Digoxin exerts its positive inotropic effect in heart failure by inhibiting the sarcolemmal Na+/K+ ATPase pump. The downstream increase in intracellular calcium is mediated by which transporter?

• A L-type calcium channel
• B Ryanodine receptor on sarcoplasmic reticulum
• C Sarcoplasmic reticulum Ca2+ ATPase (SERCA)
• D Na+/Ca2+ exchanger (NCX) operating in reverse mode ✓

Explanation

Na+/K+ ATPase inhibition raises intracellular sodium, reducing the sodium gradient that drives the Na+/Ca2+ exchanger. This causes NCX to operate in reverse (or forward mode slows), increasing intracellular calcium available for contraction. The L-type channel triggers calcium release; ryanodine receptors and SERCA handle SR calcium handling but are not the primary link between Na+/K+ ATPase inhibition and inotropy.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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