Question

Here is a chloride cell in the gill epithelium of a fish. For reference, NKA = Na+/K+ ATPase NKCC = Na+/K+/Cl- cotransporter. CFTR MRC -mV+mv NKCC NKA 3Na Na K 2C1 Reference: chloride cell Given that the chloride cells of salt water fish have the NKCC transporter on the basal (bottom) side of the epithelium, what do you predict regarding the NKCC transporter in chloride cells of freshwater fish? O A. The transporter must move chloride in the opposite direction, but from the apical (top) side of the cell. OB. The NKCC transporter, as localized in salt water fish, could also work in freshwater fish. OC. The transporter must move chloride in the opposite direction, also from the bottom side of the cell. OD. A transporter is not needed to move CI-ions into cells from fresh water.

Answer 1

Option A is correct - The transporter must move chloride in the opposite direction, but from the apical (top) side of the cell.

Apical location indicates the localization of the cell towards the environment and basolateral localization indicates an internal location of the cell (towards the body).

Marine fishes maintain osmotic gradient of chlorine by drinking saline water and absorbing the chloride ions internally through the NKCC transporters present on the basolateral side of the chloride cells.

In case of freshwater fishes, they absorb chloride ions from the environment through the gills to maintain an osmotic balance. Thus chlorine needs to be absorbed from the environment into the body through the gills.It is evident that this is the opposite of the strategy adopted by the salt water fishes.

Thus the localization of the NKCC transporter should be on the apical side (towards the environment) for the movement of chloride in the opposite direction (opposite to the direction of saltwater fishes).