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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Hormone-induced assembly and activation of V-ATPase in blowfly salivary glands is mediated by protein kinase A

Institut für Biochemie und Biologie, Universität Potsdam, Potsdam, Germany

Submitted 30 January 2007 ; accepted in final form 10 October 2007

The vacuolar H⁺-ATPase (V-ATPase) in the apical membrane of blowfly (Calliphora vicina) salivary gland cells energizes the secretion of a KCl-rich saliva in response to the neurohormone serotonin (5-HT). We have shown previously that exposure to 5-HT induces a cAMP-mediated reversible assembly of V₀ and V₁ subcomplexes to V-ATPase holoenzymes and increases V-ATPase-driven proton transport. Here, we analyze whether the effect of cAMP on V-ATPase is mediated by protein kinase A (PKA) or exchange protein directly activated by cAMP (Epac), the cAMP target proteins that are present within the salivary glands. Immunofluorescence microscopy shows that PKA activators, but not Epac activators, induce the translocation of V₁ components from the cytoplasm to the apical membrane, indicative of an assembly of V-ATPase holoenzymes. Measurements of transepithelial voltage changes and microfluorometric pH measurements at the luminal surface of cells in isolated glands demonstrate further that PKA-activating cAMP analogs increase cation transport to the gland lumen and induce a V-ATPase-dependent luminal acidification, whereas activators of Epac do not. Inhibitors of PKA block the 5-HT-induced V₁ translocation to the apical membrane and the increase in proton transport. We conclude that cAMP exerts its effects on V-ATPase via PKA.

vacuolar H⁺-adenosine 5'-triphosphatase; adenosine 3',5'-cyclic monophosphate; exchange protein directly activated by adenosine 3',5'-cyclic monophosphate; insect

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