Denervation resulted in a significant increase in intracellular AChE in cholinergic cardiac ganglia but had no effect on intracellular AChE activity in adrenergic lumbar ganglia. Histochemical studies revealed little change in extracellular AChE staining upon denervation in the cardiac ganglion, whereas in the lumbar ganglia there was a loss of AChE-specific reaction product. These results raise the possibility that the transsynaptic control of AChE activity by innervation in the frog is influenced by the transmitter synthetic properties of the postsynaptic ganglion cells.

Denervation-induced alterations of acetylcholinesterase in denervated and nondenervated muscle

The influence of denervation on acetylcholinesterase (AchE) molecular forms in rat skeletal muscle for durations up to 30 days is examined in denervated anterior tibialis, the innervated contralateral muscle, and diaphragm. Denervated rats at a common age of 8.5 weeks are compared with age-matched, nondenervated animals. The results indicate that time-dependent losses of AchE in denervated muscle occur more rapidly than loss of muscle mass and are not uniform among the different molecular forms. Loss of the 4 S and 16 S forms is rapid and essentially complete within 3.5 days of denervation, while during this same period the 10.5 S form undergoes a transient twofold increase and its presence in denervated muscle is never abolished. Within 30 days of denervation, all forms of AchE including the 16 S species reappear. A salient finding of these studies is that the effects of denervation are evident also in anatomically remote, innervated muscle such as anterior tibialis of the contralateral limb and in diaphragm. These alterations appear as pronounced reductions in 4 S AchE and increases in 10.5 S AchE; the asymmetric collagen-tailed 16 S form is unaltered. Treatment of primary cultures of embryonic chick pectoral muscle with sera from denervated but not nondenervated rat causes reductions in AchE. These results indicate that the appearance and retention of AchE, in particular the 16 S form, occur in the absence of functional innervation. The effects of denervation on AchE metabolism in remote, innervated tissue are consistent with the action of a diffusible factor released from severed nerve or muscle, or both.

Selective increase of tetrameric (G4) acetylcholinesterase activity in rat hindlimb skeletal muscle following short-term denervation

Acetylcholinesterase (AChE; EC 3.1.1.7) isoenzymes in gracilis muscles from adult Sprague-Dawley rats were studied 24-96 h after obturator nerve transection. Results show a selective denervation-induced increase in the globular G4 isoform, which is predominantly associated with the plasmalemma. This enzymatic increase was (a) transient (occurring between 24 and 60 h) and accompanied by declines in all other identifiable AChE isoforms; (b) observed after concurrent denervation and inactivation of the enzyme with diisopropylfluorophosphate, but not following treatment with cycloheximide; and (c) more prominent in the extracellular compartment of muscle endplate regions. Aside from this transient change, G4 activity did not fall below control levels, indicating that at least the short-term maintenance of G4 AChE (i.e., at both normal and temporarily elevated levels) does not critically depend on the presence of the motor nerve. In addition, this isoform's activity increases in response to perturbations of the neuromuscular system that are known to produce elevated levels of acetylcholine (ACh), such as short-term denervation and exercise-induced enhancement of motor activity. The present study is consistent with the hypothesis that individual AChE isoforms in gracilis muscle are subject to distinct modes of neural regulation and suggests a role for ACh in modulating the activity of G4 AChE at the motor endplate.

Axonal transport in mdx mouse sciatic nerve

Anterograde and retrograde flows of acetylcholinesterase (AChE) in sciatic nerves of adult mdx mice were compared with those of normal mice. Specific molecular forms of AChE were resolved by high-performance liquid chromatography such that slow anterograde (G1 + G2), fast anterograde and fast retrograde (G4 and A12) flows could be simultaneously studied. Although we found no difference in the total AChE activity and the molecular forms in non-ligated nerves between mdx and the normal mice, ligated nerves showed significant differences. The total AChE activity accumulated at the proximal segment of ligated nerve was higher in mdx mice than in normal mice after 24 h ligation. The G1 + G2 molecular forms were accumulated more in the proximal segment of mdx than the normal. A12, on the other hand, was more abundant in both segments of mdx mice than the normal. No statistically significant difference in the accumulated amount of G4 molecular form was present between mdx and the normal mice at either proximal or distal segment. These results indicated that axonal flow in sciatic nerve likely plays a role in muscle regeneration, and that the transport machinery in dystrophin-deficient mdx neuron is probably normal.

