Cells of the gastrointestinal (GI) tract and cells of the heart respond differently to epinephrine because __________.

• A. the GI tract does not have receptor tyrosine kinases
• B. in cells of the GI tract epinephrine operates via a cytosolic receptor, whereas in cells of the heart epinephrine acts via a plasma membrane receptor
• C. the concentration of Ca²⁺ is lower in the cytosol of GI-tract cells than in the cytosol of heart cells
• D. cells of the GI tract lack ATP
• E. there are differences in the proteins found in the two types of cells

Answer: (E)

Verified step by step guidance

1. Understand that epinephrine is a hormone that can have different effects on different types of cells due to the presence of different receptors or signaling pathways.
2. Recognize that the key to the problem is identifying why cells in the gastrointestinal (GI) tract and heart respond differently to the same hormone, epinephrine.
3. Consider the role of receptors: Epinephrine binds to specific receptors on the cell surface, and these receptors can vary between different cell types, leading to different cellular responses.
4. Acknowledge that the presence of different proteins, such as receptors or signaling molecules, in the cells of the GI tract and heart is a primary reason for the varied responses to epinephrine.
5. Conclude that the correct explanation is that there are differences in the proteins found in the two types of cells, which include receptors and other signaling proteins, leading to different responses to epinephrine.