Location of the a3-containing V-ATPases in resorbing osteoclasts. Osteoclasts require expression of functional a3-subunit even though they also express a1 and a2. The top panels show confocal images of a resorbing osteoclast on a bone slice stained with phalloidin-to detect microfilaments and with an anti-E-subunit antibody to detect V-ATPases. Notice that the microfilaments are concentrated in a structure called the actin ring. The actin ring surrounds the V-ATPases in the ruffled plasma membrane where most V-ATPases are concentrated. Below is a schematic showing a side view of a resorbing osteoclasts with actin filaments green and V-ATPases red. The resorption compartment is the site of bone degradation.