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

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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.