Figure 13. Time-course of the lumen negative transepithelial voltage (V_te) and of the luminal pH (pH_L) recorded with a pH-sensitive microelectrode in the lumen of a preparation of the anterior midgut of larval (4^th instar) Aedes aegypti, showing the effects of repeated luminal perfusion stops in the presence of hemolymph-side serotonin (0.2 μmol l⁻¹).