Total Na, K-ATPase concentration in patients with severe heart failure
[A] Increased by 50%
[B] Decreased by 40%
[C] Do not change
[D] Not detectable
- Studies show that patients with heart failure have a 40% lower concentration of total Na, K-ATPase.
- Ouabain is a cardiac glycoside that inhibits the Na+-K+ ATPase by binding to the K+ site.
- Digoxin and Digitoxin directly inhibit the Na+-K+ ATPase.
- This inhibition causes a buildup of excessive K+ extracellularly, and accumulation of excessive Na+ intracellularly as the Na+-K+ ATPase can no longer pump K+ into the cell or pump Na+ out of the cell. This buildup of intracellular Na+ hinders the concentration gradient that usually drives the Na+/Ca 2+ channel exchanger, which generally pumps Na+ into the cell and Ca 2+ out of the cell because the concentration gradient is not favorable for Na+ to enter the cell as excessive Na+ has built up intracellularly. This indirect inhibition of Na+/Ca 2+ exchange, therefore, causes a buildup of Ca 2+ intracellularly because the exchanger cannot allow Ca 2+ to exit the cell since it cannot accept Na+ into the cell. This increased intracellular Ca 2+ then increases cardiac contractility.