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A 68-year-old man recently diagnosed with heart failure, started a treatment with metoprolol, losartan, furosemide and digoxin. Which of the following molecular actions most likely mediated the positive inotropic action of digoxin?



A. Closing of calcium channels in cardiac cell membranes
B. Increased release of CA++ from sarcoplasmic reticulum during systole
C. Activation of Na+/K+ ATPase
D. Activation of CA++/Na+ exchanger in cardiac cell membranes
E. Opening of K+ channels in cardiac cell membranes
Asked by Easton, Last updated: Dec 05, 2017

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John Smith

John Smith

Answered on Sep 09, 2016

Increased release of ca++ from sarcoplasmic reticulum during systole-learning objective: explain the molecular mechanism of action digoxin.answer: bat the molecular level all cardiac glycosides inhibit na+/k+ atpase, the membrane boundtransporter called the sodium pump. the increased amount of sodium inside the cell inhibits theca++/na+ exchanger, an antiport that uses the electrochemical potential for na+ to drive ca++extrusion. the consequence of this inhibition is that less ca++ is removed from the cell. theincreased intracellular calcium is stored in the sarcoplasmic reticulum during diastole, andtherefore a greater amount of ca++ is released from the sarcoplasmic reticulum during systole.a) digitalis glycosides (at high concentration) can open, not close, cardiac calcium channels.c, d) (see explanation above)e) digitalis glycosides have no effect on potassium channels.
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