Calcium transport across the basolateral membrane of isolated Malpighian tubules: a survey of several insect orders
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AbstractThe Malpighian tubules play a major role in haemolymph calcium homeostasis in insects by sequestering excess Ca2+within the biomineralized granules that often accumulate in the tubule cells and/or lumen. Using the scanning ion‐selective microelectrode technique, measurements of basolateral Ca2+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) andPogonomyrmex occidentalis(Hymenoptera). Ca2+transport is specific to tubule segments containing Ca‐rich granules inD. melanogasterandA. aegypti, whereas Ca2+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 Ca2+transport, suggesting that previous effects observed across midtubules ofA. domesticusare unique to this species. In addition, the present study is the first to provide measurements of basolateral Ca2+across single principal and secondary tubule cells, where Ca2+uptake occurs only across principal cells. Estimated times for all tubules to eliminate the entire haemolymph Ca2+content in each insect range from 6 min (D. melanogaster) to 19 h (H. halys) or more, indicating that rates of Ca2+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 Ca2+, often within specific tubule segments.
