Question

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, as shown in Figure Q16-32. Which of the following would enhance this effect of the acetylcholine?

(a) addition of a high concentration of a nonhydrolyzable 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

Answer 1

The option that would enhance the slowing effect of acetylcholine on heart rate is the addition of a high concentration of a nonhydrolyzable analog of GTP, which prolongs the activation of the G protein and keeps the K+ channels open longer. option a is answer

Step-by-step explanation:

The question concerns the biological mechanism by which acetylcholine affects heart rate through its interaction with G protein-coupled receptors (GPCRs) and downstream signaling pathways, specifically involving a K+ channel. Among the options given, the one that would enhance the effect of acetylcholine in slowing down the heart rate is:

Addition of a high concentration of a nonhydrolyzable analog of GTP. This analog would prevent the inactivation of the G protein, thereby prolonging the signal and keeping the K+ channels open longer, which would enhance the effect of acetylcholine.

The other options would either inhibit the signaling pathway or have no effect on enhancing the action of acetylcholine:

Addition of a drug that prevents the α subunit from exchanging GDP for GTP would inhibit the G protein activation, thereby reducing the effect of acetylcholine.

Mutations that weaken the interaction between the acetylcholine receptor and acetylcholine would make it more difficult for acetylcholine to bind and activate the receptor, thus reducing its effect.

Mutations that weaken the interaction between the acetylcholine receptor and the G protein would impede the signal transduction process necessary to open the K+ channels, thus diminishing the effect of acetylcholine. option a is answer