China
Africa
Explore chapters and articles related to this topic
Receptors 1
Published in James E. Ferrell, Systems Biology of Cell Signaling, 2021
Note that this model can explain why many receptors, including the β2-adrenergic receptor, exhibit basal activity, and it explains the existence of inverse agonists; in the context of this model, an inverse agonist is a drug that binds better to the inactive conformation than to the active conformation. In fact the structure of the inactive conformation of the receptor shown in Figure 2.1b was obtained in the presence of an inverse agonist, the drug carazolol. The ligand evidently firms up the positions of the transmembrane helices, and without such a ligand, only structures of the lower portions of the helices are obtained. Carazolol not only blocks the effects of agonists like epinephrine on receptors and cells, it also decreases the basal levels of β2-adrenergic receptor signaling seen in cells by binding more strongly to the inactive receptor than to the active receptor. In this way, inverse agonists select the receptor’s inactive conformation, whereas agonists select the active conformation.
The Neuromuscular Junction
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Agonists of a given neurotransmitter are substances that bind to the receptor of the neurotransmitter and mimic its action. There are many ACh agonists that bind to ACh receptors and depolarize the endplate. Generally, however, they do not have the same kinetics as ACh, do not desensitize the channel in the same manner, and are not similarly affected by AChE. In low doses, they mimic the action of ACh, but in high doses, or with prolonged application, they initially cause muscular contraction followed by desensitization, accommodation, and eventual neuromuscular block. Because of this, they are termed depolarizing blocking agents. Examples of ACh agonists are nicotine, succinylcholine, and decamethonium. Succinlycholine is applied intravenously during surgery as a short-acting muscle relaxant. It has a rapid onset of about 30 s and a duration of action of 5–10 minutes. It is not hydrolyzed by AChE but by other cholinesterases normally found in the blood.
Plant pharmacology: Insights into in-planta kinetic and dynamic processes of xenobiotics
Published in Critical Reviews in Environmental Science and Technology, 2022
Tomer Malchi, Sara Eyal, Henryk Czosnek, Moshe Shenker, Benny Chefetz
Drugs generally do not create a new effect, but rather, activate or inhibit a specific receptor-related activity. Receptors are sites to which specific ligands bind, thereby altering the cell's biochemical activity. An agonist binds to a receptor and activates a sequence of events that leads to a response. An antagonist binds to a receptor to inhibit the action, without initiating any effect itself. Drugs conferring a short duration of receptor activation generally interact via weaker bonds (ionic, hydrogen or van der Waals), whereas long-duration or irreversible drug–receptor interactions may form stronger bonds, such as covalent bonds. A drug’s ability to affect a specific receptor is related to its affinity and efficacy, which are parameters determined by its chemical structure. Affinity is defined as the probability of a drug occupying its target receptor upon interaction. Efficacy is defined as the extent to which a drug activates a receptor, resulting in a cellular response also known as drug effect (Buxton & Benet, 2013; Page & Maddison, 2008; Raj & Raveendran, 2019).
Human exposure to synthetic endocrine disrupting chemicals (S-EDCs) is generally negligible as compared to natural compounds with higher or comparable endocrine activity. How to evaluate the risk of the S-EDCs?
Published in Journal of Toxicology and Environmental Health, Part A, 2020
Herman Autrup, Frank A. Barile, Sir Colin Berry, Bas J. Blaauboer, Alan Boobis, Herrmann Bolt, Christopher J. Borgert, Wolfgang Dekant, Daniel Dietrich, Jose L. Domingo, Gio Batta Gori, Helmut Greim, Jan Hengstler, Sam Kacew, Hans Marquardt, Olavi Pelkonen, Kai Savolainen, Pat Heslop-Harrison, Nico P. Vermeulen
Receptors are cellular components that bind molecules of diverse chemical structures. Known as ligands, these molecules activate or inhibit the receptor function and thereby elicit a physiological response. Ligands that activate a response are agonists; those that block the response are antagonists. Potency of the EDs depends on the strength of interaction of their ligand molecules with a specific receptor or enzyme.