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.     

Acetylcholinesterase in chick embryo latissimus dorsii muscles: effects of curarization and electrical stimulation

The accumulation of acetylcholinesterase (AChE), the changes in AChE-specific activity and in AChE molecular form distribution were studied in slow-tonic anterior latissimus dorsi (ALD) and in fast-twitch posterior latissimus dorsi (PLD) muscles of the chick embryo. From stage 36 (day 11) to stage 42 (day 17) of Hamburger and Hamilton, the AChE-specific activity decreased, while the relative proportion of asymmetric A 12 and A 8 forms increased. Repetitive injection of curare resulted at stage 42 (day 17) in a decrease in AChE-specific activity, in the accumulation of the synaptic AChE and in the expression of AChE asymmetric forms. Electrical stimulation at a relatively high frequency (40 Hz) of curarized ALD and PLD muscles resulted in a normal increase in AChE asymmetric forms, whereas a lower frequency (5 Hz) resulted in a dominance of globular forms. Both patterns of stimulation partly prevented the loss in synaptic AChE accumulations. These results suggest that in chick embryo muscles, muscle activity and its rhythms are involved in the normal evolution of AChE.     

Effects of Electrical Stimulation on Molecular Forms of Butyrylcholinesterase in Denervated Fast and Slow Latissimus Dorsi Muscles of Newly Hatched Chicken

The effects of denervation and direct electrical stimulation upon the activity and the molecular form distribution of butyrylcholinesterase (BuChE) were studied in fast-twitch posterior latissimus dorsi (PLD) and in slow-tonic anterior latissimus dorsi (ALD) muscles of newly hatched chicken. In PLD muscle, denervation performed at day 2 substantially reduced the rate of rapid decrease of BuChE specific activity which takes place during normal development, whereas in the case of ALD muscle little change was observed. Moreover, the asymmetric forms which were dramatically reduced in denervated PLD muscle were virtually absent in denervated ALD muscle at day 14. Denervated PLD and ALD muscles were stimulated from day 4 to day 14 of age. Two patterns of stimulation were applied, either 5-Hz frequency (slow rhythm) or 40-Hz frequency (fast rhythm). Both patterns of stimulation provided the same number of impulses per day (about 61,000). In PLD muscle, electrical stimulation almost totally prevented the postdenervation loss in asymmetric forms and led to a decrease in BuChE specific activity. In ALD muscle, electrical stimulation partially prevented the asymmetric form loss which occurs after denervation. This study emphasizes the role of evoked muscle activity in the regulation of BuChE asymmetric forms in the fast PLD muscle and the differential response of denervated slow and fast muscles to electrical stimulation.     

Differentiation of slow and fast muscles in chickens

1. The development of the characteristic histochemical appearance of the slow anterior latissimus dorsi (ALD) and fast posterior latissimus dorsi (PLD) was studied in chickens during embryonic development as well as during regeneration of minced muscle. 2. During embryonic development the activity of the oxidative enzyme succinic dehydrogenase (SDH) is higher in the slow ALD muscle already at 16 days of incubation. At this time the fast PLD has a higher activity of the glycolytic enzyme, phosphorylase. Although the histochemical appearance of the two types of muscle is already different at 16 days, their contractile speeds are still similar. No difference in myosin ATP-ase was found in the two muscles in young embryos but in 20-day old embryos the two muscles became distinctly different when stained for this enzyme. 3. When PLD muscles in hatched chickens redeveloped during regeneration in place of ALD the histochemical characteristics of the regenerated muscle resembled ALD, and when ALD regenerated in place of PLD it resembled PLD. 4. It is concluded that the histochemical characteristics of slow and fast muscles become determined during early development, even before any difference in contractile properties can be detected and that they are determined by the nerve.     

