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.     

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.     

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)     

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.     

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 Role for Acetylcholine-Nicotinic Receptor Interactions in the Selective Increase of Rat Skeletal Muscle G4 Acetylcholinesterase Following Short-Term Denervation

The present work addresses the effects of short-term denervation on acetylcholinesterase (AChE; EC 3.1.1.7) isoenzymes in anterior gracilis muscles from adult male Sprague-Dawley rats. It examines possible relationships between AChE isoform changes and other denervation phenomena, and evaluates the importance of acetylcholine (ACh)-nicotinic receptor interactions in selectively modulating the activity of G4 AChE. Results confirm that denervation causes a specific, transient increase in G4 AChE and show that: most of the increment can be explained by the hydrophobic species of this isoenzyme; changes in AChE isoforms markedly precede the onset of spontaneous electromechanical activity (fibrillation), as well as acetylcholine receptor (AChR) proliferation; and the G4 AChE response is eliminated when AChRs are blocked by alpha-bungarotoxin treatment performed before but not after (24 h) denervation. These data point to the absence of direct causal relationships between the G4 AChE increment and fibrillation, AChR proliferation, or changes in the release of this isoform from denervated muscle. In turn, they suggest the participation of AChR activation in triggering the G4 AChE response and emphasize the possible role of ACh-AChR interactions in modulating the production of this isoenzyme in not only denervated but also innervated fast-twitch muscles.     

Interactions between intrinsic regulation and neural modulation of acetylcholinesterase in fast and slow skeletal muscles

1. Initiation of subsynaptic sarcolemmal specialization and expression of different molecular forms of AChE were studied in fast extensor digitorum longus (EDL) and slow soleus (SOL) muscle of the rat under different experimental conditions in order to understand better the interplay of neural influences with intrinsic regulatory mechanisms of muscle cells. 2. Former junctional sarcolemma still accumulated AChE and continued to differentiate morphologically for at least 3 weeks after early postnatal denervation of EDL and SOL muscles. In noninnervated regenerating muscles, postsynaptic-like sarcolemmal specializations with AChE appeared (a) in the former junctional region, possibly induced by a substance in the former junctional basal lamina, and (b) in circumscribed areas along the whole length of myotubes. Therefore, the muscle cells seem to be able to produce a postsynaptic organization guiding substance, located in the basal lamina. The nerve may enhance the production or accumulation of this substance at the site of the future motor end plate. 3. Significant differences in the patterns of AChE molecular forms in EDL and SOL muscles arise between day 4 and day 10 after birth. The developmental process of downregulation of the asymmetric AChE forms, eliminating them extrajunctionally in the EDL, is less efficient in the SOL. The presence of these AChE forms in the extrajunctional regions of the SOL correlates with the ability to accumulate AChE in myotendinous junctions. The typical distribution of the asymmetric AChE forms in the EDL and SOL is maintained for at least 3 weeks after muscle denervation. 4. Different patterns of AChE molecular forms were observed in noninnervated EDL and SOL muscles regenerating in situ. In innervated regenerates, patterns of AChE molecular forms typical for mature muscles were instituted during the first week after reinnervation. 5. These results are consistent with the hypothesis that intrinsic differences between slow and fast muscle fibers, concerning the response of their AChE regulating mechanism to neural influences, may contribute to different AChE expression in fast and slow muscles, in addition to the influence of different stimulation patterns.     

Difference in the ability of neonatal and adult denervated muscle to accumulate acetylcholinesterase at the old sites of innervation

