Final answer:
Aquaporins are specialized transport proteins in the kidney that allow for rapid fluid movement into or out of cells. They are channel proteins that enable water to pass through the membrane at a high rate, helping to maintain water balance.
Step-by-step explanation:
The specialized transport proteins that allow for very rapid fluid movement into or out of cells in the kidney are known as aquaporins.
Aquaporins are channel proteins that provide a hydrated opening through the membrane, allowing water to pass through at a high rate.
They are critical for maintaining water balance and are found in many cells of the body, including six types specifically in the kidney.