Question

How does cAMP gating of HCN (Hyperpolarization-Activated Cyclic Nucleotide-Gated) channels change under parasympathetic stimulation?

a) cAMP increases, leading to enhanced HCN channel activity.

b) cAMP decreases, resulting in decreased HCN channel activity.

c) cAMP has no effect on HCN channels.

d) cAMP activates HCN channels, but its control by parasympathetic stimulation is negligible.

Answer 1

Under parasympathetic stimulation, cAMP gating of HCN channels decreases, resulting in decreased HCN channel activity.

Step-by-step explanation:

Under parasympathetic stimulation, cAMP gating of HCN channels decreases, resulting in decreased HCN channel activity. Parasympathetic stimulation releases acetylcholine (ACh) which slows heart rate by opening chemical-gated potassium ion channels. This slows the rate of spontaneous depolarization, decreases HCN channel activity, and reduces the strength of contraction of the heart.