Effects of dietary calcium (Ca2+) and blood feeding on the immunochemical expression of the plasma membrane Ca2+-ATPase (PMCA) in Malpighian tubules of adult female mosquitoes (Aedes aegypti)

Abstract

Insect Malpighian tubules contribute to Ca2+ homeostasis via Ca2+ storage in intracellular compartments, Ca2+ secretion into the tubule lumen, and Ca2+ reabsorption into the hemolymph. A plasma membrane Ca2+-ATPase (PMCA) is hypothesized to be a Ca2+-transporter involved in renal Ca2+ transport of insects, however few studies have investigated its immunochemical expression in Malpighian tubules. Here we characterized the abundance and localization of PMCA-like immunoreactivity in Malpighian tubules of adult female mosquitoes Aedes aegypti using an antibody against Drosophila melanogaster PMCA. Western blotting revealed expression of a relatively abundant 109 kDa isoform and a relatively sparse 115 kDa isoform. Feeding mosquitoes 10% sucrose with 50 mM CaCl2 for 7 days did not affect PMCA immunoreactivity. However, at 24, 48, and 96 h post-blood feeding (PBF), the relative abundance of the 109 kDa isoform decreased while that of the 115 kDa isoform increased. Immunolabeling of Malpighian tubules revealed PMCA-like immunoreactivity in both principal and stellate cells; principal cell labeling was intracellular, whereas stellate cell labeling was along the basal membrane. Blood feeding enhanced immunolabeling of PMCA in stellate cells but weakened that in principal cells. Moreover, a unique apicolateral pattern of PMCA-like immunolabeling occurred in principal cells of the proximal segment at 24 h PBF, suggesting potential trafficking to septate junctions. Our results suggest PMCA isoforms are differentially expressed and localized in mosquito Malpighian tubules where they contribute to redistributing tubule Ca2+ during blood meal processing.