Which of the following is true regarding aquaporins and water permeability of the collecting duct?
A. Aquaporin-2 and aquaporin-3 proteins are inserted into the apical membrane of principal cells of the collecting duct when ADH binds to receptors on these cells.
B. Aquaporin-3 proteins are present in the basolateral membrane of principal cells of the collecting duct at all times.
C. Aquaporin-2 proteins are present in the apical membrane of the principal cells of the collecting duct at all times.
D. Some water is able to diffuse across the principal cells of the collecting duct without the use of aquaporins.
