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. Would the following enhance or diminish the effect of Ach?
(a) addition of a high concentration of a non-hydrolyzable analog of GTP
(b) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein
(c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine
(d) addition of a drug that prevents the ? subunit from exchanging GDP for GTP