Serum cholinesterase activity in infantile and juvenile spinal muscular atrophy

Serum acetylcholinesterase (AChE) and pseudocholinesterase (ChE) activity in infantile and juvenile spinal muscular atrophy (SMA) was determined. The total AChE activity was either normal or decreased in the childhood SMA (Type 1), the other SMA groups and disease controls (ALS, X-linked SMA). In the majority of SMA Type 1 cases (6/7 tested) an absence of the asymmetric A12 form was found. This was accompanied by changes in the other asymmetric and globular forms. The latter was, however, not specific for SMA Type 1 cases. The ChE activity was increased in the majority of SMA cases as well as disease controls. The asymmetric A12 ChE form was increased in all SMA Type 3 cases, the values of this form in SMA Type 1 was variable. A change in the ChE globular forms in SMA Type 1 and SMA Type 2 was a frequent finding. It is suggested that the absence of the asymmetric A12 AChE form in SMA Type 1 arises because of muscle cell immaturity and undeveloped muscle-nerve interactions. The reason of ChE changes is obscure.

Posthatching changes in levels and molecular forms of acetylcholinesterase in slow and fast muscles of the chicken: effects of denervation and direct electrical stimulation

The evolution of acetylcholinesterase (AChE) activity and AChE molecular form distribution were studied in slow-tonic anterior latissimus dorsi (ALD) and in fast-twitch posterior latissimus dorsi (PLD) muscles of chickens 2-18 days of age. In ALD as well as in PLD muscles, the AChE-specific activity increased transiently from day 2 to day 4; the activity then decreased more rapidly in PLD muscle. During this period asymmetric AChE forms decreased dramatically in ALD muscle and the globular forms increased. In PLD muscle, the most striking change was the decline in A8 form between days 2 and 18 of development. Denervation performed at day 2 delayed the normal decrease in AChE-specific activity in PLD muscle, whereas little change was observed in ALD muscle. Moreover, A forms in these two muscles were virtually absent 8 days after denervation. Direct electrical stimulation depressed the rise in AChE-specific activity in denervated PLD muscle and prevented the loss of the A forms. Furthermore, the different molecular forms varied according to the stimulus pattern. In ALD muscle, electrical stimulation failed to prevent the effect of denervation. This study emphasizes the differential response of denervated slow and fast muscles to electrical stimulation and stresses the importance of the frequency of stimulation in the regulation of AChE molecular forms in PLD muscle during development.

2,4-Dichlorophenoxyacetic acid (2,4-D) reduces acetylcholinesterase activity in rat muscle

A single dose (200 mg/kg body weight, i.p.) of 2,4-dichlorophenoxyacetic acid (2,4-D), commonly used as a herbicide, caused significant decreases in acetylcholinesterase (AChE) activity in diaphragm and other muscles of the rat. The 4S, 10S, and 16S forms of AChE were affected. The effect was maximal 15 to 24 h after injection. Choline acetyltransferase (CAT) activity was not affected. Neither AChE nor CAT activities changed in sciatic nerve from 2,4-D-treated animals. Spontaneous locomotor activity decreased dramatically 4 h after 2,4-D treatment. Myotonia that was present 1.5 h after 2,4-D injection became maximal at 2 to 6 h. Twenty-four hours after drug injection, when animals were recovering from myotonia, spontaneous locomotor activity was still depressed to 50% of control values. Prolonged distal motor latencies were observed 15 to 24 h after drug administration. AChE activity and spontaneous locomotor activity returned to control values at 48 h. Thus, 2,4-D causes a decrement of end-plate AChE, as well as behavioral and electrophysiologic changes. Decreased activity of AChE may be an early step in development of the myopathy that occurs after large dose 2,4-D.

