Lithium attenuates the active transport of calcium in the larva of Aëdes aegypti.

Larvae of the freshwater mosquito Aides aegypti (L.) are able to maintain their principal electrolytes against a steep concentration gradient between the haemolymph and the external medium. The concentration of monovalent ions such as Na, K and Cl~ is kept far above that in the external medium by processes of active transport which are located in the anal papillae, the rectum and the Malpighian tubules (Koch, 1938; Ramsay, 1953; Treherne, 1954; Stobbart, 1959, 1960, 1965, 1967). Ithasbeen demonstrated that over 90 % of the exchange of monovalent ions occurs through the anal papillae (Treherne, 1954), but these organs are not permeable to bivalent ions (Wigglesworth, 1933). The processes which regulate the exchange of bivalent ions between the larva and the external medium have not yet been elucidated. Recently, we have demonstrated that larvae of Aedes aegypti maintain a saturable transport system for the uptake of calcium ions from dilute calcium solutions (Barkai & Williams, 1983). This system obeyed Michaelis-Menten kinetics and its activity was susceptible to ruthenium-red which selectively inhibits Ca-activated ATPase (Watson, Vincenzi & Davis, 1971). We now present evidence that lithium ions (Li) act in a similar manner to that of ruthenium-red in attenuating the accumulation of Ca from dilute solutions. The net Ca uptake and the Ca fluxes were estimated with Ca in early fourth instar larvae. The net Ca uptake (nmolh" larva") was determined at Ca concentrations ranging between 0-01 and 50 mM in the presence and absence of 2mM-LiCl or 2mMNaCl. Calcium fluxes were determined at a concentration of 0-1 mM-CaCl2 from the curve representing the accumulation of Ca in the larva with time (Barkai & Williams, 1983). When values for the quantity of Ca in the larva (*QL) were divided by the concentration of Ca in the medium (*QM) and plotted against time, the resulting data could be fitted quite closely to the following exponential function of time: