Muscle structure diseased

Multiminicore disease may also result from mutations in another protein found in the lumen of the ER/SR, selenoprotein N (Ferreiro 2002b). The function of selenoprotein N is currently unknown but may be to participate in regulation of redox homeostasis. An intriguing question is the relationship between RyRl and selenoprotein N such that mutations in either protein can produce similar changes in muscle structure and function. 

In a previous section we mentioned the significance of myosin filament structure. In nematodes two forms of myosin-II, myosin A and B, are required for proper filament stmcture (Epstein, 1988). The two forms of myosin are expressed at the proper time to allow for correct filament assembly. An accessory protein called paramyosin is also required for correct filament assembly. In vertebrate cardiac muscle, there are also two isoforms of myosin-II a-myosin and p-myosin. The proper ratio of these two proteins is of utmost importance for proper muscle activity. The incorrect synthesis of a- and P-myosins results in a severe cardiac disorder known as hypertrophic cardiomyopathy. Genetic transmission of the disease occurs in about 55% of families. The inherited condition is called familial hypertrophic cardiomyopathy (FHC), and this condition is a leading cause of sudden death in young athletes. 

Acquired disease of muscle is more common than is generally appreciated. It may result from the use of drugs—prescription or nonprescription—that have a recognized capacity to compromise the structure or function of skeletal muscle. Drugs particularly well recognized as myotoxic include clofibrate and its derivatives, anabolic steroids, penicillamine, and emetine. Many nonprescription drugs, including alcohol and laxatives, are directly or indirectly myotoxic. Other forms of acquired myopathies include the acute myopathic conditions caused by the bites of many snakes. 

In recent years free-radical species have been implicated in the pathogenesis of a wide variety of disorders (see Hal-liwell and Gutteridge, 1989), and attention has been drawn to the possibility that these agents might mediate some of the effects of excessive or unaccustomed exercise on muscle function and structure. In addition, free radicals may play a role in a number of muscle diseases. The aim of this short review is to examine these areas, drawing particular attention to those situations where the role of free radicals is controversial or where further studies are required. 

Squire,J. (1981). The Structural Basis of Muscle Contraction. Plenum Press, New York. Stefani, M., and Dobson, C. M. (2003). Protein aggregation and aggregate toxicity New insights into protein folding, misfolding diseases and biological evolution. J. Mol. Med. 81, 678-699. 

Cyclobenzaprine is structurally similar to tricyclic antidepressants. It acts at the brain stem level. It is used as an adjuvant agent for relieving muscle spasms associated with severe diseased conditions of the muscle. A synonym of this drug is flexeril. 

Pharmacology Cyclobenzaprine, structurally related to the tricyclic antidepressants (TCAs), relieves skeletal muscle spasm of local origin without interfering with muscle function. It is ineffective in muscle spasm caused by CNS disease. The net effect is a reduction of tonic somatic motor activity, influencing both gamma and alpha motor systems. 

Ox ocin is a nonapeptide which is structurally related to vasopressin. It stimulates rhythmic uterine contractions and is widely used by intravenous infusion of a diluted solution to induce labour and to treat postpartum bleeding. In large doses, it may cause relaxation of vascular smooth muscle causing hypotension in patients with cardiac disease or who are dehydrated. It has water-retaining properties and when given for prolonged periods to patients whose intake is electrolyte-free it causes overhydration and hyponatraemia. This may result in convulsions in the newborn with the risk of cerebral damage. 

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