Alkalinization by chloride/bicarbonate pathway in larval mosquito midgut.
The midgut of mosquito larvae maintains a specific lumen alkalinization profile with large longitudinal gradients (pH approximately 3 units*mm(-1)) in which an extremely alkaline (pH approximately 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. Time-lapse 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 approximately 65% and 85% respectively. Self-referencing chloride-selective 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.
Boudko
D Y
DY
The Whitney Laboratory, University of Florida, St. Augustine, FL 32086, USA. boudko@whitney.ufl.edu
Moroz
L L
LL
Harvey
W R
WR
Linser
P J
PJ
D000468:Alkalies / Q000737:chemistry*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D009033:Culicidae / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D019075:Electrophoresis, Capillary; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007814:Larva / Q000378:metabolism*; D008839:Microelectrodes
D000468:Alkalies; D001639:Bicarbonates; D002712:Chlorides