POTASSIUM UPTAKE INTO DROSOPHILA OVARIAN FOLLICLES - RELEVANCE TO PHYSIOLOGICAL AND DEVELOPMENTAL PROCESSES

The origin of bioelectric phenomena in insect ovarian follicles is scarcely known and the presumption that these phenomena play an important role during development is still controversial. In the present study the K+ uptake mechanisms of vitellogenic Drosophila follicles were investigated in vitro using rubidium-86 as a probe. Follicles were exposed to the inhibitors 2,4-dinitrophenol, sodium azide, ouabain, 4-aminopyridine, tetraethylammonium chloride and barium chloride. The total K+ uptake changed stage-specifically and was different in anterior and posterior follicle halves. Maximal values were reached during mid-vitellogenesis (stage 10B), and at this stage K+ uptake into the posterior half (occupied by the oocyte with its columnar follicle cell epithelium) exceeded that into the anterior half (nurse cells with flat follicle cells) by 20%. This difference was probably due to ouabain-insensitive K+-pump(s) whereas the (Na+, K+)-pump was equally active in anterior and posterior halves and did not show stage-specific variations. The active K+ uptake into the anterior half increased during nurse-cell regression (stages 11 and 12). Active as well as passive K+ uptake increased with increasing extracellular pH. The used K+-channel blockers blocked K+ efflux but affected the passive K+ uptake only slightly. A juvenile hormone analogue and 20-hydroxyecdysone diminished the active K+ uptake, affecting the (Na+, K+)-pump and the other K+-pump(s) differently. In the presence of ouabain or at alkaline pH, mid-vitellogenic follicles developed in vitro rather normally up to the end of oogenesis whereas the other inhibitors as well as acidic pH blocked the course of development. The relevance of these findings for intracellular pH-regulation, osmoregulation, growth, membrane potentials, ionic currents, intrafollicular transport and other developmental processes is discussed.