Asymmetric molecular forms of acetylcholinesterase in mammalian skeletal muscles

Velocity sedimentation analysis of acetylcholinesterase (AChE) molecular forms was performed separately in endplate-rich and endplate-free regions of the diaphragm muscle of the rat, guinea pig, rabbit, dog, and pig, and in mm. erectores trunci and m. vastus lateralis in man. Several high-ionic-strength media were first tested to achieve better solubilization of AChE from rat muscles than by the usual 1 M NaCl-Triton X-100 medium. Ninety-five percent of the AChE from the motor endplate region of the rat diaphragm was solubilized in a single extraction step by medium containing 1 M lithium chloride instead of NaCl. Homologous molecular forms of AChE were found in all species. The asymmetric forms were invariably present in the endplate regions of muscles but their activity in endplate-free regions was much lower than in endplate regions in all investigated mammals except in man. Essentially the same pattern of AChE molecular forms was present in both regions in human muscles. High extrajunctional activity of the asymmetric forms makes human muscles similar to immature rodent muscles in vivo and in culture. The pattern of AChE molecular forms in the endplate region of the diaphragm in senile 24-month-old rats was not significantly different from that in 3-month-old animals. The persistence of the asymmetric AChE forms in the diaphragm of senile rats suggests that neuromuscular interactions do not become deficient with age in this muscle.

Endplate topography of denervated and disused rat neuromuscular junctions: comparison by scanning and light microscopy

The effect of denervation and tetrodotoxin-induced muscle disuse on endplate structure was investigated in rat hind-limb muscles. The endplate was visualized by light microscopic cholinesterase staining and by scanning electron microscopy. Denervation resulted in a reduction in histochemically determined endplate dimensions proportionate to the decrease in muscle fiber circumference. Scanning electron microscopy, on the other hand, revealed a flattening or more often collapse of primary grooves with a reduction in the width of the endplate but no longitudinal shrinkage. Primary groove area per se was not measurable due to the loss of primary groove structural integrity. Thus, the apparent histochemical diminution of endplate length after denervation was artefactual, probably due to loss of cholinesterase activity and impeded access of substrate. In disuse, cholinesterase staining revealed a similar reduction in endplate girth with fiber atrophy but with a corresponding increase in endplate length. Scanning electron microscopy of disused muscle fibers confirmed these histochemical findings and the overall preservation of primary groove area. Disuse also resulted in an increase in the number of intrasynaptic primary groove branches as visualized by scanning electron microscopy. Finally, a specialized endplate "raised area", prominent in soleus muscle, was greatly reduced after disuse but much less so after denervation. Thus, after denervation, primary groove structural integrity is lost and the shape of the endplate passively follows that dictated by circumferential loss of surface membrane. In disused muscle, presence of an intact axon preserves the structure and area but not the orientation of the primary grooves which are distorted by fiber atrophy. Disuse also strongly affects other endplate surface structures visualized by scanning electron microscopy.

Characterization of acetylcholinesterase molecular forms in slow and fast muscle of rat