In adult rat sternocleidomastoid muscle, AChE is concentrated in the region rich in motor end-plates (MEP). All major AChE forms, "16 S," "10 S," and "4 S," are accumulated at high levels, and not only "16 S" AChE. After denervation, muscle AChE decreases; 2 weeks after denervation, low levels (20-40% of control) are reached for all forms. During the following weeks, a slow but steady increase in "10 S" and "16 S" AChE occurs in the denervated muscle. At this stage, all forms are again observed to be highly concentrated in the region containing the old sites of innervation. Thus, in adult rat muscle the structures able to accumulate "16 S," "10 S," and "4 S" AChE in the MEP-rich regions remain several months after denervation. In normal young rat sternocleidomastoid muscle at birth, all AChE forms are already accumulated in the MEP-rich region. After denervation at birth, the denervated muscle loses its ability to keep a high concentration of "4 S," "10 S," and "16 S" AChE in the old MEP-rich region. All AChE forms are still present 1 month after denervation, but they are decreased and diffusedly distributed over the whole length of the muscle. In particular, "16 S" AChE is detected in the same proportion (10-15%) all along the denervated muscle. Thus, the diffuse distribution of AChE, and especially "16 S" AChE, after neonatal denervation, contrasts with the maintained accumulation observed in adult denervated muscle. It seems that denervation of young muscle results in a specific loss of the muscle ability to concentrate high levels of all AChE forms at the old sites of innervation.     

Extrasynaptic accumulations of acetylcholinesterase in the rat sternocleidomastoid muscle after neonatal denervation. Light and electron microscopic localization and molecular forms

Denervated neonatal rat sternocleidomastoid muscle has decreased levels of total AChE when compared to control muscle. Denervated versus control values of total muscle AChE present a three-phase curve in function of time after denervation. There is a rapid initial fall 0-3 days after denervation, an increase during about 2 weeks, then again a decrease in total AChE. Thus, there is a transitory net accumulation of AChE after the initial fall of activity in denervated developing muscle. Extrasynaptic areas of high AChE activity develop between 1 and 2 weeks after denervation and remain visible up to 1 month after denervation before vanishing. An electron microscope study shows that these accumulations are internal to the muscle fiber, close to a limited number of muscle nuclei and associated to the sarcoplasmic reticulum and nuclear envelope, but not to the T-tubule system. As found in adult rat muscle, the initial fall in AChE affects first the 16 S AChE form, and soon after, the 4 S and 10 S AChE forms. A main difference with adult muscle is the sudden increase and predominance over other forms of 10 S AChE 2 weeks after denervation at birth. Later, the decrease in AChE affects 16 S and 4 S AChE before 10 S AChE. The regions rich in extrasynaptic sites of AChE accumulation possess a very high proportion of 10 S AChE. Thus, the mechanisms of biosynthesis, intracellular transport and/or secretion of AChE may be very different in young, developing muscle compared to adult muscle.     

Acetylcholinesterase Molecular Forms in Chick Ciliary Ganglion: Pre- and Postsynaptic Distribution Derived from Denervation, Axotomy, and Double Section

Abstract: Four main molecular forms of acetylcholinesterase (AChE) characterized by their sedimentation coefficients (5S, 7.5S, 11.5S, and 20S), are found in chick ciliary ganglion. After transection of the preganglionic nerve (denervation), total AChE activity in the ganglion dropped by 35% in 2 days. By then, 11.5s and 20s forms had diminished by 60 and 75% respectively, where as 7.5s remained practically unchanged. Since presynaptic structures disappeared 2 days after denervation, we inferred that at most 35% of total ganglion AChE was presynaptic: 11.5s and 20s might be mainly presynaptic and 7.5S, postsynaptic. At later time intervals. total AChE continued to decline up to day 5, possibly as a result of orthograde transynaptic regulation of the enzyme activity. After transection of postganglionic nerves (axotomy), total ganglion activity showed little change; 11.5s and 20s decreased by 40 and 6076, respectively, in 5 days, but these drops were compensated for by an early increase in 7 5S, which started the day after axotomy. After simultaneous transection of both pre- and postganglionic nerves (double section), total ganglion AChE dropped rapidly by 35% in 1 day and remained at that level up to 21 days. The 11.5S diminished rapidly by 60% in 1 day. The early increase of the 7.5s form induced by axotomy alone did not occur. Since the effect resulting from double section was not the equivalent of the cumulative effects observed after denervation and axotomy, respectively, the level of AChE forms in the ganglion may be regulated by reciprocal interaction of pre- and postsynaptic elements. After denervation and double section but not after axotomy alone, the contralateral non-operated ganglion exhibited a fall in the 20s form. This suggests that a transynaptic effect is exerted on AChE by the contralateral preganglionic neuron. Taken together, these results indicate that the various AChE molecular forms in chick ciliary ganglion are preferentially but not exclusively distributed as follows: the pre- and postganglionic axons contain mainly the 11.5S form, whereas nerve endings and synaptic structures are enriched in 20S, and ganglion cell bodies, in 7.5s.     

