Fig. 7.

Potential modes of transport in the anterior midgut of the mosquito Aedes aegypti to achieve luminal alkalinization. (A) Alkalinization of the lumen is achieved via an apical Na⁺/CO₃^2– co-transporter of unknown stoichiometry. This process is initiated by 5-HT stimulation of basolateral H⁺-ATPase pumping and an unusually high pH_i. CO₃^2– is proposed to be derived from either amino acid (aa) catabolism or CO₂ hydration and subsequent H⁺ removal. (B) In this model, luminal alkalinization is achieved by the coordinated action of an apical electrogenic Na⁺/HCO₃^– co-transporter of unknown stoichiometry (n) and an apical electrogenic Na⁺/H⁺ antiporter (NHA). Upon secretion into the lumen, HCO₃^– is converted to CO₃^2– and H⁺ and the H⁺ is re-absorbed into the cell via a NHA and then pumped across the basolateral membrane by the action of a basolateral H⁺ ATPase. The other components of the model are the same as described for part A of this figure. PKC, protein kinase C; 5-HT₇r, 5-HT₇ receptor.