Glycosylation of Acetylcholinesterase Forms in Microsomal Membranes from Normal and Dystrophic Lama2dy Mouse Muscle

Abstract: The distribution and glycosylation of acetylcholinesterase (AChE) forms in vesicles derived from sarcoplasmic reticulum of normal muscle (NMV) were investigated and compared with those from dystrophic muscle vesicles (DMV). AChE activity was similar in NMV and DMV. Most of the AChE in NMV and half in DMV were released with Triton X-100. Asymmetric (A₁₂) and globular hydrophilic and amphiphilic (G^H₄, G^A₄, G^A₂, and G^A₁) AChE species occurred in NMV and DMV, the lighter forms being predominant. The percentage of G^H₄ and G^A₄ decreased in DMV. A fraction of the AChE that could not be extracted with detergent was detached with collagenase. Most of the detergent-released A₁₂ AChE from NMV and nearly half in DMV failed to bind to Ricinus communis agglutinin (RCA-I). Conversely, the collagenase-detached isoforms bound to RCA, revealing that asymmetric AChE associated with internal membranes or basal lamina differed in glycosylation. Moreover, nearly half of G^A₄ AChE in DMV and a few in NMV bound to RCA. Most of the RCA-unreactive G^A₄ forms in NMV come from sarcolemma. The results indicate that dystrophy induces minor changes in the distribution and glycosylation of AChE forms in internal membranes of muscle.     

Interaction of force transmission and sarcomere assembly at the muscle-tendon junctions of carp (Cyprinus carpio): ultrastructure and distribution of titin (connectin) and α-actinin

At muscle-tendon junctions of red and of white axial muscle fibres of carp, new sarcomeres are found adjacent to existing sarcomeres along the bundles of actin filaments that connect the myofibrils with the junctional sarcolemma. As the filament bundles that transmit force to the junction originate proximal to new sarcomeres, they probably relieve these new sarcomeres from premature loading. In red fibres, these filament bundles are long (up to 20 m) and dense, permitting light-microscopical immunohistochemistry (double reactions: anti-titin or anti--actinin and phalloidin). New sarcomeres have clear I bands; their A band lengths are similar to those of older sarcomeres and the thick filaments lie in register. T tubules are found at the distal side of new sarcomeres but terminal Z lines are absent. The late addition of -actinin suggests that -actinin mainly has a stabilizing role in sarcomere formation. The presence of titin in the terminal fibre protrusions is in agreement with its supposed role in sarcomere formation, viz. the integration of thin and thick filaments. The absence of a terminal Z line from sarcomeres with well-registered A bands suggests that this structure is not essential for the anchorage of connective (titin) filaments.     

Influence of central command and ergoreceptors on the splanchnic circulation during isometric exercise

The splanchnic circulation can make a major contribution to blood flow changes. However, the role of the splanchnic circulation in the reflex adjustments to the blood pressure increase during isometric exercise is not well documented. The central command and the muscle chemoreflex are the two major mechanisms involved in the blood pressure response to isometric exercise. This study aimed to examine the behaviour of the superior mesenteric artery during isometric handgrip (IHG) at 30% maximal voluntary contraction (MVC). The pulsatility index (PI) of the blood velocity waveform of the superior mesenteric artery was taken as the study parameter. A total of ten healthy subjects [mean age, 21.1 (SEM 0.3) years] performed an IHG at 30% MVC for 90 s. At 5 s prior to the end of the exercise, muscle circulation was arrested for 90 s to study the effect of the muscle chemoreflex (post exercise arterial occlusion, PEAO). The IHG at 30% MVC caused a decrease in superior mesenteric artery PI, from 4.84 (SEM 1.57) at control level to 3.90 (SEM 1.07) (P = 0.015). The PI further decreased to 3.17 (SEM 0.70) (P = 0.01) during PEAO. Our results indicated that ergoreceptors may be involved in the superior mesenteric artery vasodilatation during isometric exercise.     

The larval development of lateral musculature in gilthead sea bream Sparus aurata and sea bass Dicentrarchus labrax

Fibre-type differentiation of the lateral musculature has been studied in Sparus aurata (L.) and Dicentrarchus labrax (L.) during larval development. Histochemical and ultrastructural techniques show two presumptive muscle layers and two germinative zones of presumptive myoblasts. At hatching, myotomal muscle consists of a monolayer of thin undifferentiated cells near the skin (first germinative zone) overlying another mono-layer of small diameter fibres extending hypaxially and epaxially away from the transverse septum. Below this, there is a much thicker, deep layer of fibres, generally large in diameter and polygonal in shape. The presumptive myoblasts are located between these two layers of fibres in the second germinative zone. Initially, the superficial and deep muscle fibres show high and low myosin ATPase activity, respectively. Both layers grow by generating new fibres from the two mentioned germinative zones. At the end of larval life, the superficial layer changes its histochemical profile from high to low myosin ATPase activity and, at the same time, intermediate or pink muscle fibres can be observed by oxidative activity (the NADH-TR reaction). Morphometric analysis shows a significant increase in mean fibre diameter during successive ages, as shown by the Student's t-test (hypertrophic growth). Skewness and kurtosis values of fibre diameters point to the generation of a new fibre population from the germinative zones (hyperplastic growth).     

