Transport of H+, Na+ and K+ across the posterior midgut of blood-fed mosquitoes (Aedes aegypti)

Following ingestion of a blood meal, the adult female mosquito undergoes a massive diuresis during which Na+, Cl− and water are secreted at high rates by the Malpighian tubules. In the hours following completion of diuresis, digestion of the K+-rich blood cells provides a source of energy as well as amino acids for proteins in the developing eggs. Although the transport of inorganic ions by the Malpighian tubules of blood-fed mosquitoes has been extensively characterized, relatively little is known of the epithelial transport mechanisms responsible for movement of Na+, H+, and K+ across the posterior midgut. In this paper we have used the Scanning Ion-selective Electrode Technique (SIET) to measure the basal (unstimulated) rates of transport of K+, Na+ and H+ across the isolated posterior midgut at intervals after the blood meal. We have also measured luminal concentrations of Na+ and K+ and the transepithelial electrical potential at the same time points and have calculated the electrochemical potentials for Na+, K+ and H+ across the midgut. SIET measurements reveal absorption (lumen to bath) of Na+ and H+ and secretion of K+ for the first 2 h after blood-feeding. By 24 h after the meal, absorption of Na+ and H+ remains active while there is an electrochemical gradient favouring absorption of K+. Inhibition by ouabain and Ba2+ suggest a role for the Na+/K+-ATPase and K+ channels in absorption of Na+ and K+, respectively. Inhibition of H+ absorption by acetazolamide implicates carbonic anhydrase in transepithelial H+ transport.