Which of the following describes a sequence which will ultimately activate glycogen breakdown in a muscle? A)epinephrine binds β receptors.$\to$cAMP $\to$ PKA $\to$phosphorylase kinase $\to$glycogen phosphorylase B)epinephrine bind α receptors $\to$ Ca²⁺ increase $\to$phosphorylase kinase $\to$ glycogen phosphorylase C)glucagon $\to$ glucagon receptors $\to$ cAMP $\to$ PKA $\to$ phosphorylase kinase $\to$ glycogen phosphorylase D)PP1 binding to unphosphorylated Gm $\to$ dephosphorylates glycogen phosphorylase and phosphorylase kinase E)All of these will activate glycogen breakdown in a muscle.

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Epinephrine binds to β receptors on muscle cells, leading to the activation of cAMP, which activates PKA. PKA then activates phosphorylase kinase, which in turn activates glycogen phosphorylase, ultimately leading to glycogen breakdown in the muscle. Choice B describes a pathway involving calcium signaling, which is not the primary mechanism for glycogen breakdown in muscle. Choice C describes the pathway for glycogen breakdown in liver, not muscle. Choice D describes the opposite process, where PP1 dephosphorylates glycogen phosphorylase and phosphorylase kinase, leading to their inactivation and inhibition of glycogen breakdown.

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