G Protien Coupled Receptors

Human lore has recognized since prehistory that many substances cause pharmacological or medicinal effects when introduced into the body. A large variety of responses occur: some are beneficial, others are not. The goal of modern pharmacology is to understand how drugs work and to discover or design new drugs with optimal therapeutic value but minimal undesirable or toxic side-effects.

It was not discovered until the late 19th century that many drugs function by interacting with macromolecular structures within an organism that are known as receptors. Many different types of receptors have been identified. A given type will only respond to a certain group of chemical substances, and the response can vary both in function and intensity. Each receptor type has normal functions that are activated by chemicals that occur naturally within the body. These are called endogenous substances. Drugs are exogenous chemicals that can act like the endogenous ones, though sometimes they are used to block normal receptor behavior.

G Protein Coupled Receptors (GPCRs, also known as Serpentine Receptors) are plasma membrane proteins that span the membrane seven times. These receptors act by regulating the activity of a group of intracellular proteins known as G proteins. GPCRs facilitate the binding of guanosine triphosphate (GTP) to specific G proteins, which in turn regulates the activity of an intracellular effector system.

Receptors are usually named after natural substances that are known to act upon them, as in the three types shown below.

Courtesy: Dr. Edward J. Bertaccini (Stanford University)
OPIOID RECEPTORS

Opium is the Greek word for juice, the drug being obtained from the juice of the opium poppy (Papaver somniferum). Opium contains over 20 distinct alkaloids. In 1806, Sertürner isolated the first pure substance from opium that he named morphine, after Morpheus, the Greek god of dreams. Endogenous opioids and opioid receptors have been identified. Three distinct receptors have been cloned (mu, delta, & kappa).


Courtesy: NIDA

Morphine
MUSCARINIC CHOLINERGIC RECEPTORS

The mushroom Amanita muscaria is the source from which the alkaloid muscarine was first isolated. Some of the toxic effects of ingesting this mushroom are associated with its action on the muscarinic receptors in the central nervous system. Muscarinic cholinergic receptors were named based on their sensitivity to muscarine by Sir Henry Dale in 1914. Five subtypes of muscarinic receptors have been cloned (M1-M5).


© Copyright Nathan Wilson 1994

Muscarine
CANNABINOID RECEPTORS

Cannabis (Cannabis sativa) has been cultivated for centuries both for the production of hemp fiber and for its medicinal and psychoactive properties. 61 different cannabinoids have been identified in the smoke of cannabis. One of these, Delta-9- Tetrahydrocannabinol, produces most of the characteristic pharmacological effects. Cannabinoid receptors have been identified in the brain and immune system. Two distinct cannabinoid receptors have been cloned (CB1 & CB2).

 
Delta-9-Tetrahydrocannabinol

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Updated 13 March 2002