Question

The concentration of free Ca₂⁺ in the cytosol of an unstimulated cell is kept low compared with its concentration in both the extracellular fluid and the endoplasmic reticulum. Which of the following help to maintain this difference?

1) Ca₂⁺ pumps in the plasma membrane
2) Ca₂⁺ pumps in the ER membrane
3) Ca₂⁺ channels in the ER membrane
4) Ca₂⁺ channels in the plasma membrane

Answer 1

Ca²⁺ pumps and channels in the plasma membrane and endoplasmic reticulum help maintain the low concentration of Ca²⁺ ions in the cytosol of unstimulated cells.

Step-by-step explanation:

The concentration of free Ca²⁺ in the cytosol of an unstimulated cell is kept low compared with its concentration in both the extracellular fluid and the endoplasmic reticulum mainly due to the presence of Ca²⁺ pumps in the plasma membrane and in the endoplasmic reticulum membrane. These pumps actively remove Ca²⁺ ions from the cytosol and transport them out of the cell or into the endoplasmic reticulum. The presence of Ca²⁺ channels in the plasma membrane and in the endoplasmic reticulum membrane also helps to maintain this difference as they allow the influx of Ca²⁺ ions into the cytoplasm only when there is a signaling event.