Question

You have generated antibodies that recognize the extracellular domain of the Ca2+ pump. Adding these antibodies to animal cells blocks the active transport of Ca2+ from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+?

(a) Ca2+ pumps in vesicles membranes keep cystosolic calcium levels low.
(b) Ca2+ pumps in the ER membrane keep cystosolic calcium levels low.
(c) Ca2+ pumps in the Golgi apparatus keep cystosolic calcium levels low.
(d) Ca2+ concentrations in the cytosol increase at a steady rate.

Answer 1

The presence of antibodies that block Ca2+ pumps on the plasma membrane would lead to an increase in cytosolic Ca2+ concentration, as the primary system for removing Ca2+ would be inhibited. The correct option is d.

Step-by-step explanation:

The student has asked what is expected to be observed with respect to intracellular Ca2+ concentrations when antibodies are used to block the active transport of Ca2+ from the cytosol into the extracellular environment.

In this scenario, because antibodies are blocking the calcium pumps on the plasma membrane which normally pump Ca2+ out of the cell, one can expect that the intracellular concentrations of Ca2+ would rise.

This is because the normal mechanism for maintaining low cytosolic Ca2+ levels, which involves pumping Ca2+ out of the cell, is inhibited.

Additional systems do exist within the cell to manage Ca2+ levels, such as Ca2+ pumps in the endoplasmic reticulum and the sarcoplasmic reticulum that can store Ca2+, as well as other mechanisms including endocytosis.

However, these are not the primary means of reducing cytosolic Ca2+ levels. Endocytosis is a form of active transport that can ingest material into the cell, but it does not directly relate to Ca2+ ion transport.

The most correct answer to the student's question would therefore be (d) Ca2+ concentrations in the cytosol increase at a steady rate.