Multiple molecular forms of acetylcholinesterase (AChE EC 3.1.1.7) from fast and slow muscle of rat were examined by velocity sedimentation. The fast extensor digitorum longus muscle (EDL) hydrolyzed acetylcholine at a rate of 110 mumol/g wet weight/hr and possessed three molecular forms with apparent sedimentation coefficients of 4S, 10S, and 16S which contribute about 50, 35, and 15% of the AChE activity. The slow soleus muscle hydrolyzed acetylcholine at a rate of 55 mumol/g wet weight/hr and has a 4S, 10S, 12S, and 16S form which contribute 22, 18, 34, and 26% of AChE activity, respectively. A single band of AChE activity was observed when a 1M NaCl extract with CsCl (0.38 g/ml) was centrifuged to equilibrium. Peak AChE activity from EDL and SOL extracts were found at 1.29 g/ml. Resedimentation of peak activity from CsCl gradients resulted in all molecular forms previously found in both muscles. Addition of a protease inhibitor phenylmethylsulfonyl chloride did not change the pattern of distribution. The 4S form of both muscles was extracted with low ionic strength buffer while the 10S, 12S, and 16S forms required high ionic strength and detergent for efficient solubilization. All molecular forms of both muscles have an apparent Km of 2 x 10(-4) M, showed substrate inhibition, and were inhibited by BW284C51, a specific inhibitor of AChE. The difference between these muscles in regards to their AChE activity, as well as in the proportional distribution of molecular forms, may be correlated with sites of localization and differences in the contractile activity of these muscles.

Nerve crush induced changes in molecular forms of acetylcholinesterase in soleus and extensor digitorum muscles

The molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) extracted from the fast twitch extensor digitorum longus (EDL) and slow twitch soleus (SOL) muscles, were separated by velocity sedimentation after sciatic nerve crush. Three molecular forms were routinely separated from EDL and four from SOL muscle. In the EDL, the 4S and 10S represented the greatest amounts of AChE, and in the SOL the 12S and 16S were the major constituent forms of the enzyme. Total AChE activity in EDL and SOL muscles rapidly decreased after nerve crush. During reinnervation (2 weeks postcrush), total AChE activity in the EDL gradually recovered, whereas the SOL exhibited a 2.5-fold transient increase above control. Immediately after denervation, decreases in the three AChE forms from the EDL (4, 10, and 16S) were evident, whereas the SOL exhibited both rapid increases (4 and 10S) and decreases (12S and 16S). In both muscles the 4S form reappeared before the 16S and 10S molecular forms, suggesting that the light form, 4S, may be a precursor of the heavier molecules. Transient increases during reinnervation occurred in the 16S AChE form in both muscles; however, they were approximately five times greater in the SOL than in the EDL. In the SOL all other molecular forms showed similar increases, whereas none was seen in the EDL. Possible mechanisms are differences in synthesis and catabolism, and in release of molecular forms from these muscles.

Exercise effects on recovery of muscle acetylcholinesterase from reduced neuromuscular activity

In order to investigate the effects of reduced and subsequently increased neuromuscular activity on muscle acetylcholinesterase (AChE), rats had one hindlimb immobilized with plaster casts for 4 weeks and were killed either at the end of immobilization (group I), after 4 weeks of resumed normal activity following cast removal (group R), or after 4 weeks of resumed activity supplemented with a daily treadmill-walking task (group E). Immobilization resulted in a decrease in adductor longus muscle weight to 66.4% of control; total muscle end-plate-associated AChE was decreased to 51.4%. Total muscle ACh hydrolysis was not significantly affected. Mild daily exercise during recovery increased total muscle end-plate AChE to control levels after 4 weeks, while in group R the corresponding level was significantly lower (84.4%). Decreased neuromuscular activity has different effects on end-plate AChE and non-end-plate AChE. Mild endurance-type overload during recovery from immobilization can accelerate recovery of end-plate AChE activity to normal.

Acetylcholinesterase aggregates in a newly formed motor nerve-smooth muscle junction

We have studied the changes in acetylcholinesterase (AChE) molecular forms during cross-innervation of the inferior smooth muscle of the cat nictitating membrane by the hypoglossal nerve. One month after functional cross-innervation AChE activity increases by two-fold above control values, and a new high molecular weight AChE form (A12) is detected, BW284c51, an anti-AChE, potentiates the contraction of the cross-innervated smooth muscle. Three months later, AChE activity has raised six-fold above normal values. At this time, half of the activity sediments to the bottom of the sucrose gradient and a time-dependent dissociation occurs in lighter AchE forms, reminiscent of AChE aggregates observed in the electric eel. We discuss the possibility that the multimolecular aggregates are involved in the immobilizatin of AChE at the neuromuscular junction of a motor nerve and a smooth muscle.

