Receptor, usually a protein that changes biological processes, they can be bound by drugs or poisons, which can activate, block (preventing other substances from activating said receptor) or inversely activate (basically activate a receptor in a way that causes the opposite effect to the endogenous ligand).
Autoreceptors vs. heteroreceptorsEdit
There are also autoreceptors which reduce the release of the neurotransmitter that they respond to, and heteroreceptors that reduce the release of a different neurotransmitter than the one that they respond to.
Inhibitory vs. excitatoryEdit
Agonist, a substance that activates a receptor. Antagonist, a substance that blocks a receptor, preventing agonists from binding to the receptor, in order to activate said receptor. Partial agonists, serve as agonists that produce a less complete activation of the receptor in question, when compared to full agonists. Full agonists produce an activation of the receptor, in question, that is equivalent to that produced by the endogenous ligand. Inverse agonists, elicit the reverse biologic response of agonists (hence why they are called “inverse” agonists).
Many drugs initially thought were antagonists were in fact inverse agonists like antihistamines, for example.
Receptor signalling mechanismsEdit
There are two major types of receptor: ionotropic (or ligand-gated ion channels) and metabotropic. Ionotropic receptors mediate rapid signalling and produce near instant changes in cellular function. Metabotropic receptors produce comparatively slow changes in cellular function,[note 1] their signalling methods are usually significantly more sophisticated and usually includes their ability to increase/reduce the production of second messengers like cyclic adenosine monophosphate (cAMP) or cyclic guanine monophosphate (cGMP). They often also have effects (both inhibitory and excitatory) on ion channels, hence affecting electrical excitability. Ionotropic receptors only exist in electrically-excitable cells as only electrically-excitable cells are susceptible to the changes in electrical excitability produced by ionotropic receptor activation. Ionotropic receptors often have significant effects on neurotransmitter release in the synaptic cleft of several neurons.
Examples of receptors include the monoamine receptors, such as the serotonin receptors (which are numbered 5-HT1-7, with a few subtypes belonging to the 5-HT1 and 5-HT2 families being alphabetized from A to F for family 1 and A to C for family 2), adrenergic receptors (that respond to adrenaline and noradrenaline; two subgroups – α1-2 (also subdivided into alphabetized subtypes) and β1-3), dopamine receptors (D1-5) and trace amine-associated receptors (only ones that exist in humans are TAAR1,2,5,6,8,9). Most monoamine receptors are metabotropic, with the following sole exception: 5-HT3 receptors.
- ↑ They are slow on a cellular level, but they are near instant, relative to how fast animals can process information, including us humans, usually
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 Blumenthal, DK; Garrison, JC (2010). "Chapter 3. Pharmacodynamics: Molecular Mechanisms of Drug Action". In Brunton, LL; Chabner, BA; Knollmann, BC. Goodman & Gilman's The Pharmacological Basis of Therapeutics, twelfth edition. AccessMedicine (New York, United States of America: McGraw Hill). Retrieved 13 September 2014.