Background Alterations of bioelectrical properties of cells and tissues are known to function as wide-ranging signals during development, regeneration and wound-healing in several species. The Drosophila follicle-cell epithelium provides an appropriate model system for studying the potential role of electrochemical signals, like intracellular pH (pH i ) and membrane potential (V mem ), during development. Therefore, we analysed stage-specific gradients of pH i and V mem as well as their dependence on specific ion-transport mechanisms. Results Using fluorescent indicators, we found distinct alterations of pH i - and V mem -patterns during stages 8 to 12 of oogenesis. To determine the roles of relevant ion-transport mechanisms in regulating pH i and V mem and in establishing stage-specific antero-posterior and dorso-ventral gradients, we used inhibitors of Na + /H + -exchangers and Na + -channels (amiloride), V-ATPases (bafilomycin), ATP-sensitive K + -channels (glibenclamide), voltage-dependent L-type Ca 2+ -channels (verapamil), Cl − -channels (9-anthroic acid) and Na + /K + /2Cl − -cotransporters (furosemide). Either pH i or V mem or both parameters were affected by each tested inhibitor. While the inhibition of Na + /H + -exchangers (NHE) and amiloride-sensitive Na + -channels or of V-ATPases resulted in relative acidification, inhibiting the other ion-transport mechanisms led to relative alkalisation. The most prominent effects on pH i were obtained by inhibiting Na + /K + /2Cl − -cotransporters or ATP-sensitive K + -channels. V mem was most efficiently hyperpolarised by inhibiting voltage-dependent L-type Ca 2+ -channels or ATP-sensitive K + -channels, whereas the impact of the other ion-transport mechanisms was smaller. In case of very prominent effects of inhibitors on pH i and/or V mem , we also found strong influences on the antero-posterior and dorso-ventral pH i - and/or V mem -gradients. For example, inhibiting ATP-sensitive K + -channels strongly enhanced both pH i -gradien...

Background During Drosophila oogenesis, the follicular epithelium differentiates into several morphologically distinct follicle-cell populations. Characteristic bioelectrical properties make this tissue a suitable model system for studying connections between electrochemical signals and the organisation of the cytoskeleton. Recently, we have described stage-specific transcellular antero-posterior and dorso-ventral gradients of intracellular pH (pHi) and membrane potential (Vmem) depending on the asymmetrical distribution and/or activity of various ion-transport mechanisms. In the present study, we analysed the patterns of basal microfilaments (bMF) and microtubules (MT) in relation to electrochemical signals. Results The bMF- and MT-patterns in developmental stages 8 to 12 were visualised using labelled phalloidin and an antibody against acetylated α-tubulin as well as follicle-cell specific expression of GFP-actin and GFP-α-tubulin. Obviously, stage-specific changes of the pHi- and Vmem-gradients correlate with modifications of the bMF- and MT-organisation. In order to test whether cytoskeletal modifications depend directly on bioelectrical changes, we used inhibitors of ion-transport mechanisms that have previously been shown to modify pHi and Vmem as well as the respective gradients. We inhibited, in stage 10b, Na+/H+-exchangers and Na+-channels with amiloride, V-ATPases with bafilomycin, ATP-sensitive K+-channels with glibenclamide, voltage-dependent L-type Ca2+-channels with verapamil, Cl−-channels with 9-anthroic acid and Na+/K+/2Cl−-cotransporters with furosemide, respectively. The correlations between pHi, Vmem, bMF and MT observed in different follicle-cell types are in line with the correlations resulting from the inhibition experiments. While relative alkalisation and/or hyperpolarisation stabilised the parallel transversal alignment of bMF, acidification led to increasing disorder and to condensations of bMF. On the other hand, relative acidification as well as hyperpolarisation stabilised the longitudinal orientation of MT, whereas alkalisation led to loss of this arrangement and to partial disintegration of MT. Conclusions We conclude that the pHi- and Vmem-changes induced by inhibitors of ion-transport mechanisms simulate bioelectrical changes occurring naturally and leading to the cytoskeletal changes observed during differentiation of the follicle-cell epithelium. Therefore, gradual modifications of electrochemical signals can serve as physiological means to regulate cell and tissue architecture by modifying cytoskeletal patterns.

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