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.     

DEVELOPMENT OF ACETYLCHOLINESTERASE MULTIPLE MOLECULAR FORMS IN CHICKEN MUSCLES

Abstract— AChE activity and protein content in chicken ALD and PLD muscles was studied during pre- and postnatal development. Protein content in both muscles increased whereas AChE activity increased in ALD and decreased in PLD during development. All studied values reached the steady-state 3 weeks after hatching.
Electrophoretic separation of the samples showed three molecular forms of AChE present in both adult ALD and PLD muscles. Two molecular forms in ALD muscle increased slowly, one form quickly. On the other hand, the activity of AChE forms in PLD muscle decreased with different rates. It appears from these results that the multiple molecular forms of AChE in muscles are not of the same physiological importance.     

Junctional form of acetylcholinesterase restored at nerve-free endplates.

Rat soleus muscles were ectopically innervated by implanting a foreign nerve in an endplate-free region of muscle and, 2–3 weeks later, cutting the original nerve. The junctional, 16 S form of acetylcholinesterase (AChE) and focal staining for AChE disappeared from the old endplate region within a few days after denervation. In muscles with an ectopic nerve, but not in paired control muscles, 16 S AChE and focal staining were restored in the old endplate region 1–2 weeks after denervation even though nerve fibers could not be detected in that region. These results suggest that the nerve exerts a local effect, specifying the site at which junctional AChE appears, and a nonlocal effect, perhaps mediated by muscle activity, regulating the amount of junctional AChE.     

ACETYLCHOLINESTERASE OF RAT SYMPATHETIC GANGLION: MOLECULAR FORMS, LOCALIZATION AND EFFECTS OF DENERVATION

Abstract— In sucrose gradient centrifugation, acetylcholinesterase (AChE, EC 3.1.1.7.) from the rat superior cervical ganglion (SCG) has been found to contain four molecular forms, characterized by their sedimentation coefficients (4 S, 6.5 S, 10 S and 16 S). Homogenization of the ganglia in various media showed that the 4 S enzyme was readily solubilized in water whereas solubilization of the 6.5 S and 10 S forms was quantitative only in media containing Triton X-100. In order to solubilize the 16 S form, high concentrations of salt (NaCl 1 M) and detergent had to be present. AChE analysed by non-denaturing polyacrylamide gel electrophoresis separated into five bands. Although both distribution patterns were stable, i.e. each form or band preserved its characteristic sedimentation or electrophoretic migration when reanalysed, there was no 1:1 correlation between the forms isolated by sedimentation and the bands obtained by electrophoresis: one band might contain more than one form of enzyme, and conversely one form gave rise to several bands. It was therefore impossible to derive molecular weights from electrophoretic migration in non-denaturing gels. However, it could be shown that the results obtained by both methods of analysis were consistent. Acetylcholinesterase from other nervous structures was analysed: in pre- and postganglionic nerves, the main forms were 10 S and 6.5 S, with a small proportion of 4 S; the 16 S form was not detected. In other sympathetic ganglia, the distribution of forms was identical to that of the superior cervical ganglion. In rachidian ganglia, no 16 S form could be found. Following the section of the preganglionic nerve, the acetylcholinesterase activity of the superior cervical ganglion decreased by 50% in 3 days, and then rose again to about 80% of its original value after 2 weeks. These effects mainly reflected variations in the major 4 S and 10 S forms. The 16 S form, in contrast to its disappearance from denervated muscles, increased transiently during the first 2 weeks after denervation, reaching about twice its original activity. A concomitant cytochemical study of normal and denervated ganglia showed that after preganglionic denervation, AChE localized in the sympathetic neurones decreased markedly and remained low even during the recovery phase. During this period a cholinesterasic activity appeared in the perineuronal glia. Controls established that the enzyme synthetized in the glia is AChE.     

