Effects of sodium-transport inhibitors on diuresis and mid-gut (Na+ + K+)-ATPase in the tsetse fly Glossina morsitans

The effects of four inhibitors of specific sodium-transport mechanisms on diuresis in the tsetse fly Glossina morsitans, have been determined. Ouabain (1.0, 0.1 mM) and ethacrynic acid (1.0, 0.2 mM) reduced the rate of water loss, whereas amiloride (1.0 mM) and furosemide (1.0 mM) did not. The effects of ouabain, ethacrynic acid and meal size upon the anterior mid-gut (Na⁺ + K⁺)-ATPase activity were also determined. For ouabain, the negative logarithm causing 50% inhibition of (Na⁺ + K⁺)-ATPase (pI₅₀) was 6.0, whilst ethacrynic acid together with meal size did not affect the activity of this enzyme. These results show that diuresis in this insect involves the active transport of sodium ions by both electrogenic and $\text{Na}{}^{\mathrm{+}}\text{K}{}^{\mathrm{+}}$ exchange pumps.