<prompt> Which of the following is not true about the mechanism of action of digitalis?It binds to the intracellular face of Na K ATPase enzymeThere is rise in intracellular NaIt has positive ionotropic actionDigitalis action is independent of cardiac innervation  <response>: 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. 