What happens to a muscle contraction if there is an excess amount of either Ca2 plus or ATP present during the contraction?

If there is an excess amount of either Ca2+ or ATP present during a muscle contraction, it can have different effects depending on the specific situation. Here's what happens in each case:

Excess Ca2+:

1. Prolonged Contraction: If there is an excess of Ca2+ ions available, the binding of Ca2+ to troponin will remain high even after the action potential has ended. This sustained binding prevents the detachment of myosin from actin, leading to a prolonged muscle contraction. This condition is known as "calcium overload" and can result in muscle stiffness and impaired relaxation.

2. Rigor Mortis: In extreme cases of calcium overload, the muscle may enter a state of permanent contraction known as rigor mortis. This occurs when the muscle cells are depleted of ATP and the myosin heads remain tightly bound to actin, preventing relaxation even after the nerve impulse has ceased. Rigor mortis typically sets in a few hours after death when cellular metabolism ceases and ATP production stops.

Excess ATP:

1. Faster Contraction and Relaxation: An excess amount of ATP can enhance the rate of muscle contraction and relaxation by facilitating the detachment of myosin heads from actin. ATP provides the energy required for myosin to release its grip on actin and reset for the next contraction cycle. With more ATP available, this process can occur more quickly, leading to faster muscle movements.

2. Increased Sustained Contractions: In some cases, an excess of ATP can also contribute to increased sustained contractions. When ATP is readily available, the muscle can maintain a high level of force production over a more extended period. This effect is often observed during intense exercise when muscles are working at high intensity and producing large amounts of ATP through anaerobic metabolism.

It's important to note that these effects are context-dependent and depend on the specific conditions within the muscle fiber. The optimal concentrations of Ca2+ and ATP for normal muscle function are tightly regulated by various cellular mechanisms to ensure proper muscle contraction and relaxation.