1. act directly on smooth m contractile machinery w/o APs: can cause contraction when m cell membrane contains excitatory receptors 2. can cause inhibition if membrane contains inhibitory receptors 3. contraction occurs by opening Na+/Ca2+ channels 4. inhibition= hormone closes Na/Ca2+ channels causing hyperpolarization of m (more - inside cell than normal) --ex. Ach, NE, E