Copyright e The McGraw-Hill Companies, Inc. Permission required for reproduction or displ Extracellular fluid Intracellular fluid Nat 15 mM Nat 150 mM K+ 150 mM K+5 mM ATP nAt 2K+ ADP. Here, in the operation of the Na*-K-ATPase, also known as the"sodium pump, each ATP hydrolysis moves three sodium ions out of, and two potassium ions into, the cellHere, in the operation of the Na+ -K+ -ATPase, also known as the “sodium pump,” each ATP hydrolysis moves three sodium ions out of, and two potassium ions into, the cell