This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Pharmacology
Which of the following is not true about the mechanism of action of digitalis? 
Select and explain. 
A. It binds to the intracellular face of Na+ K+ ATPase enzyme, B. There is rise in intracellular Na+, C. It has positive ionotropic action, D. Digitalis action is independent of cardiac innervation
A: It binds to the intracellular face of Na+ K+ ATPase enzyme
Answer: A: It binds to the intracellular face of Na+ K+ ATPase enzyme 
Explanation: Ans. is 'a' i.e., It binds to the intracellular face of Na+ K+ ATPase enzyme Digitalis mechanism of action* Digitalis increases the force of contraction by a direct action independent of the innervation.* It binds to the extracellular face of the Na+ K+ ATPase and inhibits the enzyme causing rise in the intracellular levels of Na+.* The raised Na+ in turn inhibits the Na+ Ca2+ exchanger and causes rise in intracellular Ca2+.* This raised intracellular Ca2+ is responsible for the positive ionotropic effect.* Thus, digitalis increases the cardiac contractability and force of contraction.