This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney, Subject name: Pharmacology
Amiloride differs from spironolactone in that: 
Select and explain. 
A. It has greater natriuretic action, B. Its diuretic action is more in the presence of conditions with elevated aldosterone levels, C. It acts from the luminal membrane side of the collecting duct cells, D. It can cause hypokalemia on long term use
C: It acts from the luminal membrane side of the collecting duct cells
Answer: C: It acts from the luminal membrane side of the collecting duct cells 
Explanation: Amiloride is a K+ sparing diuretic and like other diuretics, act from luminal membrane side. On the other hand, Spironolactone does not require access to tubular lumen for action. Diuretic action of both amiloride and spironolactone is quite feeble. Due to its aldosterone receptor blocking action, spironolactone is more effective in the presence of conditions with elevated levels of aldosterone (like CHF). Both of these diuretics can cause hyperkalemia when used with K+ supplements or ACE inhibitors.