Question

What would happen if you treated a long distance runner with a drug that prevented phosphate (Pi) from entering the sarcoplasmic reticulum of skeletal muscle? True or False ?

i. Maximum force would increase

ii. Sarcoplasmic reticulum Ca2+ release would be unaffected
iii. Fatigue would slow
iv. The drug will have little effect because the runner is an endurance athlete

v. The drug would be much more effective if it also prevented lactic acid production

Answer 1

The maximum force would increase - true

Explanation - During strenuous muscle activity, there is an increase in the phosphate. This enters in the sarcoplasmic reticulum and binds to the calcium. As a result, insoluble Calcium phosphate. This has the following effects:

1. Reduces calcium release in the sarcoplasmic reticulum
2. Reduces cross-bridge forces
3. Reduced calcium sensitivity of myofibrils

Sarcoplasmic reticulum Ca2+ release would be unaffected - false

explanation: Phosphate reduces calcium release into the sarcoplasmic reticulum.

Fatigue would slow - true

Explanation - if drug reduces the levels of phosphate in the sarcoplasmic reticulum, it will prevent

1. Reduction calcium release in the sarcoplasmic reticulum
2. Reduction cross-bridge forces
3. Reduction in calcium sensitivity of myofibrils

The drug will have little effect because the runner is an endurance athlete - False

Slow-twitch fibers also undergo fatigue but slow.

The drug would be much more effective if it also prevented lactic acid production - true

lactic acid is produced during glycolysis. Lactic acid accumulation has the following effects

• Reduces the pH of the muscle
• Reduces phosphocreatinine
• Phosphofructokinase is inhibited

The overall effect is reduced ADP re-phosphorylation. This also reduces the activity of the Na+-K+ ATPase pump.