Neurotrophic control of 16S acetylcholinesterase from mammalian skeletal muscle in organ culture

The effects of rat obturator nerve extracts on total and 16S acetylcholinesterase (AChE) activity were studied in endplate regions of denervated anterior gracilis muscles maintained in organ culture for 48 hr. The decrease of total AChE activity in cultured muscles was similar to that observed in denervated muscles in vivo. This decrease in activity was partly prevented by addition of either 100 or 200 μl nerve extract (2.7 mg/ml protein) to the nutrient medium. Nerve extract treatment also decreased the release of AChE activity from the muscle into the bathing medium. Conversely, rat serum (20 μl; 90 mg/ml protein) had no effect on total AChE activity in muscle endplates, nor on release of the enzyme by the muscle. The 16S form of AChE was confined to motor endplate muscle regions and its activity was drastically decreased by denervation in both organ culture and in vivo preparations in a comparable manner. Nerve-extract supplemented cultures contained a significantly (p ? 0.001) larger amount of endplate 16S AChE activity (140–145%) than the corresponding controls (100-). Our results suggest that some nerve soluble substance, other than serum contaminants or 16S AChE itself, affects the maintenance of 16S AChE at the neuromuscular junction.     

Modulation of the Acetylcholine System in the Superior Cervical Ganglion of Rat: Effects of GABA and Hypoglossal Nerve Implantation After In Vivo GABA Treatment

gamma-Aminobutyric acid (GABA) was applied to the superior cervical ganglion (SCG) of CFY rats in vitro and in vivo, with or without implantation of a hypoglossal nerve, to evaluate the effects of these experimental interventions on the acetylcholine (ACh) system, which mainly serves the synaptic transmission of the preganglionic input. Long-lasting GABA microinfusion into the SCG in vivo apparently resulted in a "functional denervation." This treatment reduced the acetylcholinesterase (AChE; EC 3.1.1.7) activity by 30% (p less than 0.01) and transiently increased the number of nicotinic acetylcholine receptors, but had no significant effect on the choline acetyltransferase (acetyl-coenzyme A:choline-O-acetyltransferase; EC 2.3.1.6) activity, the ACh level, or the number of muscarinic acetylcholine receptors. The relative amounts of the different molecular forms of AChE did not change under these conditions. In vivo GABA application to the SCG with a hypoglossal nerve implanted in the presence of intact preganglionic afferent synapses exerted a significant modulatory effect on the AChE activity and its molecular forms. The "hyperinnervation" of the ganglia led to increases in the AChE activity (to 142.5%, p less than 0.01) and the 16S molecular form (to 200%, p less than 0.01). It is concluded that in vivo GABA microinfusion and GABA treatment in the presence of additional cholinergic synapses has a modulatory effect on the elements of the ACh system in the SCG of CFY rats.     

THE MOTOR END-PLATE SPECIFIC FORM OF ACETYLCHOLINESTERASE: APPEARANCE DURING EMBRYOGENESIS AND RE-INNERVATION OF RAT MUSCLE

Abstract– We have solubilized three active molecular forms of AChE from rat muscle and have confirmed the presence of one of these forms (EP form, apparent sedimentation coefficient: 16 s) uniquely at the motor end-plate regions of several skeletal muscles. This form was never detected in smooth muscle extracts. In sternocleidomastoïdian muscle it disappeared after denervation and reappeared after re-innervation in the region where nerve and muscle had come in contact. During the embryonic development of hind leg muscles the EP form appeared on the 14th or 15th day of gestation.
The EP form of muscle AchE appears to be an excellent biochemical marker of the neuromuscular junction.     

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.