Which of the mechanisms listed below are possible ways that epinephrine could ha

Question

Which of the mechanisms listed below are possible ways that epinephrine could have different effects on cells in different types of organs or organ systems?

Mechanism 1: Different types of target cells express different subtypes of cell surface receptors. Each receptor subtype is coupled to a different 2nd messenger system. Thus, when epinephrine binds to different receptor subtypes in different target organs, it causes different cellular responses (e.g., vasoconstriction versus vasodilation of a smooth muscle cell).  

Mechanism 2: Different types of target cells express the same subtypes of cell surface receptors; however, the receptors activate different downstream signaling pathways (e.g., different 2nd messenger systems or different patterns of activation or inactivation of proteins). Thus, when epinephrine binds to the same receptor subtypes on different target cells, it causes different cellular responses (e.g., vasoconstriction versus vasodilation of a smooth muscle cell).  

Answer Choices

A) Mechanism 1 is the only possible mechanism.

B) Mechanism 2 is the only possible mechanism.

C) Mechanisms 1 and 2 are both possible mechanisms.

D) Neither 1 nor 2 are possible mechanisms.

Explanation / Answer

The correct answer is - A) Mechanism 1 is the only possible mechanism.

Additional Information :

There are two main types of epinephrine receptor : Alpha & Beta.  Alpha receptor can be divided into two types : Alpha1 (coupled to Gqprotein , which acts via DAG and Ip3 and increases intracellular calcium concentration and therefore initiate smooth muscle contraction ) & Alpha2 (Coupled to Gi protein, which acts via adenylate cyclase - cAMP second messenger system and intiate smooth muscle contraction, inhibit transmitter release ) . Alpha1 receptor divided into Alpha1A, Alpha1B , Alpha1D . Alpha2 divided into Alpha2A , Alpha2B , Alpha2C .

Beta receptor divided into Beta1, Beta2, Beta3(coupled to Gs protein, which acts via adenylate cyclase - cAmp second messenger system and initiate heart muscle contraction, smooth muscle relaxation etc. Beta2 & Beta3, receptor can also be coupled to GI protein).

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