First Messengers

Abstract First messengers are broadly defined as any extracellular factor that elicits a response within a cell. As such, first messengers are incredibly diverse, ranging from environmental factors, such as light or heat, to small molecules and peptides, up through large multivalent proteins. Although there are thousands of first messengers, there are relatively few classes of receptors that can receive these signals and elicit a response within the cell. These receptor classes are ion channels, intracellular receptors, G-protein coupled receptors and single-pass transmembrane receptors. Although some individual first messengers are well characterised, this article attempts to create a more cumulative reference of the first messengers most common to vertebrates. Key Concepts: All species use a form of cellular communication known as signal transduction to respond to first messengers in their external environment. The diversity of molecules and stimuli that act as first messengers is vast. The variety of receptors classes that detect these molecules is surprisingly limited considering the wide variety of ligands utilised. Organisms use first messengers to receive information from the outside world as well as conduits for communication between cells.