Protein kinase A-dependent and -independent activation of the V-ATPase in Malpighian tubules of Aedes aegypti.

Transepithelial ion transport in insect Malpighian tubules is energized by an apical V-ATPase. In hematophagous insects, a blood meal during which the animal ingests huge amounts of salt and water stimulates transepithelial transport processes linked to V-ATPase activation, but how this is accomplished is still unclear. Here we report that membrane-permeant derivatives of cAMP increase the bafilomycin-sensitive ATPase activity in Malpighian tubules of Aedes aegypti twofold and activate ATP-dependent transport processes. In parallel, membrane association of the V(1) subunits C and D increases, consistent with the assembly of the holoenzyme. The protein kinase A inhibitor H-89 abolishes all cAMP-induced effects, consistent with protein kinase A (PKA) being involved in V-ATPase activation. Metabolic inhibition induced by KCN, azide and 2,4-dinitrophenol, respectively, also induces assembly of functional V-ATPases at the membrane without PKA involvement, indicating a phosphorylation-independent activation mechanism.