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The vacuolar-type proton pump (V-ATPase) uses the energy of ATP hydrolysis for the electrogenic transport of protons across membranes. V-ATPase is organized in two sectors, a membrane-integral VO domain that conducts protons across the membrane, and a cytosolic V1 domain that contains the ATPase activity. Various mechanisms have been implicated with the regulation of V-ATPase activity, e.g. reversible disassembly of functional V1VO holoenzymes into inactive VO and V1 domains.
We use the salivary gland of the blowfly (Calliphora vicina) as a model system to determine how assembly/disassembly of V-ATPase is regulated. In this organ, the neurohormone serotonin (5-HT) elicits production of a KCl-rich saliva, and this process is energized by V-ATPase-dependent H+-transport and hyperpolarization of the apical membrane. 5-HT-induced activation of V-ATPase goes along with an assembly of V-ATPase holoenzymes on the apical membrane of the secretory cells. Using optophysiological, electrophysiological, fluorescence microscopic and molecular biological techniques, we have disclosed the signaling sequence between 5-HT receptors on the basolateral membrane and V-ATPase assembly on the apical membrane (see scheme below).