<prompt> In terms of the ability of drugs like digoxin to increase cardiac contractility, their primary action on cardiac cells isactivation of adenylyl cyclaseinactivation of Na channelsactivation of the slow Ca channelinhibition of NaK-ATPase  <response>: Cardiac glycosides increase contractility by inhibiting the NaK-ATPase pump, causing an increase in intracellular Na. This, in turn, increases intracellular Ca by slowing down NaCa exchange. The increase in intracellular Ca leads to its binding to the troponin-tropomyosin complex, causing an allosteric change and facilitating the interaction between actin and myosin. 