VPB 121: Veterinary Physiology - II (2+1)

METABOLISM OF GLUCOSE IN MUSCLE

• ATP formed during metabolism used for phosphorylating creatine, so creatine PO₄ formed. This creatine PO₄ used during contraction for phosphoylating ADP to form ATP and later ATP is hydrolyzed.
• ATP is also produced from FFA. Eg Palmitic acid generates 140 ATP
• FFA -----------> CO₂ + H2O + ATP
• Hence creatine kinase is used for restoring creatine PO₄ as well as to restore ATP. Approximately 0.3 μmol ATP is hydrolysed per gram of muscle during single twitch. Liver and skeletal muscle store glycogen of the animal body in equal proportion (9 to 16g of glycogen from 1 kg of skeletal muscle).
• FG muscles rely mostly on anaerobic glycolysis as the product of ATP is rapid and happens with out O₂. SOG and FOG cells relay on anaerobic metabolism for their energy production.
• Longer time required to obtain ATP through aerobic metabolism of glucose. Such muscle can sustain activity for longer periods of time (heart: only brief rest periods).
• During initial stages of contraction pH of sarcoplasm increases due to libration of creatine from creatine PO₄. But later pH decreases due to accumulation of lactic acid especially in anaerobic conditions.
• In anaerobic breakdown of glucose, lactic acid production is more which can alter the pH by altering the buffering capacity. So this type of metabolism is self limiting one. Lactic acid brings about fatigue.
• Liver can prepare glycogen from lactic acid more quickly than it is done by the muscles. Muscle can form glycogen more readily from glucose that it is done by the liver. Pyruvic acid partly converted to lactic acid in anaerobic condition.