This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
Tetraethyl ammonium acts by blocking which of the following channels? 
Select and explain. 
A. Na+, B. Cl-, C. K+, D. Ca
C: K+
Answer: C: K+ 
Explanation: C i.e. K+Ref: 12th edition, page 272Explanation:TetraethylammoniumGanglionic blocker which blocks voltage-gated K+ channels.Tried previously for treatment of Phantom Limb.Marshall first described the "nicotine-paralyzing" action of Tetraethylammonium (TEA) on ganglia in 1913.TEA was largely overlooked until the effects of the ion on the cardiovascular system and autonomic ganglia were analyzed.It is of historical importance only.