Biochemistry · Enzyme
Na⁺/K⁺-ATPase (sodium pump) !
The sodium pump spends ATP to push Na⁺ out of the cell and bring K⁺ in. Digoxin blocks it in the heart.
Updated 2026-11-01
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Key facts
- Each ATP moves 3 Na⁺ out and 2 K⁺ in, against both gradients.
- A P-type ATPase: during each cycle it is briefly phosphorylated (states such as E2P) while it changes shape.
- The gradients it builds keep the membrane potential and the ion balance of the cell.
- It sits in the plasma membrane, on the basolateral side in epithelia.
Structure
- Catalytic α subunit (ATP1A1 is the isoform found in most cells), plus a β subunit and an FXYD regulator.
- Structure 4RET is the pig kidney pump in the E2P state with digoxin bound on its outer face.
Regulation
- The α/β/FXYD combination in each tissue tunes how the pump behaves.
- Phosphorylation by kinases (PKA among them) and dephosphorylation adjust its activity.
Inhibitors and toxins
- Cardiac glycosides (digoxin): bind the outer face and block the pump.
- Ouabain and digitoxin, other cardiac glycosides.
Clinical notes
- In heart muscle, less pumping leaves more Na⁺ inside; the Na⁺/Ca²⁺ exchanger then removes less Ca²⁺, so contraction gets stronger.
- Digoxin also boosts vagal tone, slowing the AV node: used in heart failure and to control rate in atrial fibrillation.
- Low potassium, low magnesium, high calcium and poor kidney function raise the risk of digoxin toxicity.
- ATP1A1 variants cause a hereditary axonal neuropathy and a syndrome with low magnesium and seizures.
Drugs that act here
Related conditions
Related
Test yourself
Think of the answer, then tap the question to see it.
How many Na⁺ and K⁺ does the pump move per ATP?
3 Na⁺ out and 2 K⁺ in.
How does blocking the pump make the heart beat harder?
More Na⁺ stays inside, the Na⁺/Ca²⁺ exchanger expels less Ca²⁺, and more Ca²⁺ is available for contraction.
Which findings raise the risk of digoxin toxicity?
Low potassium, low magnesium, high calcium and reduced kidney function.
Which subunits make up the sodium pump?
A catalytic α subunit, a β subunit and an FXYD regulatory subunit.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: ATP1A1: Sodium/potassium-transporting ATPase subunit alpha-1 (human) (UniProt, 2026); 4RET: Crystal structure of the Na,K-ATPase E2P-digoxin complex with bound magnesium (RCSB Protein Data Bank, 2026); DIGOXIN tablet (DailyMed, US National Library of Medicine, 2026); Digoxin: MedlinePlus Drug Information (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.