**Question:** All of the following are true regarding diuretics except: March 2008

A. Diuretics increase intracellular sodium concentration
B. Diuretics increase intracellular calcium concentration
C. Diuretics decrease intracellular calcium concentration
D. Diuretics increase intracellular potassium concentration

**Core Concept:** Diuretics are medications that increase the excretion of water and electrolytes, particularly sodium and chloride, from the kidneys into the urine. They are commonly used to treat conditions such as congestive heart failure, edema, and hypertension. Diuretics work through various mechanisms, but the most common effect is to inhibit the sodium-potassium-2 chloride cotransporter (NKCC2) in the thick ascending limb of Henle's loop in the nephron, leading to an increase in urine production and fluid excretion.

**Why the Correct Answer is Right:**

C. Diuretics decrease intracellular calcium concentration (Option C) is the correct answer because diuretics primarily affect the tubular reabsorption of electrolytes, not the intracellular levels. Calcium reabsorption occurs primarily in the distal convoluted tubule and the collecting duct, where calcium channels and transporters are involved, rather than the thick ascending limb or the nephron cells where diuretics act. These medications do not directly impact intracellular calcium levels.

**Why Each Wrong Option is Incorrect:**

A. Diuretics increase intracellular sodium concentration (Option A): While diuretics do increase urinary sodium excretion, they actually increase sodium reabsorption in the distal convoluted tubule and the collecting duct, leading to increased osmotic diuresis and natriuresis. This results in a net loss of sodium in the urine.

B. Diuretics increase intracellular potassium concentration (Option B): Diuretics can cause a transient increase in serum potassium levels due to increased potassium excretion, but they do not directly affect intracellular potassium concentrations.

D. Diuretics decrease intracellular potassium concentration (Option D): Similar to option A, diuretics increase renal potassium excretion, which can lead to a transient increase in serum potassium levels. However, intracellular potassium levels remain unaffected by diuretic therapy.

**Clinical Pearl:** Diuretic medications primarily target the renal tubules to modulate electrolyte reabsorption, affecting serum electrolyte levels but not intracellular concentrations within the nephron cells.