Question
The role of ion channels on vascular endothelium is:
| A. |
Ca+ influx |
| B. |
K+ efflux |
| C. |
Na+ influx |
| D. |
Cl– efflux |
Show Answer
|
Correct Answer » A Explanation |
 |
- Vascular endothelial cells regulate:
- Vascular tone
- Blood flow
- Nitric oxide (NO) production
- Endothelium-dependent vasodilation
- The most important intracellular signaling event in endothelial cells is calcium (Ca²⁺) influx through endothelial ion channels.
- Increased intracellular Ca²⁺:
- Activates calmodulin
- Stimulates endothelial nitric oxide synthase (eNOS)
- Increases nitric oxide (NO) production
- NO diffuses into vascular smooth muscle and activates guanylate cyclase
- Increased cyclic guanosine monophosphate (cGMP) causes smooth muscle relaxation and vasodilation.
Explanation of Each Option
A. Calcium (Ca²⁺) influx – Correct
- Primary signaling event in vascular endothelial cells.
- Activates eNOS via calmodulin.
- Produces nitric oxide leading to vasodilation.
- Essential for endothelium-dependent vascular relaxation.
B. Potassium (K⁺) efflux – Incorrect
- Potassium channels contribute to membrane hyperpolarization.
- They modulate endothelial function but are not the primary signaling mechanism responsible for endothelial nitric oxide production.
C. Sodium (Na⁺) influx – Incorrect
- Sodium influx has a limited role in endothelial signaling.
- It is not the principal mechanism regulating endothelial vasodilator function.
D. Chloride (Cl⁻) efflux – Incorrect
- Chloride channels help regulate cell volume and membrane potential.
- They are not the major ion movement responsible for endothelial nitric oxide synthesis.
