This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hypeension, Arrhythmias, Dyslipidemia, Subject name: Pharmacology
A drug effect that is produced by therapeutic doses of both timolol and amiodarone is blockade of: 
Select and explain. 
A. Cardiac Na+ channels, B. Cardiac K+ channels, C. Beta adrenoceptors, D. Alpha-adrenoceptors
C: Beta adrenoceptors
Answer: C: Beta adrenoceptors 
Explanation: Amiodarone has wide spectrum of antiarrhythmic actions. It acts by all the four mechanisms: blockade of Na+ channels blockade of b receptors blockade of K+ channels blockade of Ca2+channels. Timolol is a b blocker. Therefore, common action of these two drugs is inhibition of b-receptors.