Sodium and chloride regulation in freshwater and osmoconforming larvae of Culex mosquitoes.
Some evidence concerning the influence of various ions upon the fluxes and net uptake of sodium by the aquatic larva of Aides aegypti was described in an earlier paper (Stobbart, 1965). One of the main findings was that chloride in the external medium has, in concentrations up to 5 mM/1., a marked stimulatory effect upon sodium influx and net uptake. While the sodium pump (which occurs mainly in the anal papillae) is known in some detail (Ramsay, 1953; Treherne, 1954; Stobbart, 1959, i960, 1965) no information is available about chloride fluxes in this species. However, a sodiumindependent net chloride uptake has been demonstrated, and measurements of potential difference between haemolymph and medium show that the haemolymph chloride concentration must be maintained actively against an adverse electrochemical gradient (Stobbart, 1965). Furthermore, Koch (1938) showed that net chloride uptake by chloride-depleted larvae of the closely related Culex, and of Chironomus, occurs only if the anal papillae are intact. The evidence therefore suggests that culicine larvae possess well-developed mechanisms in the anal papillae for the uptake of chloride, and it is my purpose in this paper to describe work aimed at elucidating aspects of the mechanism for chloride uptake in Aides aegypti larvae, and to consider in more detail than was achieved earlier (Stobbart, 1965) the question of interaction of sodium and chloride during their passage through the anal papillae. Following earlier practice I shall use the terms 'influx* and 'outflux' to describe ionic fluxes found with radioactive tracers, and the terms 'net loss', 'loss', 'net uptake' and 'uptake' to describe net movements of ions.