DEVELOPMENTAL CHANGES IN LEVELS AND FORMS OF CHOLINESTERASES IN MUSCLES OF NORMAL AND DYSTROPHIC CHICKENS

Abstract— Acetylcholinesterase (AChE) and pseudocholinesterase (°ChE) were studied in vivo and during the first several months of development of pectoral and posterior latissimi dorsi (PLD) muscles in normal and dystrophic chickens. Muscle extracts were prepared in a high ionic strength-nonionic detergent medium in the presence of protease inhibitors, in order to obtain complete solubilization and to prevent degradation of intrinsic molecular forms of both enzymes. In both normal and dystrophic pectoral muscles levels of AChE and °ChE increase rapidly in vivo, °ChE accounting for 5–10% of total cholinesterase activity. In the normal pectoral muscle the concentration of both enzymes drops rapidly after hatching with increasing muscle mass; total AChE per muscle remains relatively constant for 30 days post-hatch. In the dystrophic pectoral muscle both AChE and °ChE accumulate after hatching, resulting in greatly elevated levels (approx 10–25-fold) of both enzymes throughout the period studied. Multiple molecular forms of AChE and °ChE are observed in the pectoral muscle by sucrose gradient centrifugation. Four principal forms are distinguished: two light (L₁, L₂), one medium (M), and one heavy (H₂). The °ChE forms are 0.5–1.0 S units lighter than the corresponding AChE forms. L₂ is the predominant light form of AChE, whereas L₁ is the major light °ChE form detected. The lighter forms of AChE predominate in normal and dystrophic embryonic pectoral muscle at day 14, being replaced by the H₂ form by day 19. H₂ is the major °ChE form detected at day 19. After hatching, H₂ AChE is the predominant form found in both of the normal muscles studied. In the dystrophic pectoral muscle, progressive accumulation of the L₂ form of AChE is detected as early as day 4 post-hatch; this form eventually becomes predominant, although the heavier forms are also elevated. In PLD muscle the same phenomenon occurs, but with a slower time course. In dystrophic pectoral muscle a similar rise in the L₁ form of °ChE is first observed by day 4, with heavier forms also elevated in the mature muscle. Thus the alteration in the control of these two enzymes in dystrophic fast-twitch muscles results in an accumulation of the light forms of AChE and °ChE.     

Molecular forms of acetylcholinesterase in the slow muscle and the fast muscle of the chicken]

Five molecular forms of AChE are present in the slow (ALD) and twitch (PLD) muscles of the chick. These forms have 4 S, 7 S, 11 S, 15 S and 20 S sedimentation coefficient in sucrose gradient. The heaviest forms, the 20 S and 15 S of AChE are absent in uninnervated muscles and present in innervated muscles. In innervated muscles, the 20 S and 15 S AChE are present in both nerve-free segments and end-plates zones. The 20 S and 15 S which are not specifically associated with the end-plate zones in the chick could be considered as a biochemical "marker" of neuromuscular interactions.     

Neural influence on the expression of acetylcholinesterase molecular forms in fast and slow rabbit skeletal muscles

With the aim of investigating the roles of motor innervation and activity on muscle characteristics, we studied the molecular forms of acetylcholinesterase (AChE) in fast-twitch (semimembranosus accessorius; SMa) and slow-twitch (semimembranosus proprius; SMp) muscles of the rabbit. We have shown that SMa and SMp express different patterns and tissue distribution of AChE forms and that the effect of long denervation varies with age. Three principal findings concerning expression of AChE molecular forms emerge from these studies. (1) The activity of AChE and the pattern of its molecular forms are particularly altered in adult denervated SMa and SMp muscles. AChE activity increases by 10-fold in both muscles, but asymmetric forms disappear in SMa and increase by 20-fold in SMp muscles. A similar alteration of AChE is found after tenotomy of these muscles, showing that the effect of denervation may be partly due to suppression of muscle activity. (2) The different changes occurring in the composition of AChE molecular forms in adult denervated SMa and SMp muscles are consistent with fluorescent staining with anti-AChE monoclonal antibodies and with DBA or VVA lectins, which bind to AChE asymmetric, collagen-tailed forms. These lectins poorly stain denervated SMa muscle surfaces but intensely stain neuromuscular junctions and extrasynaptic areas in denervated SMp muscle. (3) In contrast with the adult, denervation of 1-day-old muscles does not markedly modify the total amount of AChE or the proportions of its molecular forms, despite dramatic effects on muscle structure. These results are supported by studies of labeling with fluorescent DBA: the lectin only slightly stains the muscle fiber surface of denervated 15-day-old SMp muscle. Taken together, these data show that denervated muscles escape physiological regulation, producing increased levels of AChE with highly variable cellular distribution and patterns of molecular forms, depending on the age of operation and on the type of muscle.     

Effects of electrical stimulation upon post-hatching development of fibre types in normally innervated fast and slow latissimus dorsii muscles of the chicken

In chicken, the main characteristic properties of muscle fibre types in slow anterior (ALD) and fast posterior (PLD) latissimus dorsii are acquired during post-hatching development. At day 4 it becomes possible to distinguish between alpha' and beta' fibre types in ALD muscle. At the same time, mATPase staining and NADH-TR activity permit recognition of alpha w and alpha R fibres within PLD muscle. During further development, muscle fibre typology progressively changes towards the adult slow and fast type. Chronic stimulation at a slow rhythm (5 Hz) of PLD prevents the change in relative proportions of alpha R and alpha W fibres within the muscle that occurs in normal post-hatching development and increases the number of beta R fibres. Moreover, oxidative activity is increased in all muscle fibre types following stimulation. In ALD muscle, chronic stimulation at a fast rhythm (40 Hz) results in a decrease in oxidative activity and inhibits the differentiation of alpha' and beta' muscle fibre types. This study demonstrates that in young chicken, the pattern of activity influences the differenciation of fibre types in slow and fast muscles.     

