Question

Which of the following drugs produces vascular smooth muscle relaxation primarily by opening potassium channels, leading to membrane hyperpolarization?

• A. Fenoldopam
• B. Nitroprusside
• C. Minoxidil
• D. Verapamil

Hint:

Vasodilators relax blood vessels through several different mechanisms. One important class works by opening ATP-sensitive potassium (K + ) channels in the vascular smooth muscle.

Answer 1

The Correct Option is C

Step 1: What is the question asking?
We need to identify which drug relaxes vascular smooth muscle specifically by opening potassium (K⁺) channels, leading to hyperpolarization of the cell membrane.

Step 2: What happens when K⁺ channels open?
When K⁺ channels open, potassium ions flow out of the cell (down their concentration gradient). This makes the inside of the cell more negative, a state called hyperpolarization. A hyperpolarized membrane cannot respond to signals that cause contraction, so the smooth muscle relaxes and blood vessels dilate.

Step 3: Evaluate Option 3 - Minoxidil.
Minoxidil (its active metabolite minoxidil sulfate) is a classic example of a potassium channel opener (specifically ATP-sensitive K⁺ channels). It causes hyperpolarization and vasodilation. Used as an antihypertensive and famous for hair regrowth. This is the correct answer.

Step 4: Evaluate Option 1 - Fenoldopam.
Fenoldopam is a selective dopamine D₁ receptor agonist. It causes vasodilation by increasing cAMP, not by opening K⁺ channels.

Step 5: Evaluate Option 2 - Nitroprusside.
Sodium nitroprusside releases nitric oxide (NO), which activates guanylyl cyclase, increases cGMP, and causes smooth muscle relaxation. It does not act on K⁺ channels.

Step 6: Evaluate Option 4 - Verapamil and Conclusion.
Verapamil is a calcium channel blocker (L-type). It blocks Ca²⁺ entry, not opens K⁺ channels. Among all choices, only Minoxidil works by opening K⁺ channels causing membrane hyperpolarization.
Answer: Option (3) — Minoxidil