Developmental alterations in 5'-nucleotidase kinetics and lipid composition of rat heart sarcolemma

The objective of these studies was to examine the mechanism by which the specific activity of heart sarcolemma 5'-nucleotidase decreases as function of age. We examined the kinetic properties and the lipid composition of the sarcolemma from animals with different ages. The age groups used were 1 month, 6-8 months and 13-15 months. It was found that the Km of this enzyme increases as the animal develops from 1 month to 6-15 months. The opposite was true with 5'-nucleotidase Vmax. There was no significant difference between the middle age and the older age groups in those parameters. The results of these experiments suggest that the increase in Km in sarcolemma 5'-nucleotidase could be due to the reduction of the sarcolemmal polyunsaturated fatty acid concentration, the only lipid alteration observed.     

Muscle

Two important types of muscle are skeletal and smooth muscle. Their similarities and differences are described with regard to general morphology and ultrastructure (arrangement of filaments and T tubules), linking structure to physiological functions. The sliding-filament theory of muscle contraction is explained. Finally, the processes by which nerves excite muscle contraction (excitation–contraction coupling) are outlined, again relating variations in these processes in the two types of muscle to differences between them in their role in the body.     

Smooth muscle membrane organization in the normal and dysfunctional human urinary bladder: a structural analysis

PURPOSE: The decline in contractile properties is a characteristic feature of the dysfunctional bladder as a result of infravesical outlet obstruction. During clinical progression of the disease, smooth muscle cells undergo structural modifications. Since adaptations to constant changes in length require a high degree of structural organization within the sarcolemma, we have investigated the expression of several proteins, which are involved in smooth muscle membrane organization, in specimens derived from normal and dysfunctional organs. MATERIALS AND METHODS: Specimen from patients with urodynamically normal/equivocal (n = 4), obstructed (n = 2), and acontractile (n = 2) bladders were analyzed relative to their structural features and sarcolemmal protein profile. RESULTS: Smooth muscle cells within the normal urinary bladder display a distinct sarcolemmal domain structure, characterized by firm actin-attachment sites, alternating with flexible "hinge" regions. In obstructed bladders, foci of cells displaying degenerative sarcolemmal changes alternate with areas of hypertrophic cells in which the membrane appears unaffected. In acontractile organs, the overall membrane structure remains intact, however annexin 6, a protein belonging to a family of Ca2+-dependent, "membrane-organizers," is downregulated. CONCLUSION: Degenerative changes in smooth muscle cells, which are chronically working against high resistance, are preferentially located within the actin-attachment sites. In acontractile bladders, the downregulation of annexin 6 might have a bearing on the fine-tuning of the plasma membrane during contraction/relaxation cycles.     

Strength at the extracellular matrix-muscle interface

Mechanical force is generated within skeletal muscle cells by contraction of specialized myofibrillar proteins. This paper explores how the contractile force generated at the sarcomeres within an individual muscle fiber is transferred through the connective tissue to move the bones. The initial key point for transfer of the contractile force is the muscle cell membrane (sarcolemma) where force is transferred laterally to the basement membrane (specialized extracellular matrix rich in laminins) to be integrated within the connective tissue (rich in collagens) before transmission to the tendons. Connections between (1) key molecules outside the myofiber in the basement membrane to (2) molecules within the sarcolemma of the myofiber and (3) the internal cytoplasmic structures of the cytoskeleton and sarcomeres are evaluated. Disturbances to many components of this complex interactive system adversely affect skeletal muscle strength and integrity, and can result in severe muscle diseases. The mechanical aspects of these crucial linkages are discussed, with particular reference to defects in laminin-alpha2 and integrin-alpha7. Novel interventions to potentially increase muscle strength and reduce myofiber damage are mentioned, and these are also highly relevant to muscle diseases and aging muscle.     