Effects of acute and chronic denervation on release of acetylcholinesterase and its molecular forms in rat diaphragms

Hemidiaphragms were removed from rats at various times after intrathoracic transection of the left phrenic nerve and were incubated in organ baths containing 1.5 ml of oxygenated, buffered physiologic saline solution, with added glucose and bovine serum albumin. After incubation, the acetylcholinesterase (AChE: EC 3.1.1.7) activities of the bath fluid and of the muscle were determined. Innervated left hemidiaphragms were found to release 107 units of AChE over a 3-h period, corresponding to 1.9% of their total AChE activity. Denervation led to a rapid loss of AChE from the muscle coincident with a transient increase in the outpouring of enzyme activity into the bath fluid. Thus, 1 day after nerve transection the left hemidiaphragm contained only 68% of the control amounts of AChE activity, but released 140% as much as control. After 3 or 4 days of denervation, the AChE activity of the diaphragm stabilized at 35% of the control value. Release also fell below control by this time, but not as far. One week after denervation the release, 69 units per 3 hr, correspond to 3.3% of the reduced content of AChE activity in the muscle, indicating that denervation caused an increase in the proportion of AChE released. Sucrose density gradient ultracentrifugation showed that 10S AChE accounted for more than 80% of the released enzyme activity at all times. The results did not rule out the possibility, however, that the released enzyme originally stemmed from 4S or 16S AChE in the diaphragms.

Development of the multiple molecular forms of acetylcholinesterase in chick paravertebral sympathetic ganglia: an in vivo and in vitro study

The development of acetylcholinesterase (AChE) activity and the distribution of this enzyme among its multiple forms was studied in both tissue extracts and dissociated cell cultures of chick paravertebral sympathetic ganglia. In agreement with previous findings, total AChE (expressed either per ganglion or per microgram protein) increased in vivo between the time of formation of the paravertebral chain (embryonic day 7; E7) to hatching (E20-E21). After this time, enzyme activity changed much more slowly. Sucrose gradient sedimentation analysis of AChE in ganglia of post-hatching chicks revealed multiple forms of AChE with S values of approximately 6.5, 11 and 19.5. Developmental studies showed that 6.5 S and 11 S forms are present as early as day E7. Much of the pre-hatching increase in total AChE is due to increased levels of the 6.5 S form of the enzyme. By hatching, this form comprised approximately 85-90% of the total AChE activity. In contrast, during the first week after hatching, the activity of the 11 S form increased several-fold while that of the 6.5 S remained approximately unchanged. The 19.5 S form, which is thought to be associated with the synaptic membrane, was not detected prior to day E17 and reached adult levels (2-3% of total AChE activity) by the first week after hatching. Development of AChE was also studied in dissociated cell cultures of embryonic ganglia. Essentially all the AChE activity in such cultures was found to be associated with the neurons. Total AChE activity of cultured E11 ganglia increased in a pattern which was both qualitatively and quantitatively similar to that which occurred in vivol. Furthermore, it was found that development of both the 6.5 and 11 S forms of AChE took place in vitro. In cultures of E8, E11, E15 and E19 ganglia, the distribution of activity between the two forms after various times in vitro was similar to that which was found for in vivo ganglia at an equivalent embryonic stage. Such changes were not affected by the elimination of nonneuronal cells from the cultures. Two aspects of in vitro development, however, differed from that which occurred in vivo. First, an increase in 11 S AChE did not occur at ages equivalent to the first week post-hatching. Second, the 19.5 S form did not develop (even after several weeks) in cultures of E8, E11 and E15 ganglia, nor was this form (which was removed during dissociation of the ganglia) regenerated in cultures of E19 ganglia. Such findings suggest that the pattern of development of AChE and its multiple forms in chick sympathetic neurons is in part intrinsically programmed into these cells at an early stage of development as well as in part regulated by extrinsic signals that these cells receive from their chemical and cellular environment.