Ammonium secretion by Malpighian tubules of Drosophila melanogaster: application of a novel ammonium-selective microelectrode

Ammonia is a toxic nitrogenous waste product of amino acid metabolism that may accumulate to high levels in the medium ingested by larvae of the fruit fly Drosophila melanogaster. Here we report measurements of haemolymph NH4(+) concentration and the secretion of NH4(+) by the Malpighian (renal) tubules. Measurement of NH4(+) concentrations in secreted droplets is complicated either by the requirement for large sample volumes for enzymatic …