Comparison Between the Effects of Botulinum Toxin-Induced Paralysis and Denervation on Molecular Forms of Acetylcholinesterase in Muscles

Abstract: Velocity sedimentation analysis of acetylcholinesterase (AChE) molecular forms in the fast extensor digitorum longus muscle and in the slow soleus muscle of the rat was carried out on days 4, 8, and 14 after induction of muscle paralysis by botulinum toxin type A (BoTx). The results were compared with those observed after muscle denervation. In addition, the ability of BoTx-paralyzed muscles to resynthesize AChE was studied after irreversible inhibition of the preexistent enzyme by diisopropyl phosphorofluoridate. Major differences were observed between the effects of BoTx treatment and nerve section on AChE in the junctional region of the muscles. A precipitous drop in content of the asymmetric A12 AChE form was observed after denervation, whereas its decrease was much slower and less extensive in the BoTx-paralyzed muscles. Recovery of junctional AChE and of its A12 form after irreversible inhibition of the preexistent AChE in BoTx-paralyzed muscles was nevertheless very slow. It seems that a greater part of the junctional A12 AChE form pertains to a fraction with a very slow turnover that is rapidly degraded after denervation but not after BoTx-produced muscle paralysis. The postdenervation decrease in content of junctional A12 AChE is therefore not primarily due to muscle inactivity. The extrajunctional molecular forms of AChE seem to be regulated mostly by muscle activity because they undergo virtually identical changes both after denervation and BoTx paralysis. The differences observed in this respect between the fast and slow muscles after their inactivation must be intrinsic to muscles.     

Comparison of the Molecular Forms of the Cholinesterases in Tissues of Normal and Dystrophic Chickens

Abstract: The levels and molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and pseudocholinesterase (ΦChE, EC 3.1.1.8) were examined in various skeletal muscles, cardiac muscles, and neural tissues from normal and dystrophic chickens. The relative amount of the heavy (H_c) form of AChE in mixed-fibre-type twitch muscles varies in proportion to the percentage of glycolytic fast-twitch fibres. Conversely, muscles with higher levels of oxidative fibres (i.e., slow-tonic, oxidative-glycolytic fast-twitch, or oxidative slow-twitch) have higher proportions of the light (L) form of AChE. The effects of dystrophy on AChE and ΦChE are more severe in muscles richer in glycolytic fast-twitch fibres (e.g., pectoral or posterior latissimus dorsi, PLD); there is no alteration of AChE or ΦChE in a slow-tonic muscle. In the pectoral or PLD muscles from older dystrophic chickens, however, the AChE forms revert to a normal distribution while the ΦChE pattern remains abnormal. Muscle ΦChE is sensitive to collagenase in a similar way as is AChE, thus apparently having a similar tailed structure. Unlike skeletal muscle, cardiac muscle has very high levels of ΦChE, present mainly as the L form; AChE is present mainly as the medium (M) form, with smaller amounts of L and H_c. The latter pattern of AChE forms resembles that seen in several neural tissues examined. No alterations in AChE or ΦChE were found in cardiac or neural tissues from dystrophic chickens.     

Vinculin in subsarcolemmal densities in chicken skeletal muscle: localization and relationship to intracellular and extracellular structures

Using immunocytochemical methods we have studied the distribution of vinculin in the anterior and posterior latissimus dorsi skeletal (ALD and PLD, respectively) muscles of the adult chicken. The ALD muscle is made up of both tonic (85%) and twitch (15%) myofibers, and the PLD muscle is made up entirely of twitch myofibers. In indirect immunofluorescence, antivinculin antibodies stained specific regions adjacent to the sarcolemma of the ALD and PLD muscles. In the central and myotendinous regions of the ALD, staining of the tonic fibers was intense all around the fiber periphery. Staining of the twitch fibers of both ALD and PLD muscles was intense only at neuromuscular junctions and myotendinous regions. Electron microscopy revealed subsarcolemmal, electron-dense plaques associated with the membrane only in those regions where vinculin was localized by immunofluorescence. Using antivinculin antibody and protein A conjugated to colloidal gold, we found that the electron-dense subsarcolemmal densities in the tonic fibers of the ALD contain vinculin; no other structures were labeled. The basal lamina overlying the densities appeared to be connected to the sarcolemma by fine, filamentous structures, more enriched at these sites than elsewhere along the muscle fiber. Increased amounts of endomysial connective tissue were often found just outside the basal lamina near the densities. In tonic ALD muscle fibers, the subsarcolemmal densities were present preferentially over the I-bands. In partially contracted ALD muscle, subsarcolemmal densities adjacent to the Z-disk appeared to be connected to that structure by short filaments. We propose that in the ALD muscle, through their association with the extracellular matrix, the densities stabilize the muscle membrane and perhaps assist in force transmission.     

