The plus end projects away from the organizing centers. One group of motors move vesicles toward the organizing centers at the minus end, and another group move vesicles away from the organizing centers toward the plus end. In collecting duct cells, many organizing centers are near the apex of the cell, and microtubules project from them down toward the base and sides of the cell. In these cells, a motor which moves along the microtubule toward the minus end in the apex of the cell would be expected to be the motor which moves the vesicle-encased AQP2 to the membrane at the apex of the cell. One candidate motor is dynein , a large protein with the collecting duct cell.
Research suggests that dynein needs help to move vesicles along the microtubule.
Specifically, it needs the protein complex dynactin , which may help dynein link with vesicles. Marples, et al, sought to confirm whether or not dynein and dynactin were associated with AQP2-bearing vesicles. To do so, they examined rat kidney tissue, first to see if dynein and dynactin were present and then to see if they were associated with AQP2. The authors used analytical techniques such as immunoblotting , immunoisolation , immunocytochemistry and immunoelectron microscopy , all of which identify proteins by means of antigen-antibody specific reactions. Their analyses was able to demonstrate that cellular dynein was present in the rat kidney, being most abundant in the kidney's inner medulla , next most abundant in the outer medulla and least abundant in the kidney cortex .