ONKEN, H; MOFFETT, SB; MOFFETT, DF; Washington State University; Washington State University; Washington State University: A bioassay to study modulation of transepithelial HCO3– secretion and peristaltic muscle contractions in the anterior stomach of mosquito larvae.
The lumen-negative transepithelial voltage (Vte) of the isolated and perfused anterior stomach of Aedes aegypti larvae was studied with a �semi-open� preparation. In presence of serotonin (0.2 �mol l-1), Vte reflects active, transepithelial HCO3– secretion via a serotonin-stimulated epithelial cell population. In about 25% of the preparations, serotonin-dependent Vte fluctuations (0.2-1.0 mV at a frequency of 1.2-1.5 s-1) are generated during the time-course of the experiments. The frequency and amplitude of these Vte fluctuations evidently reflects peristaltic muscle contractions that can be microscopically observed. The Vte fluctuations may be caused by small pressure changes on transepithelial ion movement induced by the peristaltic muscle contractions. Thus, besides monitoring effects of modulators on transepithelial HCO3– secretion in the anterior stomach, the technique allows simultaneous observations on the influence of modulators on peristaltic muscle contractions in this stomach segment. The first potential modulators studied were Head Peptide I and III, New Head Peptide and Neuropeptide F. Between 10-16 and 10-6 mol l-1 these neuropeptides had no effect or very slightly reduced Vte. However, at 10-8 and 10-6 mol l-1, frequency and amplitude of the Vte fluctuations were reduced by all four peptides in a dose-dependent way. The results show that the head peptides and neuropeptide F act as inhibitory modulators of peristaltic muscle contractions in the anterior stomach of Aedes aegypti larvae, whereas they hardly affect the transepithelial HCO3– secretion involved in stomach alkalization. We gratefully acknowledge donation of the peptides by Dr. M. R. Brown, University of Georgia, and financial support by NSF (IBN-0091208).