Functional transformation of fast posterior latissimus dorsi muscle by "slow" nerve implanted in newly hatched chickens.

1. Contraction properties and the activity of Ca2+ - ATPase were investigated 2 and 5 to 6 1/2 months after transposition of the fast posterior latissimus dorsi muscle (PLD) to the other side in newly hatched chickens. At the same time the muscle was cross-innervated by the nerve originally supplying the slow anterior latissimus dorsi muscle (ALD). 2. The mean isometric twitch contraction time of these transposed, cross-innervated PLD muscles in the 2-month-old and 5 to 6 1/2-month-old groups was 61.6 +/- 4.2 msec and 72.5 +/- 10.8 msec respectively. When compared with values obtained in control PLD and ALD muscles (21.9 +/- 0.6 msec and 107.7 +/- 5.6 msec), contraction time was significantly prolonged by this procedure. 3. Ca2+ - ATPase activity was also found to change towards the slow muscle (activity in control PLD was 0.600 micronmoles Pi/mg myosin/min, in the transposed, cross-innervated PLD 0.462 and in control ALD muscle 0.156 respectively). 4. Foreign innervation may thus induce changes in functional and biochemical properties even in muscles considerably different in structure and function, if transformation is allowed to take place at a sufficiently early stage of development. The muscle transposition itself, by introducing the element of muscle dedifferentiation and regeneration, probably assists the transformation process by making the muscle more plastic to the neural influences.     

Effect of spinal cord stimulation on the metabolism of developing latissimus dorsii muscles in chick embryo

Influence of chronic spinal cord stimulation upon some characteristic enzyme activities of energy metabolism was investigated in slow anterior (ALD) and fast posterior (PLD) latissimus dorsii muscles of the chick embryo. During embryonic life, oxidative metabolism (as evaluated by the activity of malate dehydrogenase (MDH] represents the main energetic pathway in both slow and fast muscles. At the end of embryonic life, an increase in anaerobic (as evaluated by the activity of lactate dehydrogenase (LDH] and creatine phosphokinase (CPK) activities occurs in PLD muscle. Chronic spinal cord stimulation at a low frequency was performed from the 10th day to the 16th day of embryonic development. In ALD, the enzyme activities were unaffected, while in PLD a concomitant decrease in LDH and CPK activities was observed.     

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.     

A freeze-fracture study of postembryonic differentiation of latissimus dorsi muscles of the chicken

The differentiation of fiber type characteristics in the anterior (ALD) and posterior (PLD) latissimus dorsi muscles is examined by the freeze-fracture technique in 1-, 7- and 30-day-old chicks. Several characteristics of plasma membrane (caveolae, rectilinear arrays, intramembranous particles) and sarcoplasmic reticulum which show fiber type differences in the adult ALD and PLD muscles are compared in the developmental stages. The caveolar density in the ALD fibers is about 20/microns2 at 1 day increasing to about 37/microns2 at 30 days, whereas in the PLD fibers it remains at about 20/microns2 during this period. The distribution of the caveolae in the two muscles is different from the beginning; in the ALD fibers the caveolae are distributed throughout the plasma membrane and in PLD fibers they are patterned into clusters overlying the I band regions. The density of intramembranous particles of 1-day ALD and PLD plasma membranes appears similar, but by 7 days the particle counts in the sarcolemma of the ALD muscle are about twice as numerous as those in the PLD muscle. The rectilinear arrays are virtually absent in the ALD muscle, whereas in the PLD muscle their density is about 10/microns2 at 1 day and about 20/microns2 at 7 days. Already at 1 day posthatching the SR in ALD and PLD fibers has the adult configuration, i.e., an open irregular network in ALD fibers and periodically arranged tubules with triadic expansions in the PLD fibers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased autophagy in chloroquine-treated tonic and phasic muscles: An alternative view

Ultrastructural and cytochemical techniques were used to investigate autophagy in the tonic anterior (ALD) and phasic posterior (PLD) latissimus dorsi muscles of the chicken following chloroquine administration. Autophagic vacuoles were seen in the ALD after 1 day of chloroquine administration while no change was seen in the PLD until 3 days. In both muscles, autophagic vacuoles and myeloid bodies were found at the level of the I band. Myeloid bodies usually were found in the longitudinal rows of mitochondria in the ALD muscle. Some, but not all, of the autophagic vacuoles and myeloid bodies were cytochemically acid phosphatase positive, while the portion of the sarcoplasmic reticulum of both muscles which is normally acid phosphatase positive was devoid of activity following chloroquine administration. These observations are discussed in regard to accepted mechanisms of autophagy and the possible inhibition of autophagy in skeletal muscle tissue by chloroquine.     

