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First published online May 15, 2009
Journal of Experimental Biology 212, 1611-1619 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.030007
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Vacuolar-type proton pumps in insect epithelia

Helmut Wieczorek1,*, Klaus W. Beyenbach2, Markus Huss1 and Olga Vitavska1

1 Department of Biology/Chemistry, University of Osnabrück, 49069 Osnabrück, Germany
2 Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA


Figure 1
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  		Fig. 1. Cryosection of the tobacco hornworm midgut epithelium. (A) Immunolocalization of the V1 subunit A by a monoclonal antibody. (B) Same section as in A, but visualized by Hoffman modulation contrast microscopy. a, apical side; b, basal side; BB, brush border the columnar cells; GC goblet cavity of goblet cells. The V-ATPase is present only in the apical membrane of goblet cells.

 

Figure 2
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  		Fig. 2. Model of a eukaryotic V-ATPase. (A) The peripheral V1 complex consists of eight different subunits identified with capital letters A–H. The integral membrane VO complex consists of at least four different subunits identified with lowercase letters (a, c, d, e). In yeast subunit c occurs together with its isoforms c' and c''. Actin filaments bind to subunits B (Holliday et al., 2000Go) and C (Vitavska et al., 2003Go). (B) Disassembly of the V-ATPase into its V1 and VO complexes. Subunit C, which dissociates from the V1 complex, binds not only to F actin but also to monomeric G-actin (Vitavska et al., 2005Go).

 

Figure 3
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  		Fig. 3. Phosphorylation of the V1 subunit C by protein kinase A (PKA) and its assumed involvement in the process of reversible V1VO disassembly.

 

Figure 4
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  		Fig. 4. The V-ATPase in Malpighian tubules of the mosquito Aedes aegypti. (A) Cross-section of the abdomen. Immunofluorescence labeling of subunit C of the V-type H+-ATPase at the luminal brush border of Malpighian tubules (courtesy of H. Merzendorfer). (B) Sections of Malpighian tubules. Immunoperoxidase labeling of the B-subunit of the V-type H+-ATPase at the brush border of principal cells. The V-ATPase is not present in stellate cells (adapted from Weng et al., 2003Go). Scale bars in A and B are 100 µm.

 

Figure 5
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  		Fig. 5. Molecular and electrical models for powering the transepithelial secretion of NaCl, KCl and water in Malpighian tubules of Ae. aegypti under control conditions. Principal cells mediate the transepithelial active transport of Na+ and K+ driven by the V-type H+ ATPase collaborating with a putative electrogenic H+/cation exchanger (NHA?) located at the apical membrane. Stellate cells and the septate junction mediate the passive transepithelial secretion of Cl–. Active and passive transepithelial transport routes are electrically coupled via septate and gap junctions. Red arrows indicate the flow of positive charge, where current can be carried by negative charge (anion) flowing in the opposite direction. R, resistance; a and a(s) apical membrane of principal and stellate cell, respectively; bl and bl(s), basolateral membrane of principal and stellate cell, respectively; gap, gap junction; para, paracellular pathway; AE, electroneutral anion exchanger; NHE3, electroneutral Na+/H+ exchanger type 3. The paracellular pathway between principal and stellate cells is not depicted. Data from previous publications (Beyenbach, 2001Go; Beyenbach and Masia, 2002Go; O'Connor and Beyenbach, 2001Go; Piermarini et al., 2008).

 

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