Dube K A, McDonald D G, O'Donnell M J
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
Arch Insect Biochem Physiol. 2000 May;44(1):27-39. doi: 10.1002/(SICI)1520-6327(200005)44:1<27::AID-ARCH4>3.0.CO;2-I.
Calcium homeostasis in Drosophila melanogaster was examined in response to the challenges imposed by growth, reproduction and variations in dietary calcium content. Turnover time for calcium, calculated as the time for (45)Ca(2+)to accumulate to half the steady state value of 3.46 nmol/fly, was 3.3 days. Although larvae weighed 2x as much as adults, they contained 3-4x as much calcium. Anterior Malpighian tubules (Mts) contain much more calcium than posterior Mts, accounting for 25-30% of the calcium content of the whole fly. In response to a 6.2-fold increase in dietary calcium level, calcium content of whole flies increased only 10%. Hemolymph calcium concentration ( approximately 0.5 mM) was similar in males and females and in animals raised on diets differing in calcium content. Fluid secretion rate, secreted fluid calcium concentration, and transepithelial calcium flux in tubules isolated from flies raised on high and low calcium diets did not differ significantly. Malpighian tubules secrete calcium at rates sufficient to eliminate whole body calcium content in 0.5 and 3 days for tubules secreting fluid at basal and maximal rates, respectively. It is suggested that flies absorb high quantities of calcium from the diet and maintain homeostasis through the combined effects of elimination of calcium in fluid secreted by the Malpighian tubules and the sequestration of calcium in granules, especially within the distal segment of the anterior pair of Malpighian tubules.
为应对生长、繁殖以及饮食钙含量变化所带来的挑战，对黑腹果蝇的钙稳态进行了研究。钙的周转时间，即（45）Ca（2+）积累至3.46 nmol/果蝇的稳态值一半所需的时间，为3.3天。尽管幼虫的体重是成虫的2倍，但它们所含的钙却是成虫的3至4倍。前马氏管比后马氏管含有更多的钙，占整个果蝇钙含量的25%至30%。饮食钙水平增加6.2倍时，整个果蝇的钙含量仅增加了10%。雌雄果蝇以及以钙含量不同的饮食饲养的动物，其血淋巴钙浓度（约0.5 mM）相似。从高钙和低钙饮食饲养的果蝇中分离出的小管，其液体分泌速率、分泌液钙浓度和跨上皮钙通量没有显著差异。马氏管分别以基础速率和最大速率分泌液体时，分泌钙的速率足以在0.5天和3天内消除全身的钙含量。研究表明，果蝇从饮食中吸收大量的钙，并通过马氏管分泌液中钙的消除以及钙在颗粒中的螯合作用（尤其是在前一对马氏管的远端段内）的综合效应来维持钙稳态。
