Q. Acetylcholine acts at the G-protein-linked receptor on heart muscle to make the heart beat more slowly by the effect of the G protein on a K+ channel. Which one or more of next would enhance this effect of acetylcholine? Explain your reasoning to all answers.

(a) A high concentration of a non-hydrolyzable analog of GTP.

(b) Modification of acetylcholine-receptor-linked G protein α subunit by cholera toxin.

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

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

(e) Mutations in the G protein β subunit that weaken the interaction between βγ and K+ channel.