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Journal Article

Alkalinization by Chloride/Bicarbonate Pathway in Larval Mosquito Midgut

Dmitri Y. Boudko, Leonid L. Moroz, William R. Harvey and Paul J. Linser
Proceedings of the National Academy of Sciences of the United States of America
Vol. 98, No. 26 (Dec. 18, 2001), pp. 15354-15359
Stable URL: http://www.jstor.org/stable/3057460
Page Count: 6

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Topics: Midgut, pH, Anions, Larvae, Chlorides, Mosquitos, Lumens, Insect larvae, Ions, Bicarbonates
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Alkalinization by Chloride/Bicarbonate Pathway in Larval Mosquito Midgut
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Abstract

The midgut of mosquito larvae maintains a specific lumen alkalinization profile with large longitudinal gradients (pH ≈ 3 units·mm-1) in which an extremely alkaline (pH ≈ 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 bicarbonate/carbonate 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 ≈65% 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-/HCO3 - exchanger and carbonic anhydrase as crucial components of the steady-state alkalinization in anterior midgut of mosquito larvae.

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