Digoxin increases myocardial contractility primarily through which intracellular mechanism?
- A Inhibition of sarcolemmal Na+-K+ ATPase leading to reduced Na+ gradient and decreased Ca2+ extrusion by NCX ✓
- B Direct opening of L-type calcium channels in the sarcolemma
- C Inhibition of phosphodiesterase type 3 with increased cAMP
- D Enhanced reuptake of calcium into the sarcoplasmic reticulum via SERCA
Correct answer: A. Inhibition of sarcolemmal Na+-K+ ATPase leading to reduced Na+ gradient and decreased Ca2+ extrusion by NCX
Explanation
Digoxin inhibits the sarcolemmal Na+-K+ ATPase, raising intracellular Na+. The smaller Na+ gradient reduces calcium extrusion through the Na+-Ca2+ exchanger (NCX), so more Ca2+ remains in the cytosol and is loaded into the sarcoplasmic reticulum, increasing calcium release on each beat. Option C describes milrinone, and option D describes the mechanism by which beta agonists accelerate relaxation, neither of which applies to digitalis.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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