Dietary calcium (Ca2+) impacts Ca2+ content and molecular expression of Ca2+-transporters in Malpighian tubules of the yellow fever mosquito, Aedes aegypti

Abstract

The renal (Malpighian) tubules of insects play important roles in hemolymph Ca²⁺ regulation. Here we investigated how dietary Ca²⁺ loads from sucrose or blood meals affect the Ca²⁺ content and mRNA expression of Ca²⁺ transporters in Malpighian tubules of adult female mosquitoes. Using the yellow fever mosquito Aedes aegypti we found that feeding females 10% sucrose with elevated Ca²⁺ concentration ad libitum for 6 days led to increased Ca²⁺ content in Malpighian tubules. The increases of Ca²⁺ content correlated with up-regulations of mRNAs encoding intracellular Ca²⁺-ATPases (SERCA and SPCA), a plasma membrane Ca²⁺-ATPase (PMCA), and a K⁺-dependent Na⁺/Ca²⁺ exchanger (NCKX1). We also found that when adult females were fed blood, tubule Ca²⁺ content changed dynamically over the next 72 h in a manner consistent with redistribution of tubule Ca²⁺ stores to other tissues (e.g., ovaries). The changes in tubule Ca²⁺ were correlated with dynamic changes in mRNA abundances of SERCA, SPCA, PMCA, and NCKX1. Our results are the first to demonstrate that Malpighian tubules of adult female mosquitoes have a remarkable capacity to handle high dietary Ca²⁺ loads, most likely through the combination of storing excess Ca²⁺ within intracellular compartments and secreting it into the tubule lumen for excretion. Our results also suggest that the Malpighian tubules play key roles in supplying Ca²⁺ to other tissues during the processing of blood meals.