When epinephrine binds to cardiac (heart) muscle cells, it speeds their contraction. When it binds to muscle cells of the small intestine, it inhibits their contraction. Which of the following best accounts for the fact that the same hormone can have different effects on muscle cells?
Cardiac cells have more receptors for epinephrine than do intestinal cells
Epinephrine circulates to the heart first and thus is in higher concentration around cardiac cells
The two types of muscle cells have different signal transduction pathways for epinephrine and thus have different cellular responses
Cardiac muscle is stronger than intestinal muscle and thus has a stronger response to epinephrine