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
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.