– please help me understand the basics of pharmacology receptors/drug mechanisms


I understand the kinetics and clearance and stuff, but I can’t wrap my head around how to tell what drug goes with what receptor and what it does when it gets there… What does it mean if something is described as muscarinic, nicotinic, adrenergic, or cholinergic? What is a catecholamine? Other than their physical location, is there any difference between alpha/beta/N/M receptors?

I’ve read books, looked at diagrams, watched videos, gone to lectures, and tried asking my profs but I still don’t understand and I’m going crazy because I always miss the pharm questions on my exams…

In: 3

There are a group of closely related proteins that were discovered because they can be activated by the toxin muscarine. Similarly there are a group of proteins that were discovered because they are activated by the toxin nicotine. They were therefore named after the activating compound. That is the convention for most receptors. They are classified by the chemical that was used to discover them. In actuality both of these receptor families are activated by acetylcholine, which is the definition of a cholinergic receptor.

Similarly if a receptor is activated by a catecholamine like dopamine, epinephrine, or norepinephrine it is called catecholinergic.

Catecholamines are a handful of different molecules with a similar structure in the same pathway of synthesis (you make dopamine, which you can turn into norepinephrine, which you can turn into epinephrine.) We group them together because they’re closely related and have overlapping functions.

Think of the different receptors as different types of buttons you can push to send different messages. Each of them will have a different shape, which determines which molecules can push it. To your question, yes, alpha receptors are shaped different than beta receptors, and an alpha-1 receptor is shaped different than an alpha-2 receptor; this means that different catecholamines may prefer one to another. Alpha and beta receptors are also located in different places.

A cholinergic receptor binds acetylcholine. Muscarinic and nicotinic are two different types of cholinergic receptors that show up in different places. This is part of what gets confusing: Acetylcholine is one messenger chemical, but it can have very different effects at different places. Other chemicals can also affect this receptor, like nicotine at the nicotinic receptor or a bunch of drugs that block the muscarinic receptor.

An adrenergic receptor binds norepinephrine and epinephrine. Alpha and beta receptors are different types of adrenergic receptors. Likewise, they show up different places and thus have different effects.

muscarinic, nicotinic, adrenergic, or cholinergic receptors are named after the drugs or toxins that act on them

So there’s a toxin called muscarine. which comes from certain mushrooms. scientists found the receptor it targets, and they called it the muscarinic receptor.
Same deal with nicotine, from tobacco. It targets a different receptor, so they called that one the nicotinic receptor.
adrenergic is stimulated by adrenaline (epinephrine)
cholinergic are stimulated by acetylcholine (a neurotransmitter).