Schistosoma mansoni: differences in acetylcholine, dopamine, and serotonin control of circular and longitudinal parasite muscles

The physiological and pharmacological properties of circular and longitudinal somatic musculature in adult male Schistosoma mansoni were compared using cut muscle sections. Carbachol reduced tone in both circular and longitudinal muscle, but was without effect on circular muscle bathed in high Mg2+, indicating that cholinergic receptors were not associated with circular muscle membrane. 5-Hydroxytryptamine (5-HT) induced rhythmic contractile activity in both sets of muscle. It decreased muscle tone in circular muscle but increased the tone of longitudinal muscle. Metergoline blocked 5-HT effects on both sets of muscle. 5-HT continued to be effective on both sets of muscle bathed in high-Mg2+ medium, indicating that serotonergic receptors were present on both circular and longitudinal muscle membranes. Dopamine decreased both circular and longitudinal muscle tone. Its effects on circular muscle were still present after exposure to high Mg2+, but its effects on the longitudinal muscle were significantly reduced, leading to the conclusion that dopaminergic sites were probably associated with circular muscle membrane but not that of longitudinal muscle. Also, spiroperidol blocked stimulus responsiveness of the circular muscle but not that of the longitudinal muscle. From these studies it appears that there are significant physiological and pharmacological differences between circular and longitudinal muscles in the adult male schistosome.     

The innervation of the trachea and extrapulmonary bronchi of the mouse

Summary In the mouse, nerves were located throughout the trachea and extrapulmonary bronchi in both the smooth muscle and the connective tissue. However, no nerves were found within the epithelium. In the smooth muscle there were large numbers of nonmyelinated nerves. These were usually en passant elements but varicosities containing small mitochondria and vesicles were also seen; these axons sometimes appeared to be efferent to the muscle.Unilateral cervical vagotomy reduced the numbers of nerves in the muscle of the trachea and ipsilateral primary bronchus, suggesting that they were afferent. The intramuscular nerves were characterized in terms of their complement of cytoplasmic organelles; in particular nerves containing many mitochondria disappeared following vagotomy.Pretreatment of mice with 5-hydroxydopamine to accentuate the electron-opacity of catecholamine-containing granules resulted in 3.5% of the nerves within tracheal muscle showing such granules.The afferent nerves of the smooth muscle may be complex branching structures with many varicosities. The absence of epithelial nerves may be related to the absence of the cough reflex in the mouse.     

Ultrastructure of dynamic and static skeletofusimotor endings in a cat muscle spindle

Summary Endings of four skeletofusimotor axons in a spindle of the cat tenuissimus muscle were examined in semithin (1-m thick) and ultrathin transverse serial sections. Two (dynamic) axons terminated on the nuclear bag₁ intrafusal muscle fiber and on extrafusal fibers of the dark type. Two (static) axons terminated on the nuclear chain intrafusal fibers and extrafusal fibers of the intermediate type. The degree of indentation of axon terminals into the muscle surface, thickness of the sole plate and extent of folding of subjunctional membranes differed among intrafusal and extrafusal terminations of the same axon. Endings of axons on the bag₁ and chain fibers were also morphologically dissimilar. Motor axons may not determine ending morphology. Rather the form and structure of a bag₁ or chain ending may be determined by the type of intrafusal fiber on which the ending lies and the ending's distance from the primary sensory axon.     

Quantitative analyses of ultrastructure and vascularization of the slow muscle fibres of the anchovy

A quantitative study has been made of the ultrastructure and vascularization of slow fibres in the lateral muscles of the European anchovy (Engraulis encrasicolus). Mitochondria and myofibrils occupy 45.5 and 44.3% of total fibre volume respectively. More than 95% of all myofibrils are adjacent to mitchondria. A total of 51 % of the sarcolemma is in direct contact with capillaries with a mean of 12.9 capillaries per fibre. In transverse sections anchovy slow fibr es are considerably flattened (long to short axis 12:1) such that the surface to volume ratio is more than twice that of a cylindrical fibre of the same area (1115 μm²). The capillary surface required to supply l μm³ of mitochondria is 0.18 μm² and the maximum distance between any capillary and mitochondrion 8 μm. T-system and sarcoplasmic reticulum occupy 0.43 and 2.7% of fibre volume respectively. Adaptations for increasing the capacity of skeletal muscle for aerobic work are discussed.     

Fine structure and metabolism of multiply innervated fast muscle fibres in teleost fish

Summary Both the fast and slow muscle fibres of advanced teleost fish are multiply innervated. The fraction of slow-fibre volume occupied by mitochondria is 31.3%, 25.5% and 24.6%, respectively, for the myotomal muscles of brook trout (Salvelinus fontinalis), crucian carp (Carassius carassius), and plaice (Pleuronectes platessa), respectively. The corresponding figures for the fast muscles of these species are 9.3%, 4.6% and 2.0%, respectively. Cytochrome-oxidase and citrate-synthetase activities in the fast muscles of 9 species of teleost range from 0.20–0.93 moles substrate utilised, g wet weight muscle^-1 min^-1 (at 15° C) or around 4–17% of that of the corresponding slow fibres. Ultrastructural analyses reveal a marked heterogeneity within the fast-fibre population. For example, the fraction of fibres with <1% or >10% mitochondria is 0,4,42% and 36, 12 and 0%, respectively, for trout, carp and plaice. In general, small fibres (<500 m²) have the highest and large fibres (>1,500 m²) the lowest mitochondrial densities. The complexity of mitochondrial cristae is reduced in fast compared to slow fibres.Hexokinase activities range from 0.4–2.5 in slow and from 0.08–0.7 moles, g wet weight^-1 min^-1 in fast muscles, indicating a wide variation in their capacity for aerobic glucose utilisation. Phosphofructokinase activities are 1.2 to 3.6 times higher in fast than slow muscles indicating a greater glycolytic potential. Lactate dehydrogenase activities are not correlated with either the predicted anaerobic scopes for activity or the anoxic tolerances of the species studied. The results indicate a considerable variation in the aerobic capacities and principal fuels supporting activity among the fast muscles of different species. Brook trout and crucian carp are known to recruit fast fibres at low swimming speeds. For these species the aerobic potential of the fast muscle is probably sufficient to meet the energy requirements of slow swimming.