CVS Practice Test

What is the primary effect of the Na+/K+ ATPase pump on intracellular calcium levels?

1. Decreases intracellular calcium

2. Increases intracellular calcium

3. Has no effect on calcium

4. Induces calcium storage

The correct answer is: Increases intracellular calcium

The Na+/K+ ATPase pump primarily functions to maintain the electrochemical gradient across the cell membrane by actively transporting sodium out of the cell and potassium into the cell. While its primary role focuses on sodium and potassium ions, it indirectly influences intracellular calcium levels as well. When the Na+/K+ ATPase pump works effectively, it helps to lower the intracellular sodium concentration. Since there is less sodium inside the cell, the sodium-calcium exchanger (NCX), which operates based on the sodium gradient, can function more efficiently. The NCX usually extrudes calcium from the cell in exchange for sodium. When intracellular sodium levels decrease due to the action of the Na+/K+ ATPase pump, the NCX can take in less sodium and consequently expel more calcium from the cell, thus reducing intracellular calcium levels. Therefore, while the Na+/K+ ATPase pump does not directly transport calcium, its activity leads to a reduction in intracellular calcium concentration through the enhanced function of the sodium-calcium exchanger. The primary effect of the Na+/K+ ATPase pump is to decrease intracellular calcium levels as part of its broader role in regulating cellular ion concentrations and maintaining homeostasis.