Figure 9. Mean lumen negative transepithelial voltages (V_te; - S.E.M.) of 9 anterior midguts stimulated with serotonin (0.2 μmol l⁻¹) before (white bar) and after (grey bar) substituting hemolymph-side Na⁺ and photographs of a representative preparation of the anterior midgut of larval (4^th instar) Aedes aegypti identical times after perfusion stop in presence (left) and absence (right) of Na⁺ in the hemolymph-side saline. The tissues were exposed for an average of 30 minutes to Na⁺-free saline before V_te and alkalinization after the influence of the manipulation were recorded. Asterisk: Mean V_te significantly different from the control (P < 0.05).