The relation of energy-rich phosphate in muscle to myoglobin and to cytochrome-oxidase activity

Non-traumatic and non-drug-induced rhabdomyolysis

Rhabdomyolysis (RM), a fortunately rare disease of the striated muscle cells, is a complication of non-traumatic (congenital (glycogen storage disease, discrete mitochondrial myopathies and various muscular dystrophies) or acquired (alcoholic myopathy, systemic diseases, arterial occlusion, viral illness or bacterial sepsis)) and traumatic conditions. Additionally, RM can occur in some individuals under specific circumstances such as toxic substance use and illicit drug abuse. Lipid-lowering drugs in particular are capable of causing RM. This comprehensive review will focus on non-traumatic and non-drug-induced RM. Moreover, the pathology of RM, its clinical manifestation and biochemical effects, and finally its management will be discussed.

Thyrotoxicosis Presenting as Unilateral Drop Foot

Neuromuscular disorders associated with hyperthyroidism have several variations in their clinical phenotype, such as ophthalmopathy, periodic paralysis, and thyrotoxic myopathy. We herein report an unusual case of thyrotoxic myopathy presenting as unilateral drop foot. Histopathological examinations of the left tibialis anterior muscle showed marked variation in the fiber size, mild inflammatory cell infiltration, and necrotic and regenerated muscle fibers with predominantly type 1 fiber atrophy. Medical treatment with propylthiouracil resulted in complete improvement of the left drop foot. This case expands the phenotype of thyrotoxicosis and suggests that thyrotoxicosis be considered as a possible cause of unilateral drop foot.

Myoglobin and mitochondria: a relationship bound by oxygen and nitric oxide

Since their initial discovery over a century ago, our knowledge of the functions of myoglobin and the mitochondrion has gradually evolved. The mitochondrion, once thought to be solely responsible for energy production, is now known to be an integral redox and apoptotic signal transducer within the cell. Likewise, myoglobin, traditionally thought of only as an oxygen store, has emerged as a physiological catalyst that can modulate reactive oxygen species levels, facilitate oxygen diffusion and scavenge or generate nitric oxide (NO) depending on oxygen tensions within the cell. By virtue of its unique ability to regulate O(2) and NO levels within the cell, myoglobin can modulate mitochondrial function in energy-demanding tissues such as the beating heart and exercising muscle. In this review, we present the conventional functions of myoglobin and mitochondria, and describe how these roles have been reassessed and advanced, particularly in the context of NO and nitrite signaling. We present the mechanisms by which mitochondria and myoglobin regulate one another within the cell through their interactions with NO and oxygen and discuss the implications of these interactions in terms of health and disease.

Effect of exercise on the motor unit

The motoneuron part of this review deals with the changes in recruitment and firing rates of the motor unit types upon changes from a physically inactive life to endurance or strength training. The muscle fibers react to prolonged exercise by adaptation to a higher level of performance. A matter of discussion is the prerequisites for a transformation between the basic muscle fiber types, slow twitch and fast twitch, during voluntary (transsynaptic) activity, which is demonstrated after artificial nerve stimulation. The review includes current knowledge of muscle fiber transformation as an adaptive response to increased usage either by electrical stimulation or by transsynaptic neuronal activity. The metabolic adaptation related to increased endurance is reviewed with special reference to effects on muscle fibers. The increase in strength as a result of high resistance training is mainly the result of increased muscle cross-section. Whether this is solely the result of an increase in size of individual fibers or an increased fiber number is a controversial matter.

A morphometric analysis of human muscle fibers with relation to fiber types and adaptations to exercise

Muscle biopsies were obtained from the vastus lateralis of 14 male subjects: 3 long distance runners, 2 world class power lifters and 9 active, although not highly trained, individuals used as controls. The fibers were investigated by electron microscopy and the mitochondrial volume percent, lipid volume percent and Z-line width were analyzed morphometrically. With the combined data a direct correlation was found between mitochondrial volume percent and lipid volume percent, lipid volume percent and Z-line width and mitochondrial volume percent and Z-line width. The muscle fibers were classified as slow-twitch oxidative (SO), fast-twitch-oxidative-glycolytic (FOG) and fast-twitch-glycolytic (FG) based on relationships found in the data and well established properties of muscle fiber types. Although no distinct patterns emerged, a good approximation of fiber type characteristics was obtained, and values for volume percent of central mitochondria, volume percent lipid and Z-line width are reported. The fibers classified as SO were characterized by having wide Z-lines, a high mitochondrial volume percent and high lipid volume percent. The fast-twitch fibers (fibers with narrow Z-lines) were separated into 2 groups, those with high mitochondrial volume percent (FOG) and those with low mitochondrial volume percent (FG). No distinction could be made between the fast-twitch subgroups with regard to Z-line width. The fibers from distance runners differed from those from controls by exhibiting a greater capacity for aerobic activity as evidenced by the increased volume percent of mitochondria and lipid in both slow- and fast-twitch fibers. The high strength, anaerobic activity of the world class power lifters was reflected by the low mitochondrial volume percent of many fast-twitch fibers (FG) and the decreased lipid stores in all fibers.

The relationship of blood flow to myoglobin, capillary density, and twitch characteristics in red and white skeletal muscle in cat

1. The fractional distribution of blood flow was measured by the isotope dilution method and absolute blood flow estimated in twenty-four muscles of chronically prepared, unanaesthetized cats.2. In the quiet, alert cat the estimated mean muscle blood flow ranged from 5.9 to 39.3 ml./min 100 g muscle. Flow was three times greater in grouped red than white limb muscles.3. The myoglobin concentration ranged from 0.88 to 3.91 mg/g muscle. The myoglobin concentration of grouped red exceeded that of white muscle and varied in each muscle directly and linearly with blood flow with a high correlation (P < 0.001).4. Capillary density was estimated by determination of alkaline phosphatase activity. Alkaline phosphatase activity was significantly greater in red than white muscles and varied directly with fractional blood flow in these same muscles with a high correlation (P < 0.001).5. Contraction time was generally two to three times longer in red than white muscle. There was a direct and highly correlated relationship (P < 0.001) between blood flow and contraction time.6. The direct linear relationship between muscle blood flow and myoglobin concentration, capillary density, and contraction time characteristic of quiet wakefulness was lost during rapid eye movement sleep or excitement produced by electrical stimulation of the hypothalamus as a consequence of selective changes in flow in red and white skeletal muscle.7. The type of metabolism of any skeletal muscle is adapted to its activity during quiet, alert behaviour, rather than during sleep or excitement.