True statements regarding Depolarizing muscle relaxant are all EXCEPT: March 2013 (a)
**Core Concept**
Depolarizing muscle relaxants, such as succinylcholine, work by mimicking the action of acetylcholine at the neuromuscular junction, leading to sustained depolarization of the muscle cell membrane. This results in muscle contraction (fasciculation) and ultimately, paralysis.
**Why the Correct Answer is Right**
Option C is incorrect because depolarizing muscle relaxants, unlike non-depolarizing agents, cannot be reversed by neostigmine. Neostigmine works by inhibiting acetylcholinesterase, thereby increasing acetylcholine concentrations and overcoming non-depolarizing blockade. However, since depolarizing agents directly activate the muscle cell membrane, neostigmine has no effect on reversing their action.
**Why Each Wrong Option is Incorrect**
**Option A:** Depolarizing muscle relaxants indeed cause muscle fasciculation due to the initial depolarization of the muscle cell membrane, which leads to muscle contraction.
**Option B:** Depolarizing muscle relaxants exhibit fade upon repeated stimulation, similar to non-depolarizing agents. This is because the muscle cell membrane is gradually becoming desensitized to the depolarizing agent.
**Option D:** Depolarizing muscle relaxants do exhibit post-tetanic facilitation, where the muscle responds more forcefully to tetanic stimulation after the initial depolarization. This is due to the increased sensitivity of the muscle cell membrane to subsequent stimuli.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that depolarizing muscle relaxants, such as succinylcholine, can cause severe hyperkalemia, especially in patients with muscle damage or burns. This is because depolarization of muscle cell membranes releases potassium ions into the bloodstream.
**✓ Correct Answer: C. Reversed by neostigmine**