🔋 The Sodium-Potassium Pump (Na⁺/K⁺-ATPase)
The Na/K pump is the battery of the cell. It maintains the resting membrane potential and powers the sodium-calcium exchanger (NCX) that keeps calcium out of the cell.
⚡ The Pump's Action: Uses 1 ATP to pump 3 Na⁺ OUT and 2 K⁺ IN. This creates a negative resting potential (-70 mV) and a steep sodium gradient.
Link to Vascular Tone
Pathway 1: The Sodium-Calcium Exchanger (NCX)
- NCX uses the Na⁺ gradient to pump Ca²⁺ OUT of the cell.
- If the Na/K pump fails, Na⁺ builds up inside, the NCX reverses, and Ca²⁺ floods IN → Constriction.
Pathway 2: Membrane Potential
- The pump keeps the cell at -70 mV. If it slows down, the cell depolarizes.
- Depolarization opens Voltage-Gated Calcium Channels (VGCC) → Calcium influx → Constriction.
Clinical Implications
| Condition / Drug | Effect on Na/K Pump | Result on BP |
|---|---|---|
| High Salt Diet | Overworked, cannot keep up (Na⁺ builds up). | ⬆ Increases BP (Vasoconstriction) |
| Thiazide Diuretics | Reduces serum Na⁺, allowing the pump to recover. | ⬇ Lowers BP (Vasodilation) |
| Digoxin (Therapeutic) | Inhibits pump in heart → increases Ca²⁺ in heart (stronger squeeze). | Treats Heart Failure |
| Digoxin Overdose | Inhibits pump in vessels → Na⁺ builds up → Ca²⁺ influx. | ⬆ Dangerously High BP (Vasoconstriction) |
Physiological Takeaway: The Na/K pump is why we recommend low-salt diets and use diuretics. By reducing the sodium load, we let the pump restore the membrane potential, shut the calcium channels, and relax the vessels.