MEDizzy - Dopamine, epinephrine (or norepinephrine), and histamine are

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General pharmacology

Dopamine, epinephrine (or norepinephrine), and histamine are important neurotransmitter agonists. When these ligands interact with their cellular receptors, how do they mainly elicit their responses?

ExplanationThe key concept is that these very important agonists, and many others, “transduce” their signals and eventually change a characteristic of cell function (cause a response) through G proteins—a family of guanine nucleotide-binding proteins. These ligands bind to the extracellular face of the transmembrane protein. The various G proteins (e.g., Gi, Gq, Gs) bind to intracellular portions of the receptor. They then couple the initial ligand interaction to the eventual response through a series of effector enzymes or enzyme systems that are G protein-regulated. For example, adenylyl cyclase can be activated, catalyzing the formation of cAMP that then activates one or several kinases that phosphorylate specific intracellular proteins. But the actual steps that occur after ligand binding depend on what the ligand is, what specific G protein is involved, and which kinases are activated and what proteins they phosphorylate. And what happens (i.e., what the response is) depends on all of the above and, of course, which cell type is being affected. Activation of adenylyl cyclase and increased cAMP levels may occur in one system, but the opposite may occur in another. Some signal transduction The key concept is that these very important agonists, and many others, “transduce” their signals and eventually change a characteristic of cell function (cause a response) through G proteins—a family of guanine nucleotide-binding proteins. These ligands bind to the extracellular face of the transmembrane protein. The various G proteins (e.g., Gi, Gq, Gs) bind to intracellular portions of the receptor. They then couple the initial ligand interaction to the eventual response through a series of effector enzymes or enzyme systems that are G protein-regulated. For example, adenylyl cyclase can be activated, catalyzing the formation of cAMP that then activates one or several kinases that phosphorylate specific intracellular proteins. But the actual steps that occur after ligand binding depend on what the ligand is, what specific G protein is involved, and which kinases are activated and what proteins they phosphorylate. And what happens (i.e., what the response is) depends on all of the above and, of course, which cell type is being affected. Activation of adenylyl cyclase and increased cAMP levels may occur in one system, but the opposite may occur in another. Some signal transduction