Final answer:
Epinephrine regulates glycogen breakdown in muscle cells, while glucagon stimulates glycogenolysis in liver cells.
Step-by-step explanation:
In muscle cells, epinephrine regulates the breakdown of glycogen into glucose, providing a ready pool of glucose for energy. In liver cells, glucagon stimulates the breakdown of stored glycogen into glucose through a process called glycogenolysis. This helps maintain blood glucose levels when they start to fall.