Skeletal muscle myopathy caused by Triton WR-1339

After administration (1 g/kg every other day for a total of five injections) of Triton WR-1339, the tonic, anterior (ALD) and phasic, posterior (PLD) latissimus dorsi muscles of the chicken underwent distinct pathological modifications. Some of the morphological alterations in the muscles paralleled those seen after administration of chloroquine, increased autophagic vacuole formation in the ALD muscle and swelling of the sarcoplasmic reticulum in the PLD muscle, but other changes were unique to Triton WR-1339. These included loss of myofilaments and whole myofibrils, indentation of the sarcolemma as well as increased numbers of ribosomes in the ALD muscle and swelling of the T-tubular system in the PLD muscle. These results are compared with other lysosome mediated pathologies, as well as with other myopathies.     

Immunochemical analysis of protein isoforms in thick myofilaments of regenerating skeletal muscle

The expression of myosin heavy chain (MHC) and C-protein isoforms has been examined immunocytochemically in regenerating skeletal muscles of adult chickens. Two, five, and eight days after focal freeze injury to the anterior latissimus dorsi (ALD) and posterior latissimus dorsi (PLD) muscles, cryostat sections of injured and control tissues were reacted with a series of monoclonal antibodies previously shown to specifically bind MHC or C-protein isoforms in adult or embryonic muscles. We observed that during the course of regeneration in each of these muscles there was a reproducible sequence of antigenic changes consistent with differential isoform expression for these two proteins. These isoform switches appear to be tissue specific; i.e., the isoforms of MHC and C-protein which are expressed during the regeneration of a "slow" muscle (ALD) differ from those which are synthesized in a regenerating "fast" muscle (PLD). Evidence has been obtained for the transient expression of a "fast-type" MHC and C-protein during ALD regeneration. Furthermore, during early stages of PLD regeneration this muscle contains MHCs which antigenically resemble those found in the pectoralis muscle at embryonic and early posthatch stages of development. Both regenerating muscles express an isoform of C-protein which appears immunochemically identical to that normally expressed in embryonic and adult cardiac muscle. These results support the concept that isoform transitions in regenerating skeletal muscles qualitatively resemble those found in developing muscles but differences may exist in temporal and tissue-specific patterns of gene expression.     

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)     

Decreased G4 (10S) Acetylcholinesterase Content in Motor Nerves to Fast Muscles of Dystrophic 129/ReJ Mice: Lack of a Specific Compartment of Nerve Acetylcholinesterase?

Acetylcholinesterase (AChE; EC 3.1.1.7) activity and the distribution of its molecular forms were studied in the nervous system of normal and dystrophic 129/ReJ mice, including the sciatic-tibial nerve trunk and motor nerves to slow- and fast-twitch muscles. In normal mice, motor nerves to the slow-twitch soleus exhibited a low AChE activity together with a low level of G4 (10S form) as compared with nerves of the predominantly fast-twitch plantaris and extensor digitorum longus. In contrast, in dystrophic mice, the AChE activity as well as the G4 content of nerves to the fast-twitch muscles were low, displaying an AChE content similar to that of the nerve of the soleus muscle. In the sciatic-tibial nerve trunk, the AChE activity decreased along the nerve in an exponential mode, at rates that were similar in both conditions. However, in dystrophic mice, the AChE activity was reduced throughout the nerve length by a constant value of approximately 180 nmol/h/mg protein. Further analyses indicated that AChE in this nerve trunk was distributed among two compartments, a decaying and a constant one. The decay involved exclusively the globular forms. The activity of A12 (16S form) remained constant along the nerve and was similar in both normal and dystrophic mice. In addition, according to the equation describing the decay of AChE, the reduction in enzymatic activity observed in the dystrophic mice affected mainly G4 in the constant compartment. Brain, spinal cord, sympathetic ganglia, and serum, which were also examined, showed no remarkable differences between the two conditions in their G4 content. The AChE abnormalities that we found in nervous tissues of 129/ReJ dystrophic mice were confined to the motor system.