USMLE Step 1 Question 314

Question:

A new drug is being developed to increase cardiac contractility in heart failure patients. Assuming the receptor of action of this drug also increases heart rate, which of the following is likely involved in the pathway of this drug’s signaling?

Correct Answer: D.  Protein kinase A

The drug in development is likely acting on the Beta-1 receptor in cardiac tissue, simultaneously increasing both contractility and heart rate. Beta-1, Beta-2, D1, H2, glucagon, and V2 receptors are Gs-protein-linked which act via adenylcyclase to create cAMP and eventually lead to increased protein kinase A as a second messenger. Alpha-1, M1, M3, H1 and V1 receptors are Gq-protein-linked, and act via phospholipase C to create either IP3 or DAG as second messengers. Zinc ion is a distractor in this question stem.