Question

5. Patient with chronic heart failure is using digoxin (digitalis) for more than 1 year. Describe what effect has this treatment with digitalis have on the distribution of ions across the membrane of cardiac muscle cells? How digitalis helps to treat patients with heart failure?

Answer 1

Digitalis, also called as digoxin or oubain is given to a person who has symptoms of chronic heart failure. It helps the weakened heart to pump the blood more effectively by improving the force of heart muscle contraction and restores the normal and steady heart rythm.

In the myocardium, the action of digitalis causes inhibition of Na⁺/K⁺ ATPase by binding to its extracellular part. The role of Na⁺/K⁺ ATPase is to keep the level of sodiumlow inside the cell by pumping three Na⁺ outof the cell for two K⁺ that are pumped in. The inhibition of Na⁺/K⁺ ATPase by digitalis increases the sodium levels inside the cell which in turn reduces the activity of Na⁺/Ca²⁺ exchanger which otherwise imports three Na⁺ into the cell in exchange of one calcium ion which is exported out of the cell. The overall result is the increase in cellular calcium levels that are stored by cells in sarcoplasmic reticulum. During action potential, there is an increased release of calcium which leads to increased contractibility or force of contraction of heart. In addition, increased intracellular calcium stretches the Phase 4 and Phase 0 of action potential leading to the decreased heart rate. This improves or relieves the patient from the symptoms of heart failure.