Question

A rapid mechanism is thought to govern the localization of AQP5 in response to changes in extracellular osmolarity. If this mechanism is independent of both PKA activity and S156 phosphorylation, which of the following will most likely be observed?
(A) HEK cells exposed to the most hypertonic conditions will display the greatest degree of AQP5 membrane localization, allowing water to flow into the cells.
(B) HEK cells exposed to the most hypotonic conditions will display the greatest degree of AQP5 membrane localization, allowing water to flow into the cells.
(C) HEK cells exposed to the most isotonic conditions will display the greatest degree of AQP5 membrane localization, allowing water to flow into the cells.

Answer 1

Answer:

(B) HEK cells exposed to the most hypotonic conditions will display the greatest degree of AQP5 membrane localization, allowing water to flow into the cells.

Explanation:

The function of AQP5 (an aquaporin) is to allow the water to move into or out of the cell down the concentration gradient. When placed in hypotonic solutions, the internal environment of HEK cells will be hypertonic. Water always moves from hypotonic (higher water concentration) to hypertonic (lower water concentration) solution.  

Hence, the HEK cells exposed to the hypotonic conditions will localize AQP5 in their membranes to allow the water to move from out hypotonic conditions to the inner hypertonic environment.