Digoxin’s inotropic effect results from inhibition of Na+/K+ ATPase.

Digoxin’s inotropic effect results from inhibition of Na+/K+ ATPase.

• A. True
• B. False
• C. Not sure
• D. It depends

Answer: (A)

Digoxin increases heart muscle contractility by blocking the Na+/K+ ATPase pump on cardiac myocytes. When this pump is inhibited, intracellular sodium rises. The elevated Na+ reduces the driving force for the Na+/Ca2+ exchanger, leading to less calcium being pumped out of the cell. Calcium then accumulates inside the cell, boosting calcium availability for contraction. This extra intracellular calcium enhances cross-bridge cycling and strengthens each heartbeat, producing a positive inotropic effect. While digoxin also has vagal effects that can slow conduction, these are separate from its inotropic mechanism. So the statement is true.

Digoxin increases heart muscle contractility by blocking the Na+/K+ ATPase pump on cardiac myocytes. When this pump is inhibited, intracellular sodium rises. The elevated Na+ reduces the driving force for the Na+/Ca2+ exchanger, leading to less calcium being pumped out of the cell. Calcium then accumulates inside the cell, boosting calcium availability for contraction. This extra intracellular calcium enhances cross-bridge cycling and strengthens each heartbeat, producing a positive inotropic effect. While digoxin also has vagal effects that can slow conduction, these are separate from its inotropic mechanism. So the statement is true.