Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction?

Question

(a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero
(b) addition of a drug that blocks Ca2+ binding to troponin
(c) an increase in the amount of ATP in the cell
(d) a mutation in tropomyosin that decreases its affinity for the actin filament

Answer 1

(b) Ca2+ binding to troponin leads to a conformational change that causes a movement in tropomyosin so that myosin can bind to actin to initiate contraction. Thus, if troponin cannot bind Ca2+, the likelihood of contraction decreases. Partial depolarization of the T-tubule membrane will make it easier to depolarize the membrane, increasing the likelihood of muscle contraction [choice (a)]. ATP is required for myosin movement, so increasing the amount of ATP in the cell will not decrease contraction [choice (c)]. Tropomyosin normally binds to actin and blocks myosin binding, so a mutation in tropomyosin that decreases its affinity for actin should not decrease the likelihood of muscle contraction [choice (d)].