Electrical Potential Differences and Ionic Transport in the Larva of the Mosquito Aedes Aegypti (L.)

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Abstract
1. Measurements have been made, in the 4th-instar freshwater larva of the mosquito Aëdes atgypti, of (i) potential differences between haemolymph and medium; (ii) the effects upon sodium fluxes of metabolic inhibitors and of sodium-free solutions. 2. The measurements of potential differences together with those of the Na, Cl, and K concentrations in the larvae show that Na and Cl are actively transported from the medium into the haemolymph, whereas K is probably taken up passively in company with Cl. 3. Using Goldman's constant-field equation and the present, and earlier, data it can be shown that the expected passive fluxes of Na and Cl between the larvae and the medium are very much smaller than the observed fluxes. 4. KCN and de-ionized water immediately reduced Na outflux to one-sixth to one-seventh of the normal value; KCN also inhibits Na influx more or less completely. 5. The passive Na fluxes through the anal papillae (which cause almost all the ionic movements) appear to be very small. 6. Overall the data show that the influxes and outfluxes of Na and Cl cannot be explained in terms of passive movements. Nor can the increased outflux of these ions which is observed at high external concentrations be explained by Kirschner's theory of ‘back-transport’. The data, however, are fully compatible with a model for ionic pumps suggested earlier, which would cause both net uptake and exchange of an ion. The data are discussed in terms of a refined version of this model.

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