Fluid secretion by the malpighian tubules of the tsetse fly Glossina morsitans: the effects of ouabain, ethacrynic acid and amiloride.

The effects of three inhibitors of sodium transport on the secretion of fluid by the Malpighian tubules of Glossina morsitans have been observed. The cardiac glycoside, ouabain, affects neither the rate of secretion nor the sodium concentration of the fluid secreted when isolated tubules are bathed by solutions containing a range of sodium and potassium concentrations. Secretion is inhibited, however, by ethacrynic acid and amiloride. The results confirm that fluid secretion by the Malpighian tubules of this insect is dependent on the active transport of sodium ions and show that Na+/k+ exchange pumps are not involved in this process.