Influence of ouabain on Na+ and K+ concentration in haemolymph of Drosophila hydei and appearance of Malpighian tubules

After injection of ouabain into the body cavity, the Malpighian tubules of Drosophila larvae show a characteristic appearance which differs from the normal. The primary urine, which is mainly found in particles, is diluted and the concretions are washed away through the proximal part of the tubule and the ureter into the hindgut. In the haemolymph the Na⁺ and K⁺ concentrations change significantly. The K⁺ concentration increases rapidly to double the normal, while later the Na⁺ concentration rises up to 2·3 times the normal. Water movements are not the cause of the concentration changes because the quotient $\text{Na}\text{K}$ varies widely. Thus primary ion regulation mechanisms are influenced in the insect body by application of g-strophanthin. This is evidence for the existence of a ouabain-sensitive ATPase, which is decisively involved in the ion transport mechanisms in the insect body.