Three basic ways the Na-K-ATPase participates in signaling. 1) Na gradient established by the Na-K-ATPase is used to drive Na/Ca2 exchange by NCX, the Na/Ca2exchanger. By inhibiting the Na-K-ATPase, ouabain reduces the Na gradient and less Ca2is driven out of the cell. This is the simplest form of Ca2modulation by Na-K-ATPase activity, and recent research has revealed much more detail and regulatory complexity than suggested in the diagram. 2) Ouabain binds to the Na-K-ATPase and activates Src interacting with the pump in a signaling complex. The Na-K-ATPase can also interact with inositol 1,4,5 trisphosphate receptor (not shown). Again, much more detail is known than shown in the diagram. The activation of ERK1/2 by phosphorylation is an easily measured response to ouabain signalplex formation. 3) It is the hydrolysis of ATP by Na-K-ATPase that activates AMPK in stimulated salivary acinar cells. Activated AMPK then brings about a reduction in the phosphorylation of ERK1/2. By inhibiting the Na-KATPase, ouabain blocks this process and results in a higher level of activation of ERK1/2. Although the final result resembles the events in 2, the mechanism is different.