Diagram showing general types of receptor-mediated signal transduction. Transmembrane receptors may be either ionotropic (linked to ion channels) or metabotropic (linked to biochemical processes). Ionotropic receptors are drug ligand-gated transmembrane ion channels. Metabotropic receptors include G-protein-coupled receptors (GPCR) and other protein kinases. Intracellular receptors include cytosolic and nuclear receptors.