You Isolate Some Muscle Fibers to Examine What Regulates Muscle

Essay

You isolate some muscle fibers to examine what regulates muscle contraction.When you bathe the muscle fibers in a solution containing ATP and Ca²⁺, you see muscle contraction (experiment 3 in Table 17-22).Ca²⁺ is necessary, as solutions containing ATP alone or nothing do not stimulate contraction and thus the muscle remains in a relaxed state (experiments 1 and 2 in Table 17-22).From what you know about the mechanism of muscle contraction, fill in your predictions of whether the muscle will be contracted or relaxed for experiments 4, 5, and 6.Explain your answers. $\begin{array}{llcc} \text { Experiment } & \\ \text { number } & \text { added to muscle fibers}& \text {muscle state}\\\hline 1& \text { nothing } & \text {relaxed}\\\hline 2& \text { ATP } & \text {relaxed}\\\hline3& \text { ATP and \( \mathrm{Ca}^{2+} \) } & \text {contracted}\\ \hline4& \text { ATP, \( \mathrm{Ca}^{2+} \), and a drug that inhibits troponin from binding \( \mathrm{Ca}^{2+} \)} &\\\hline 5&\text { ATP and a drug that inhibits binding of tropomyosin to actin } &\\\hline 6&\text { a nonhydrolvzable analog of ATP } &\end{array}$

Table 17-22
Extra credit: In what state would the muscle be if you added Ca²⁺ but no ATP?