Question

The positive inotropic effect of digitalis is due to inhibition of $Na^+/K^+$ ATPase pump in cardiac muscle cell membrane leading to

• A. Decreased activity of $Na^+/Ca^{++}$ exchanger causing decreased influx of $Na^+$ and decreased efflux of $Ca^{++}$ in the sarcolemma
• B. Decreased efflux of $Na^+$ leading to less negative resting membrane potential and opening of voltage gated $Ca^{++}$ channels on the T tubules
• C. Increased intracellular $Na^+$ causing increased efflux of $Na^+$ and increased influx of $Ca^{++}$ through $Na^+/Ca^{++}$ exchanger in the sarcolemma
• D. Increased intracellular $Na^+$ decreasing the activity of $Ca^{++}$ pump in the sarcoplasmic reticulum

Hint:

Remember the cascade: Inhibition of $Na^+/K^+$ ATPase $\rightarrow$ Increased intracellular $Na^+$ $\rightarrow$ Decreased activity of $Na^+/Ca^{++}$ exchanger $\rightarrow$ Decreased $Ca^{++}$ efflux $\rightarrow$ Increased intracellular $Ca^{++}$ $\rightarrow$ Positive inotropy.

Answer 1

The Correct Option is A