Final answer:
After the Na⁺-K⁺ ATPase hydrolyzes ATP, the extracellular sodium ion concentration increases and the intracellular potassium ion concentration increases, as sodium ions are expelled from the cell and potassium ions are taken in.
Step-by-step explanation:
Immediately after the Na+-K+ ATPase protein hydrolyzes ATP, several events occur in succession as part of the sodium-potassium pump's function. The hydrolysis of ATP results in the phosphorylation of the pump, leading to a conformational change. During this change, the pump binds three Na+ ions intracellularly (inside the cell). These Na+ ions are then released into the extracellular space (outside the cell) causing another allosteric change.
This is followed by the binding of two K+ ions from the extracellular space. Subsequently, the phosphate group previously attached is released, triggering the pump to return to its original conformation and release the K+ ions into the cytosol (intracellular fluid). Therefore, the extracellular sodium ion concentration increases and the intracellular potassium ion concentration increases as direct consequences of the ATP hydrolysis by the Na+-K+ pump.
Through this activity, the pump actively transports Na+ out of and K+ into the cell against their respective concentration gradients, maintaining essential cellular functions such as the resting membrane potential and overall ion balance within the cell.