The excretion of NaCl and KCl loads in mosquitoes. 1. Control data

Abstract

The handling of Na+ and K+ loads was investigated in isolated Malpighian tubules and in whole mosquitoes of Aedes aegypti. Isolated Malpighian tubules bathed in Na+-rich Ringer solution secreted Na+-rich fluid, and tubules bathed in K+-rich Ringer solution secreted K+-rich fluid. Upon Na+ loading the hemolymph, the mosquito removed 77% the injected Na+ within the next 30 min. The rapid onset and magnitude of this diuresis and the excretion of more Na+ than can be accounted for by tubular secretion in vitro is consistent with the release of the calcitonin-like diuretic hormone in the mosquito to remove the Na+ load from the hemolymph. Downstream, K+ was reabsorbed with water in the hindgut, which concentrated Na+ in excreted urine hyperosmotic to the hemolymph. Upon K+ loading the hemolymph, the mosquito took 2 h to remove 100% of the injected K+ from the hemolymph. The excretion of K+-rich isosmotic urine was limited to clearing the injected K+ from the hemolymph with a minimum of Cl− and water. As a result, 43.3% of the injected Cl− and 48.1% of the injected water were conserved. The cation retained in the hemolymph with Cl− was probably N-methyl-d-glucamine, which replaced Na+ in the hemolymph injection of the K+ load. Since the tubular secretion of K+ accounts for the removal of the K+ load from the hemolymph, the reabsorption of K+, Na+, Cl−, and water must be inhibited in the hindgut. The agents mediating this inhibition are unknown.