Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K channel in the plasma membrane. Which of the following would enhance this effect of the acetylcholine

(a) addition of a high concentration of a non-hydrolyzable analog of GTP

(b) addition of a drug that prevents the α subunit from exchanging GDP for GTP

(c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine

(d) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein

The correct answer is option (b) "addition of a drug that prevents the α subunit from exchanging GDP for GTP".

Explanation:

The G protein is a name given to a family of proteins that act as a switch in diverse cellular processes, transmitting signals from outside to inside of the cells. When a G protein receptor is activated by a neurotransmitter such as dopamine, the alpha subunit exchanges its GDP for a GTP and disassociates G-protein itself. An addition of a drug that prevents this action would prevent  G protein disassociation, which would enhance the effect of stimulating G protein that acetylcholine does.

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