9.3. Biochemical changes in muscles within pathology

During muscle diseases:

• the content of myofibrillar proteins, ATP, creatine phosphate, carnosine and anserin is reduced, ATP activity of myosin is decreased;

• the concentration of proteins and sarcoplasmic proteins of the stroma is increases;

• metabolism of creatine is disturbed and creatinuria occurs;

• activity of sarcoplasme enzymes is decreased and the activity of lysosomal enzymes is increased.

The content of cAMP in muscle tissue is decreased; the activity of phosphodiesterase is increased and the ability of adenylyl cyclase to be activated by adrenaline is disturbed.

During diseases associated with the breakdown of muscle tissue (progressive muscular dystrophy) phospholipid composition of muscles is changed: phosphatidylcholine and phosphatidylethanolamine level is decreased and the concentration of sphingomyelin is increased.

Patients with myopathy have disturbed synthesis of creatine phosphate and little production of creatinine. Creatinine in urine is decreased, and creatine index (creatine / creatinine) of urine is increased.

Ischemic heart disease. In the myocardium anaerobic metabolism is enhanced. Intracellular concentration of catecholamines and cAMP is increased; phosphofructokinase is activated (enzyme of glycolysis). Glycogen stores are depleted; there is acidosis. Membrane permeability is disrupted; potassium ions and enzymes leave the cells. There is disturbed oxidative phosphorylation, which leads to lower concentrations of ATP and creatine phosphate. The cells gradually die. Simultaneously changes the protein composition occur; carbohydrate, proteins and lipids metabolism is disturbed. Fatty acids are not oxidized and transformed into triglycerides, because of this there is fatty infiltration of the heart muscle. There is an increased activity of creatine kinase, lactate dehydrogenase and aspartate aminotransferase (test for myocardial injury) in blood serum.

Early test of myocardial damage is determination of myocardial-specific proteins in blood serum: myoglobin, troponin T.

Test Questions

11. How can you classify muscle fibers? Give them a brief characteristic.

2. List non-protein nitrogen extractive substances contained in the muscle.

3. What is the role of calcium ions in the biochemistry of muscle contraction?

4. Describe the mechanism of muscle contraction.

5. What processes provide muscle energy during short-term and long-term work?

6. Why is the heart muscle very sensitive to oxygen deficiency?

7. What biochemical changes occur in the muscles in coronary heart disease, myocardial infarction, myopathies, muscular dystrophy?

10. Biochemistry of extracellular matrix

10.1. Structure of extracellular matrix

Extracellular matrix is a substance that fills the spaces between cells. There are two parts – basement membranes and interstitial (fibroreticular) connective tissue.

Extracellular matrix serves as a framework, on which tissue is formed. In the tissues it binds cells together, supports the shape of cells and organs, and gives the mechanical strength of tissues. There is also a regulatory function.

Connective tissue is 50% of body weight. All varieties of connective tissue are built on common principles:

a) The intercellular matrix takes up more space than the cellular elements;

b) There are fibrillar structures surrounded by an interstitial substance;

c) The interstitial substance of connective tissue has a very complex chemical composition.

Matrix is built mainly of compounds of four classes.