When an ionotropic receptor is activated, it opens a channel that allows ions such as Na+, K+, or Cl− to flow.
In contrast, when a metabotropic receptor is activated, a series of intracellular events are triggered that can also result in ion channels opening or other intracellular events, but involve a range of second messenger chemicals.
[2] Chemical messengers bind to metabotropic receptors to initiate a diversity of effects caused by biochemical signaling cascades.
[5] Metabotropic receptors have a diversity of ligands, including but not limited to: small molecule transmitters, monoamines, peptides, hormones, and even gases.
Most of them are monomeric proteins, although GABAB receptors require heterodimerization to function properly.