In Bsg(-/-) mice, there is a severe reduction in accumulation of the MCT1 and -3 proteins in the RPE and a concomitant reduction in MCT1 and -4 in the neural retina supporting a role for 5A11/basigin in the targeting of these transporters to the plasma membrane. Decreased expression of MCT1 and -4 on the surfaces of Müller and photoreceptor cells may compromise energy metabolism in the outer retina, leading to abnormal photoreceptor cell function and degeneration.

The cellular localization of glutamine synthetase [

The midgut of mosquito larvae maintains a specific lumen alkalinization profile with large longitudinal gradients (pH Ϸ 3 units⅐mm ؊1 ) in which an extremely alkaline (pH Ϸ 11) anterior midgut lies between near-neutral posterior midgut and gastric cecum (pH 7-8). A plasma membrane H ؉ V-ATPase energizes this alkalinization but the ion carriers involved are unknown. Capillary zone electrophoresis of body samples with outlet conductivity detection showed a specific transepithelial distribution of chloride and bicarbonate͞carbonate ions, with high concentrations of both anions in the midgut tissue: 68.3 ؎ 5.64 and 50.8 ؎ 4.21 mM, respectively. Chloride was higher in the hemolymph, 57.6 ؎ 7.84, than in the lumen, 3.51 ؎ 2.58, whereas bicarbonate was higher in the lumen, 58.1 ؎ 7.34, than the hemolymph, 3.96 ؎ 2.89. Timelapse video assays of pH profiles in vivo revealed that ingestion of the carbonic anhydrase inhibitor acetazolamide and the ion exchange inhibitor DIDS (4,4-diisothiocyanatostilbene-2,2-disulfonic acid), at 10 ؊4 M eliminates lumen alkalinization. Basal application of these inhibitors in situ also reduced gradients recorded with self-referencing pH-sensitive microelectrodes near the basal membrane by Ϸ65% and 85% respectively. Self-referencing chlorideselective microelectrodes revealed a specific spatial profile of transepithelial chloride transport with an efflux maximum in anterior midgut. Both acetazolamide and DIDS reduced chloride effluxes. These data suggest that an H ؉ V-ATPase-energized anion exchange occurs across the apical membrane of the epithelial cells and implicate an electrophoretic Cl ؊ ͞HCO 3 ؊ exchanger and carbonic anhydrase as crucial components of the steady-state alkalinization in anterior midgut of mosquito larvae.T he human stomach works at an acid pH near 1, whereas the larval mosquito midgut works at an alkaline pH near 11. The acid pH of mammalian stomachs has been thoroughly investigated and its mechanisms are understood in great detail. The alkaline pH of larval mosquito midguts has been little studied and remains largely a mystery. Recently developed techniques for direct analysis of the intact midgut in vivo and in semi-intact larvae, with a resolution that allows analytical assay of small patches of tissue, even of individual cells, have led to insights into the alkalinization mechanism.The principal function of the larval mosquito midgut is to digest and absorb nutrients. High pH values have been recorded in anterior midgut of several mosquito larvae, including Aedes aegypti (1), as well as in some lepidopteran larvae with high tannin diet (2). The alkaline environment of the anterior midgut lumen enhances dissociation of tannin-protein complexes and, therefore, would be advantageous for the nutrition of herbivorous and detritus-feeding larvae (3). The tannin-free protein could then be digested and absorbed at the near neutral pH of posterior midgut lumen (3, 4). This pattern of nutrient processing has led to the large longitudinal gradients of pH and ionic concentrat...