利多卡因、异丙酚对缺血再灌注心肌细胞膜Na^＋—K^＋—ATP酶、肌浆网Ca^2＋—ATP酶活性的影响

目的观察利多卡因、异丙酚对缺血再灌注心肌细胞膜Na _K _ATP酶、肌浆网Ca2 _ATP酶活性的影响。方法SD大鼠48只 ,随机均分为6组。假手术组 ;生理盐水组 ;利多卡因5mg·kg-1 组 ;利多卡因10mg·kg-1 组 ;异丙酚300μg·kg-1·min-1 组 ;异丙酚1000μg·kg-1·min-1 组。于缺血前5min ,生理盐水及利多卡因经股静脉注射给药(30s内注射完) ;异丙酚持续输注至缺血开始时为止。结扎冠脉左前降支 ,造成左室前壁相应心肌组织缺血15min ,然后松开结扎线再灌注10min ,应用分光光度法测定心肌细胞膜Na _K _ATP酶、肌浆网Ca2 _ATP酶活性。结果利多卡因可明显地促进肌浆网Ca2 _ATP酶活性的恢复(P<0.05) ,大剂量时还促进心肌细胞膜Na _K _ATP酶活性的恢复(P<0.05)。异丙酚可显著地促进心肌细胞膜Na _K _ATP酶活性的恢复(P<0.05 ,P<0.001),大剂量时促进肌浆网Ca2 _ATP酶活性的恢复(P<0.05)。结论利多卡因、异丙酚可促进再灌注期间心肌细胞膜Na _K _ATP和肌浆网Ca2 _ATP酶活性的恢复 ,从而抑制钙超载而减轻心肌缺血再灌注损伤。     

牛磺酸对家兔心肌肌膜和磷脂脂质体脂质过氧化的影响

在家兔心肌肌膜和人工生物膜脂质体上,牛磺酸显著抑制氧自由基发生系统(FeCl_3和抗坏血酸)所引起的脂质过氧化物丙二醛的增加,其抑制作用呈剂量依赖和时间依赖关系。本结果证实牛磺酸具有抗氧化作用,在膜水平上直接起到自由基清除剂作用。     

Transport ATPases of Cardiac Sarcolemma in 20, 25-Diazacholesterol Induced Myopathy

Abstract. 20, 25-Diazacholesterol, known to induce myotonia in skeletal muscle, also affects cardiac muscle as can be concluded from the development of cardiomegaly. At the same time (Na⁺, K⁺) ATPase of cardiac sarcolemmal membranes of the 20, 25-diazacholesterol treated rats showed an increased activity as compared with control animals (91 % and 46 % stimulation respectively). The Ca⁺⁺ stimulated ATPase showed the same tendency (96 % and 64 % stimulation).
In the plasma of the treated rats creatine phosphokinase activity was found to be elevated whereas the amount of protein-bound iodine was decreased, a finding that is common in myotonic dystrophy.     

Correlation of dystrophin–glycoprotein complex and focal adhesion complex with myosin heavy chain isoforms in rat skeletal muscle

Aim: The dystrophin–glycoprotein complex (DGC) and focal adhesion complex (FAC) are transmembrane structures in muscle fibres that link the intracellular cytoskeleton to the extracellular matrix. DGC and FAC proteins are abundant in slow‐type muscles, indicating the structural reinforcement which play a pivotal role in continuous force output to maintain posture for long periods. The aim of the present study was to examine the expression of these structures across fast‐type muscles containing different myosin heavy chain (MHC) isoform patterns which reflect the fatigue‐resistant characteristics of skeletal muscle. Methods: We measured the expression of dystrophin and β1 integrin (representative proteins of DGC and FAC respectively) in plantaris, extensor digitorum longus, tibialis anterior, red and white portions of gastrocnemius, superficial portion of vastus lateralis and diaphragm, in comparison with soleus (SOL) and cardiac muscle from rats. Results: The expression of dystrophin and β1 integrin correlated positively with the percentage of type I, IIa and IIx MHC isoforms and negatively with that of type IIb MHC isoform in fast‐type skeletal muscles, and their expression was abundant in SOL and cardiac muscle. Conclusion: Our results support the idea that DGC and FAC are among the factors that explain the fatigue‐resistant property not only of slow‐type but also of fast‐type skeletal muscles.     

Disodium cromoglycate protects dystrophin-deficient muscle fibers from leakiness

In dystrophin-deficient fibers of mdx mice and in Duchenne dystrophy, the lack of dystrophin leads to sarcolemma breakdown and muscle degeneration. We verified that cromolyn, a mast-cell stabilizer agent, stabilized dystrophic muscle fibers using Evans blue dye as a marker of sarcolemma leakiness. Mdx mice (n=8; 14 days of age) received daily intraperitoneal injections of cromolyn (50 mg/kg body weight) for 15 days. Untreated mdx mice (n=8) were injected with saline. Cryostat cross-sections of the sternomastoid, tibialis anterior, and diaphragm muscles were stained with hematoxylin and eosin. Cromolyn dramatically reduced Evans blue dye-positive fibers in all muscles (P<0.05; Student's t-test) and led to a significant increase in the percentage of fibers with peripheral nuclei. This study supports the protective effects of cromolyn in dystrophic muscles and further indicates its action against muscle fiber leakiness in muscles that are differently affected by the lack of dystrophin.