A unique acid phosphatase location: the transverse tubule of avian fast muscle

An ultrastructural study of the segmental uptake of horseradish peroxidase in the endplate region of denervated skeletal muscle fibres

The segmental uptake of horseradish peroxidase (HRP) in the endplate region of denervated skeletal muscle fibres has been studied ultrastructurally using a method for selecting single muscle fibres with high segmental peroxidase staining from denervated mouse tibialis anterior muscle. Segments containing large peroxidase positive phagosomes could already be seen 10-15 min after i.v. injection of HRP. Such segments were still present 24 h after HRP injection. The localization of phagosomes, deep in the fibres rather than immediately under the sarcolemma, suggests that the uptake occurs from t-tubuli. Vivid proliferation of t-tubuli, consisting of vesiculation, enlargement and encircling of cytoplasmic components, was also observed. The HRP accumulates in phagosomes of varying size and shape. Similar membrane-limited bodies without or with very weak peroxidase staining were also observed. The peroxidase-positive phagosomes participate in autophagic processes as suggested by their content of undegraded cellular material. Golgi profiles, which occurred deep in the muscle fibres, and enlarged components of the sarcoplasmic reticulum were frequently encountered in the segments. Myofibrillar degeneration occurs in the segments and progresses with time after denervation. The described segments may be related to the increased membrane turnover in denervated muscle fibres and/or they may be related to processes aimed at establishing new synaptic contacts.

Acid phosphatase activity in soleus and plantaris muscle fibres of normal and dystrophic hamsters. A quantitative histochemical study

The activity of acid phosphatase in skeletal muscle fibres of the plantaris and soleus of normal and dystrophic male hamsters was quantified using a histochemical post-coupling semipermeable membrane technique. Although the absolute levels of activity were found to vary widely from one animal to another, the ratio of the mean activities in the two muscles in each animal was virtually constant. In normal muscles, the ratio was about 0.73 and in dystrophic muscles, about 0.77. The activity in plantaris muscle fibres was always significantly lower than that in the corresponding soleus fibres, and in normal fibres compared to dystrophic ones. Another difference was that in normal fibres the mean activity declined to a constant level in mature animals older than about 3 months. In contrast, the activity in dystrophic muscles appeared to fall exponentially throughout life. The functional significance of these findings is discussed.

Multiple acid phosphatases in avian pectoral muscle--the postmicrosomal supernatant acid phosphatase is elevated in avian dystrophic muscle

There are at least three forms of acid phosphatase in avian pectoralis muscle differing in molecular weight, subcellular location, and response to various substrates and inhibitors. These enzymes are separated by differential sedimentation into postmicrosomal supernatant, lysosomal, and microsomal activities with apparent molecular weights in Triton X-100 of 68,000, 198,000, and 365,000, respectively. All of the enzymes show acid pH optima (pH approximately 5), but the postmicrosomal supernatant form is distinctly different from the other two forms in its resistance to most common phosphatase inhibitors and in its reduced activity against several organic phosphates. Quantitation of these three forms of acid phosphatase in normal and dystrophic avian pectoralis muscle shows that the postmicrosomal supernatant form is significantly elevated in dystrophic muscle; at 33 days ex ovo, 84% of the increased acid phosphatase activity in dystrophic muscle can be attributed to the postmicrosomal supernatant form. The microsomal form is only slightly elevated; the level of the lysosomal form is not altered.

Skeletal muscle lysosomes: comparison of lysosomes from normal and dystrophic avian pectoralis muscle as a function of age

The properties of skeletal muscle lysosomes from normal and dystrophic chickens were studied to assess their involvement in the dystrophic process. A method is described for isolation of a three-to-sevenfold purified lysosome fraction with 29-33% yield. Lysosomal enzymes in crude homogenates and isolated lysosome-enriched fractions from dystrophic muscle exhibit decreased latency for N-acetyl beta-D-glucosaminidase, acid phosphatase, and cathepsin D. However, no differences in the fragility of lysosomes in isolated lysosome-enriched fractions from normal and dystrophic muscle were observed using shear, sonication and detergent stress. Lower percent recovery, enrichment factor and percent latency of acid phosphatase compared to N-acetyl-beta-D-glucosaminidase and cathepsin D were observed from both normal and dystrophic muscle. These results are consistent with the presence of a significant amount of nonlysosomal acid phosphatase activity in skeletal muscle.

Fiber splitting in tonic and phasic skeletal muscles following denervation, chloroquine and triton WR-1339 treatments

Fiber splitting was studied in the tonic, anterior (ALD) and phasic, posterior (PLD) latissimus dorsi muscles using three experimental models, denervation, chloroquine administration and Triton WR-1339 administration. Fiber splitting was observed in the PLD in all three models, but in the ALD only after chloroquine administration. A basement membrane was always present in the split fibers, and acid phosphatase was localized between the split fibers in the PLD. However, no evidence of lysosomal involvement in the fiber splitting process was observed.

Further studies on a unique T-tubular acid phosphatase in avian skeletal muscle

With the unique observation, using conventional cytochemistry, of acid phosphatase reaction production in the T-tubules of the posterior latissimus dorsi muscle of the chicken, the possibility of endocytosis of lysosomal enzymes by muscle cells came into question. After testing the substrate specificity of this T-tubular phosphatase, it was clear that the enzyme hydrolysed glucose 6-phosphate and beta-glycerophosphate at pH 5.0 but not cytidine-5'-monophosphate which was hydrolysed by dense bodies and autophagic vacuoles. The cytochemical evidence points to a unique phosphatase present on muscle cell membranes which apparently does not belong to the vacuolar apparatus of skeletal muscle and is not 5'-nucleotidase.

Isopycnic-zonal centrifugation of plasma membrane, sarcoplasmic reticular fragments, lysosomes, and cytoplasmic proteins from phasic skeletal muscle

Homogenates of the posterior latissimus dorsi muscle, a phasic muscle, were fractionated by a one-step zonal centrifugation technique into four major organelle populations and cytoplasmic constituents. These were: (1) Plasma membrane fragments with a modal equilibrium density of 1.10 and containing 5'-nucleotidase, alkaline phosphodiesterase, p-nitrophenylphosphatase and acid phosphatase (beta-glycerophosphate was used as the substrate). (2) Sarcoplasmic reticular fragments which could be further subdivided into calcium transport vesicles, with a model equilibrium density of 1.16, that exhibited calcium uptake; K+-ATPase; leucyl-bet-naphthylamidase; acid phosphodiesterase; acid phosphatase (using cytidine monophosphate as the substrate); and sarcoplasmic reticular lysosomes, with a model equilibrium density of 1.18, possessing dipeptidyl-aminopeptidase II, cathepsin D, alpha-glucosidase, N-acetyl-beta-glucosaminidase, and NADH oxidase activity. (3) Mitochondria with a modal equilibrium density of 1.21. (4) Catalase-containing vesicles with a modal equilibrium density of 1.22; and cytoplasmic constituents (modal density of 1.25) with phosphorylase, pyruvate kinase, myosin-ATPase, aldolase, and protein and RNA content. The purity of these organelles was equal to or better than previous efforts, with a 30-fold purification achieved for 5'-nucleotidase and alkaline phosphodiesterase. These results lend support to the hypothesis that the sarcoplasmic reticulum of phasic muscle, in addition to its specialized role in excitation-contraction coupling, represents a multifunctional membrane system, and that, similar to the smooth endoplasmic reticulum of other cells, it includes some membrane-bound lysosomal enzymes and NADH oxidase.

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, 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.