Cardiac Glycosides

Question 1

What are cardiac glycosides?

Answer 1

• organic compounds (carbon backbone)
• able to increase inotropic contraction force

Question 2

What are cardiac glycosides used for?

Answer 2

• atrial fibrillation and flutter
• heart failure

Question 3

What is the most common drug used as a cardiac glycoside?

Answer 3

• digoxin

Question 4

What is the mechanism of action of digoxin, a cardiac glycoside?

Answer 4

• inhibits the enzyme ATPase
• stop N+ / K+ ATPase pump
• Na+ ⬆️ inside the cell
• Na+ leaves via Na+ / Ca2+ exchanger and Ca2+ ⬆️ inside the cell

Question 5

Why is N+ / K+ ATPase so important in cells?

Answer 5

• maintains resting membrane potential
• maintain electrochemical charge

Question 6

In normal physiology in cardiomyocytes what does the N+ / K+ ATPase use to move cations against concentrations gradients and what moves into the cell and what moves outside the cell?

Answer 6

• ATP used
• Na+ moves out of cell (3)
• K+ moves into cell (2)

Question 7

What is ATPase?

Answer 7

• enzyme inside cells
• hydrolyses ATP to ADP

Question 8

If Na+ / K+ ATPase is working normally what happens to the cell?

Answer 8

• 3 Na+ leave and 2 K+ enter the cell

Question 9

How does inhibiting N+ / K+ ATPase increase inotropic force?

Answer 9

• Na+ remains in cell
• Na+ can leave through Na+ / Ca2+ exchanger
• Na+ leaves and Ca2+ enters

Question 10

In addition to inhibiting N+ / K+ ATPase and increasing intracellular Ca2+, what other mechanism is digoxin able to work through?

Answer 10

• stimulates the vagus nerve (parasympathetic)
• reduced HR through SA and AV node

Question 11

Why can digoxin, a cardiac glycoside be useful in treating chronic heart failure (CHF) patients?

Answer 11

• CHF means heart is weakened
• digoxin ⬆️ inotropic force