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First published online September 15, 2004
Journal of Experimental Biology 207, 3731-3739 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01208

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The anterior stomach of larval mosquitoes (Aedes aegypti): effects of neuropeptides on transepithelial ion transport and muscular motility

H. Onken^*, S. B. Moffett and D. F. Moffett

School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA

View larger version (13K): [in a new window]   Fig. 1. Schematic representation of the set-up for the measurement of the transepithelial voltage with a semi-open preparation of stomach segments of larval mosquitoes. The luminal perfusion (PL) is achieved by connection of the perfusion pipette to a push-pull multi-speed syringe pump. The direction of the perfusion can be changed by connection to the infusion syringe or the withdrawal syringe. Bath perfusion (PB) is by gravity flow from interchangeable reservoirs with oxygenated salines. The transepithelial voltage is measured with calomel electrodes connected to the pipette (VL) and the bath (VB) by agar bridges. D, drainage.

View larger version (15K): [in a new window]   Fig. 2. Representative time-course of the transepithelial voltage (Vte) across the anterior stomach of larval A. aegypti, showing the initial voltage decrease after mounting the anterior stomach, the voltage stimulation induced by serotonin (0.2 µmol l–1), and the effects of Aedae-AST-A 1–5 (example of N=5).

View larger version (9K): [in a new window]   Fig. 3. Transepithelial voltages (Vte) expressed as percentage of the control voltage (100%) for different concentrations of Aedae-AT (open circles; control voltage –27±4 mV, N=5), Aedae-HP-I (filled circles; control voltage –27±4 mV, N=8), Aedae-HP-III (filled squares; control voltage –37±10 mV, N=6), and Aedae-sNPF (filled triangles; control voltage –43±11 mV, N=5). All values are means. Selected error bars in the figure reflect S.E.M.

View larger version (9K): [in a new window]   Fig. 4. Transepithelial voltages (Vte) expressed as percentage of the control voltage (100%) for different concentrations of Aedae-NPF (filled circles; control voltage –32±6 mV, N=9) and proctolin (open diamonds; control voltage –37±5 mV, N=6). Values are means + or – S.E.M. Asterisks indicate significant difference from the control (P<0.05).

View larger version (16K): [in a new window]   Fig. 5. (A) Examples for the different patterns of voltage fluctuations observed with isolated and perfused anterior stomach preparations of larval A. aegypti. (B) Representative example of the recordings of voltage fluctuations of the anterior stomach of A. aegypti larvae, showing their dependence on the presence of serotonin (N=7). Upper trace recorded in presence of serotonin (0.2 µmol l–1), middle trace after its washout, and lower trace after re-establishing serotonin. (C) Representative example of the recordings of voltage fluctuations in absence of Aedae-HP-I and in presence of different concentrations of the peptide (N=5). Voltage traces from top to bottom: control, Aedae-HP-I 10–8 mol l–1; Aedae-HP-I 10–6 mol l–1; control after washout of Aedae-HP-I.

View larger version (22K): [in a new window]   Fig. 6. Amplitudes of voltage fluctuations in presence of neuropeptides related to the control with 0.2 µmol l–1 serotonin only (AExp/ASer). Aedae-HP-I (bars with dots, N=7, + S.E.M.), Aedae-HP-III (bars with vertical lines, N=7, + S.E.M.), Aedae-sNPF (bars with horizontal lines; N=5, + S.E.M.), Aedae-NPF (bars with diagonal lines, N=7, + S.E.M.). Each peptide was applied at 10–8 and 10–6 mol l–1. *Significant difference from the control (P<0.05); **significant difference from the lower peptide concentration (P<0.05) in addition to the difference from the control.

View larger version (26K): [in a new window]   Fig. 7. Sketch summarizing the effects of neuropeptides on ion transport across the epithelial cell layer (E) and peristaltic activity of the muscle layer (M) of the anterior stomach of larval A. aegypti. + denotes stimulative and inhibitory effects on epithelial and/or muscle layers of the anterior stomach tissue.