At this point, you may be thinking, “how on earth did anyone figure out this stuff?” To answer this question you need to understand that scientists who study physiological processes often employ drugs. Yep, drugs! A drug that has the same effect as acetylcholine will result in all kinds of information about how something works. We use the terms agonist and antagonist when referring to drugs. A drug that has the same effect as the neurotransmitter (acetylcholine) would be considered an agonist. A drug that blocks the effect of the neurotransmitter is called an antagonist.
Agonists and AntagonistsAgonist & Antagonist. Author: Dolleyj Site: https://commons.wikimedia.org/wiki/File:Agonist_%26_Antagonist.jpgLicense: CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons.
Look at the table below of different drugs used in the study of muscle physiology and see if you can predict the effect the drug would have on a muscle.
Class of Drug
Example
Method of Action
Result on muscle?
Neuromuscular blocker
tubocurarine (chemical obtained from the bark of a South American plant, used as arrow poison); alpha bungarotoxin (snake poison), pancuronium (lethal injection drug)
Acetylcholine receptor antagonist
Flaccid paralysis
Neuromuscular blocker
Succinylcholine (a synthesized chemical, known as the “perfect poison” for murder)
Acetylcholine receptor antagonist (initial depolarization but then blocks the receptor)
Flaccid paralysis
Neuromuscular junction
Neostigmine (a synthesized chemical)
Inhibits Acetylcholinesterase activity
Spastic paralysis
Contractility
Salbutamol (a synthesized chemical also known as albuterol)
Enhances SERCA pump activity
Reduced contractility
Contractility
Caffeine (chemical found in seeds, nuts or leaves, used as an insecticide by the plants)
Enhances Ca2+ release at the sarcoplasmic reticulum
