Ion physiology of vitellogenic follicles |
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Authors: | Telfer William H Woodruff Richard I |
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Institution: | a Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA b Department of Biology, West Chester University, West Chester, PA 19383-2130, USA |
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Abstract: | The ion physiology of vitellogenic follicles from a lepidopteran (Hyalophora cecropia) and a hemipteran (Rhodnius prolixus) are compared. Similarities that can be expected to occur in vitellogenic follicles of many other insects include: (1) gap junctions, which unite the cells of a follicle into an integrated electrical system, (2) transmembrane K+ and H+ gradients that account for over 60% of follicular membrane potentials, (3) absence of a Cl− potential, (but the opening of channels to this anion when vitellogenesis terminates in H. cecropia), (4) an electrogenic proton pump that supplements follicular membrane potentials, (5) Ca2+ action potentials evoked by injecting depolarizing currents into oocytes, and (6) the use of osmotic pressure to control epithelial patency. Differences include: a Na+/K+-ATPase that accounts for about 20% of the follicular resting potential in R. prolixus but is absent from H. cecropia, and an intrafollicular Ca2+ current that moves from oocyte to nurse cells through cytoplasmic bridges in H. cecropia. Evidence is also summarized for two promising mechanisms that require further substantiation: (1) transmission via gap junctions of a follicle cell product that promotes endocytosis in the oocyte; and (2) transport of the proton pump back and forth between cell surface and endosomes as the membrane that carries it recycles through successive rounds of vitellogenin uptake. |
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Keywords: | Gap junction Ion gradients Osmotic pressure Proton pump Resting potential |
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