The positive inotropic effect of digitalis due to inhibition of the Na+/K+ ATPase pump in cardiac muscle cell membrane leads to:
Digitalis selectively binds to the extracellular face of membrane- Na-k ATPase is inhibited. Inhibition of this cation pump results in progressive accumulation of Na intracellularly. Indirectly result in intracellular Calcium accumulation. REF.Essentials of medical pharmacology K D TRIPATHI 6 Edition)
Decreased activity of Na+/Ca++ exchanger causing decreased influx of sodium and decreased efflux of Ca++ in the sarcolemma
Decreased efflux of Na+ leading to less negative resting membrane potential and opening of voltage gated Ca++ channels on the T tubules
Increased intracellular Na+ causing increased efflux of Na+ and increased influx of Ca++ through Na+/ Ca++ exchanger in the sarcolemma
Increased intracellular Na+ decreasing the activity of Ca++ pump in the sarcoplasmic reticulum
Cardiovascular system