K + channels in the heart do not have binding sites for ACh, yet parasympathetic release of ACh causes outward flux of K + from heart cells. How does this occur?
ACh triggers release of epinephrine from the adrenal glands, which in turn causes K+ flux out of heart cells.
ACh binds to a G-protein coupled receptor on heart cells, and the G protein alpha subunit binds to a separate K + channel and causes it to open.
Parasympathetic neurons activate sympathetic neurons, which directly cause K + flux from heart cells.
ACh binds and activates a K + pump on heart cells.