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Figure 2


Fig. 2. Transepithelial secretion of NaCl and KCl by Malpighian tubules of the yellow fever mosquito. (A) Minimal molecular transport model. Electroneutral Na/H exchange and a cAMP-activated Na+ conductance allow the entry of Na+ from the hemolymph into principal cells. K+ enters via K+ channels. Na+ and K+ are moved across the apical membrane via a hypothetical cation/H exchanger that in turn is driven by the transmembrane H+ electrochemical potential generated by the vacuolar type H+-ATPase located in the apical membrane. The lumen-positive transepithelial voltage generated by transcellular Na+ and K+ secretion drives the transepithelial secretion of Cl– through the paracellular pathway. (B) Minimal electrical transport model that illustrates the active transport pathway through the cell and the passive transport pathway between the cells. Basolateral (bl) and apical (a) membranes are represented by an electromotive force (E) and a resistance (R). The paracellular resistance is represented by the shunt resistance Rsh.





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