The beta-2 adrenergic receptor, also known as ADRB2, is a cell membrane-spanning beta-adrenergic receptor that binds epinephrine, a hormone and neurotransmitter whose signaling, via adenylate cyclase stimulation through trimeric Gs proteins, increased cAMP, and downstream L-type calcium channel interaction, mediates physiologic responses such as smooth muscle relaxation and bronchodilation. Wikipedia