Question

How can acetylcholine induce hyperpolarization?

Answer 1

Three types of hyperpolarization in response to applied acetylcholine (ACh) were observed in 4 identified neurones (RP1, RP2, RP3 and RP4) in the right parietal ganglion.

Explanation:

The results suggest that two currents may be mediated by different ACh receptors.
Details here:
https://www.ncbi.nlm.nih.gov/pubmed/2424560

Characterization of Acetylcholine-Induced Membrane Hyperpolarization in Endothelial Cells
http://circres.ahajournals.org/content/circresaha/70/2/257.full.pdf