Distribution of Na+,K(+)-ATPase in photoreceptor cells of insects

Dietary restriction and the transcription factor clock delay eye aging to extend lifespan in Drosophila Melanogaster

Many vital processes in the eye are under circadian regulation, and circadian dysfunction has emerged as a potential driver of eye aging. Dietary restriction is one of the most robust lifespan-extending therapies and amplifies circadian rhythms with age. Herein, we demonstrate that dietary restriction extends lifespan in Drosophila melanogaster by promoting circadian homeostatic processes that protect the visual system from age- and light-associated damage. Altering the positive limb core molecular clock transcription factor, CLOCK, or CLOCK-output genes, accelerates visual senescence, induces a systemic immune response, and shortens lifespan. Flies subjected to dietary restriction are protected from the lifespan-shortening effects of photoreceptor activation. Inversely, photoreceptor inactivation, achieved via mutating rhodopsin or housing flies in constant darkness, primarily extends the lifespan of flies reared on a high-nutrient diet. Our findings establish the eye as a diet-sensitive modulator of lifespan and indicates that vision is an antagonistically pleiotropic process that contributes to organismal aging.

Distribution and serotonin-induced activation of vacuolar-type H+-ATPase in the salivary glands of the blowfly Calliphora vicina

Secretory activity in blowfly salivary glands is activated by the hormone serotonin. We have investigated the distribution and activity of two cation pumps that are possibly involved with transepithelial ion transport, i.e. Na(+)/K(+)-ATPase and vacuolar-type H(+)-ATPase (V-ATPase). By immunofluorescence labelling of secretory cells, Na(+)/K(+)-ATPase was localized on the basolateral plasma membrane and V-ATPase on the highly folded apical membrane. Activities of both ATPases were probed in salivary gland homogenates by applying specific inhibitors for these ion pumps, namely ouabain and bafilomycin A(1). In control glands, bafilomycin-A(1)-sensitive V-ATPase activity and ouabain-sensitive Na(+)/K(+)-ATPase activity accounted for 36% and 19%, respectively, of the total ATPase activity. V-ATPase activity increased approximately twofold after stimulation with serotonin, whereas Na(+)/K(+)-ATPase activity was not significantly affected. Biochemical assays provided evidence that the serotonin-induced activation of V-ATPase activity was accompanied by a recruitment of peripheral V(1) subunits from the cytosol to the plasma membrane, indicative of the assembly of V(0)V(1) holoenzymes. These data show that a V-ATPase located in the apical plasma membranes of the secretory cells is a component of the apical "potassium pump" that has been identified previously by physiological approaches. The V-ATPase energizes the apical membrane and provides the primary driving force for fuelling a putative K(+)/nH(+) antiporter and, thus, for fluid secretion. Serotonin-induced assembly of V(0)V(1) holoenzymes might constitute a regulatory mechanism for the control of pump activity.