Soluble cholinesterase of muscle from dystrophic and normal mice

Acetylcholinesterase molecular forms in C57BL/6J dystrophic mice

Acetylcholinesterase (AChE) was extracted from normal and dystrophic C57BL/6J mouse hindlimb muscles and its molecular forms fractionated by sucrose density gradient ultracentrifugation. In the soleus muscles from 6- to 7-week-old mice an increase in the 3 Svedberg unit (S) and a decrease in the 16S AChE molecular forms was observed in dystrophic animals compared to controls. At 12-13 weeks of age, no major significant differences in the relative proportions of AChE molecular forms were noted. In the extensor digitorum longus (EDL) muscles of 6- to 7-week-old dystrophic mice a significant decrease in the proportion of the 10S AChE molecular form and an increase in the 3S and 5S forms was observed. At 12-13 weeks, the dystrophic EDL muscles again displayed a decrease in the 10S form; however, the increase in the 3S and 5S AChE forms, while still apparent, was not significant. These results provide evidence for a biochemical abnormality in the distribution of specific AChE molecular forms, and a differential expression of this abnormality in the soleus and EDL muscles.

The acetylcholinesterase abnormality in dystrophic mice is a reflection of a maturational defect

Juvenile mice of the ReJ/129 strain exhibit a distribution of acetylcholinesterase molecular forms that is similar to the pattern previously observed in dystrophic mice. The change to an adult distribution of the enzyme occurs at about 3 weeks of age which is also when dystrophic signs first become evident. It is suggested that dystrophic mouse muscle fails to mature with respect to the molecular forms of acetylcholinesterase.

Asymmetric and globular forms of AChE in slow and fast muscles of 129/ReJ normal and dystrophic mice

Acetylcholinesterase activities and molecular forms were studied in normal and dystrophic 129/ReJ mice, focusing on four predominantly fast-twitch muscles and the slow-twitch soleus. The asymmetric and globular forms were analyzed separately so that the effect of dystrophy on each form could be determined. This comparative study showed the following. (1) In the normal condition, each muscle exhibited a distinct distribution of the molecular forms. (2) The diversity among the fast muscles resulted mainly from variations in the proportions of the three globular forms; in contrast, these muscles showed a constant and precise A12/A8/A4 ratio. (3) The slow-twitch soleus clearly differed from the other muscles in its low acetylcholinesterase activity and distinct distribution of the molecular forms, characterized by a low level of G4 and a peculiar ratio among its asymmetric forms, resulting from a relative increase of the A8 and A4 forms. (4) In dystrophic mice, the diversity of the acetylcholinesterase distribution was lost; all the fast muscles displayed profiles exhibiting the characteristics typical of the soleus. The fast-twitch extensor digitorum longus, sternomastoid, and plantaris converged towards an identical set of acetylcholinesterase molecules. (5) In contrast, the acetylcholinesterase activity and molecular forms of the soleus were only slightly affected by the disease. These results reveal that the dystrophy modifies both categories of molecular forms of acetylcholinesterase in a very precise manner. Such complex changes, which are highly reproducible in a variety of different muscles, are unlikely to result from nonspecific reactions secondary to the disease.

Changes in muscle esterases in genetically dystrophic and control littermate mice

The hypothesis that the existence of a family of isoenzymes is at the basis of the heterogeneity of esterase activity among skeletal muscles from dystrophic Re 129J and control littermate mice was tested using isoelectrofocusing (IEF) in polyacrylamide gel. All muscles considered showed not only quantitative heterogeneity, as previously observed in this laboratory, but also qualitative differences with regard to their esterase isoenzymes. Differences in the number and the relative amounts of isoenzymatic bands were found between different muscles from both control and dystrophic animals. In most dystrophic muscles a new isoenzymatic band appeared at pH 6.6. Another band, identified at pH 5.12, was more pronounced in dystrophic than in control muscles. The specificity of these observations is indirectly supported by the fact that other tissue, such as heart, liver, and kidney, did not show the quantitative or qualitative abnormality present in the dystrophic skeletal muscles.

Acetylcholinesterase and butyrylcholinesterase released from normal and dystrophic muscles by treatment with proteolytic enzymes

1. Skeletal muscle from C57BL dystrophic mice demonstrated decreased activities of acetylcholinesterase with increased activities of butyrylcholinesterase. These changes were less distinct when compared to those observed with 129 ReJ mice. 2. Collagenase or trypsin treatment solubilized less acetylcholinesterase activity but more butyrylcholinesterase activity from muscle of C57BL dystrophic mice than from muscle of control mice. 3. These treatments resulted in similar pattern of release of acetylcholinesterase activity from muscle of 129 ReJ mice, except that more acetylcholinesterase activity was released from dystrophic muscle (129 ReJ) than from control by pepsin treatment. 4. The acetylcholinesterase activities released by proteolytic enzymes were characterized by sucrose density gradient centrifugation.

The membrane morphology of the neuromuscular junction, sarcolemma, sarcoplasmic reticulum and transverse tubule system in murine muscular dystrophy studied by freeze-fracture electron microscopy

'Dystrophic' mice of the 129/ReJ-dy strain have a genetic defect in Schwann cell proliferation and neuromuscular junction formation. The presynaptic membrane specializations associated with vesicle fusion and acetylcholine release, as well as the postsynaptic membrane specializations associated with acetylcholine receptivity, appear normal in these animals when visualized with freeze-fracture techniques. However, there is a reduction in the infolding of the postsynaptic membrane, which forms the secondary synaptic cleft at the motor endplate and is the site of acetylcholinesterase activity. The orthogonal arrays of the non-junctional sarcolemma are found on dystrophic muscles, but at lower than normal densities. These observations are made on muscle fibers in which the membrane molecular organization of the sarcoplasmic reticulum and transverse tubule systems appear normal. Several possible linkages between the deficit in myelination and the altered synaptic morphology are discussed in the context of neuromuscular interaction.

Cholinesterase in muscle of dystrophic hamsters (Bio-40.54)

Isozyme patterns of cholinesterase (ChE) from heart, tongue, and skeletal muscle of normal and dystrophic hamsters are presented. Two principal bands, bands 1 and 2, were evaluated. Band 1 migrates faster towards the anode than does band 2. While bands 1 and 2 stain for AChE and were found in control muscles, only band 2 was stained by a pseudocholinesterase (BuChE) and was decreased in samples from dystrophic hamsters. The decrease in BuChE was most pronounced in dystrophic heart muscle. The low level of BuChE measured for dystrophic animal tissue was similar to isozyme patterns found in embryonic tissue and in denervated muscle. BuChE obtained by acrylamide gel electrophoresis along with 16S AchE appears to be a useful biochemical marker of nerve-muscle interactions.

Collagenase-releasable and -resistant cholinesterases in normal and dystrophic muscles

The release of acetylcholinesterase activity by collagenase from the particulate fraction of mouse muscle homogenate into the soluble fraction was dependent on the time of incubation of muscle homogenate with collagenase. The collagenase-stimulated release of acetylcholinesterase was inhibited by 1,10-phenanthroline, an inhibitor of collagenase. Differential effects of inhibitors of specific acetylcholinesterase and nonspecific cholinesterase were observed in both collagenase extract and collagenase-resistant fraction derived from homogenate of muscle of normal and dystrophic mice. The collagenase extract of dystrophic muscle contained distinctly lower activity of acetylcholinesterase than that of normal muscle, while both collagenase extract and collagenase-resistant fraction of dystrophic muscle showed much higher activity of butyrylcholinesterase activity than those from normal muscle.