muscle relaxants, receptor reserve and lethal injection

there are two types of neuromuscular relaxants (that i have learned, there are probably many more). one kind inhibits your muscles from being activated but depolarization occurs, one kind depolarizaiton does not occur.

Non-depolarization: (pancuronium, tubocurarine, vecuronium, mivacurium, rocuronium) this type works by binding to the nicotinic receptors and not allowing acetylcholine to bind. this drug demonstrates competitive, reversible binding.

depolarizing drugs: (ie succinylcholine) allows the muscle cell to be depolarized, but doesn't allow the sodium channels to be reactivated, and thus you get no more muscle contraction.

receptor reserve: this is a bit of a dificult concept. a ligand (drug) binds to its specific receptor at its target tissue. sometimes, to get a maximal effect, you dont have to have a drug binding to all the receptors. so, say you have a complete effect of the drug with only 80% of the receptors bound to drug, you have a receptor reserve (receptors unbound).

drugs like non-depolarizing neuromuscular relaxants bind to the receptor and inhibit a normal physiologic action, muscle contraction. however, if enough acetylcholine is present, you can still get muscle contraction.

diferent tissues have diferent levels of receptor reserve, and for very good reason. small fine muscles (facial expression) have the lowest reserve, so they will be affected first by these drugs. large muscles (leg and trunk muscles) have medium receptor reserve, so they will be affected next. lastly comes the diaphragm (the muscule that allows you to breath). it has the highest receptor reserve, meaning it will be the last one to be affected by this drug, which interestingly enough comes from a south american plant used by indians on the tips of arrows to kill animals. so, God designed our bodies to preserve life.

lethal injection: tubocurarine, a non-depolarizing muscle relaxant with a duration of action greater than 60 min and metabolized by the liver and kidney, is used for lethal injection. it paralizes your diaphram and you sufficate. yikes!

sorry for ending on such a depressing note. on friday we started the beautiful day with a lecture on death and the process of dying. happy thoughts...