Na, K‐ATPase and V‐ATPase in ovarian follicles of Drosophila melanogaster

Uncovering the cause and meaning of bioelectric phenomena in developing systems requires investigations of the distribution and activity of ion‐transport mechanisms. In order to identify and localize ion pumps in ovarian follicles of Drosophila , we used immunofluorescence microscopy, immunoelectron microscopy, subcellular fractionation, immunoblots, and acridine‐orange staining. We applied various antibodies directed against the Na, K‐pump (Na, K‐ATPase) and against vacuolar‐type proton pumps (V‐ATPases). During all phases of oogenesis, Na, K‐ATPases were found in apical and lateral follicle‐cell membranes and, during rapid follicle growth (beginning with stage 10), also in nurse‐cell membranes and in the oolemma. V‐ATPases were detected in various cytoplasmic vesicles and in yolk spheres and, beginning with stage 10, also in apical follicle‐cell membranes and in the oolemma. Given these and earlier results, we propose that: 1) V‐ATPases coupled to secondary active antiporters represent the ouabain‐insensitive potassium pumps described previously; 2) both Na, K‐ATPases and V‐ATPases are involved in bioelectric phenomena as well as in osmoregulation and follicle growth, especially during stages 10–12; 3) organelle‐associated V‐ATPases play a role in vesicle acidification and in yolk processing; and 4) the channel‐forming protein ductin is a component of both V‐ATPases and gap junctions in ovarian follicles of Drosophila .