. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 2. Model for the i. urrent patterns of a vitellogenic poly- trophic insect follicle. Bo; i n i ent loops; top: additional cur- rents allowed for by the model. ( >cvte, N: nurse cells, F: cylindrical follicle cells, f: squamous Colin i follicle cells are represented, separated from the oocyte and the nurse cells, for clarity. would have to generate an average membrane current in the furrow of the order of magnitude of 100 juA/cm2 to 1 mA/cm: to retain the bridge current. This is a high value for the activity of ion
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 2. Model for the i. urrent patterns of a vitellogenic poly- trophic insect follicle. Bo; i n i ent loops; top: additional cur- rents allowed for by the model. ( >cvte, N: nurse cells, F: cylindrical follicle cells, f: squamous Colin i follicle cells are represented, separated from the oocyte and the nurse cells, for clarity. would have to generate an average membrane current in the furrow of the order of magnitude of 100 juA/cm2 to 1 mA/cm: to retain the bridge current. This is a high value for the activity of ion pumps. If the model of Jaffe and Woodruff (1979) were to apply to other polytrophic follicles from other species, a potential gradient between oocyte and nurse cells should necessarily occur in all spe- cies and stages. One would also expect to find a concomi- tant variability for the measurements of the membrane potential as for the measurements of the extracellular electrical field. Since this is not the case, the model of JafTe and Woodruff (1979) does not completely explain all the data observed. The extrafollicular field originates on the surface of the follicle. Therefore, the follicle cells must have a modulat- ing, if not generating, contribution to this field. Woodruff et al. (1986) measured the extracellular currents of vitel- logenic follicles of Hyalophora cecropia with patches of the epithelium overlying the trophic cap removed. Un- der these conditions, the current over the trophic cap is reversed: it is now directed outward. From microinjec- tion experiments of lucifer yellow in the subepithelial spaces, the same authors conclude that the follicular epi- thelium over the trophic cap presents a barrier to ion movement. Another line of evidence that should be taken into ac- count are the dye-coupling experiments. Woodruff (1979) has shown fluorescein and electrical coupling be- tween oocytes in adjacent follicles of Hyalophora ce- cropia. Bohrmann and Gutzeit (1987
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
