Pharmacology General 9ce65c4f All 5-HT receptors are heptahelical serpentine receptors EXCEPT: A 5-HT1 B 5-HT2 C 5-HT3 D 5-HT4 High-Yield Explanation All serotonin receptors are G-protein coupled receptors except 5-HT3 which is an inotropic receptor.