Calcium transport across the basolateral membrane of isolated Malpighian tubules: a survey of several insect orders

Abstract The Malpighian tubules play a major role in haemolymph calcium homeostasis in insects by sequestering excess Ca 2+ within the biomineralized granules that often accumulate in the tubule cells and/or lumen. Using the scanning ion‐selective microelectrode technique, measurements of basolateral Ca 2+ transport are determined at several sites along the length of the Malpighian tubules isolated from the eight insects representing seven orders: Drosophila melanogaster (Diptera), Aedes aegypti (Diptera), Tenebrio molitor (Coleoptera), Acheta domesticus (Orthoptera), Trichoplusia ni (Lepidoptera), Periplaneta americana (Blattodea), Halyomorpha halys (Hemiptera) and Pogonomyrmex occidentalis (Hymenoptera). Ca 2+ transport is specific to tubule segments containing Ca‐rich granules in D. melanogaster and A. aegypti , whereas Ca 2+ transport is relatively uniform along the length of whole tubules in the remaining species. Generally, manipulation of second messenger pathways using cAMP and thapsigargin has little effect on rates of basolateral Ca 2+ transport, suggesting that previous effects observed across midtubules of A. domesticus are unique to this species. In addition, the present study is the first to provide measurements of basolateral Ca 2+ across single principal and secondary tubule cells, where Ca 2+ uptake occurs only across principal cells. Estimated times for all tubules to eliminate the entire haemolymph Ca 2+ content in each insect range from 6 min ( D. melanogaster ) to 19 h ( H. halys ) or more, indicating that rates of Ca 2+ uptake by the Malpighian tubules are not always rapid. The results of the present study suggest that the principal cells of the Malpighian tubules contribute to haemolymph calcium homeostasis by sequestering excess Ca 2+ , often within specific tubule segments.