ABSTRACT
The Malpighian (renal) tubule of Drosophila melanogaster is a useful model for studying epithelial transport. The purpose of this study was to identify factors responsible for modulating transepithelial chloride conductance in isolated tubules. I have found that tyrosine and several of its metabolites cause an increase in chloride conductance. The most potent of these agonists is tyramine, which is active at low nanomolar concentrations; the pharmacology of this response matches that of the previously published cloned insect tyramine receptor. In addition, the tubule appears capable of synthesizing tyramine from applied tyrosine, as shown by direct measurement of tyrosine decarboxylase activity. Immunohistochemical staining of tubules with an antibody against tyramine indicates that the principal cells are the sites of tyramine production, whereas previous characterization of the regulation of chloride conductance suggests that tyramine acts on the stellate cells. This is the first demonstration of a physiological role for an insect tyramine receptor.
Subject(s)
Cell Membrane Permeability/physiology , Chlorides/metabolism , Drosophila melanogaster/metabolism , Epithelial Cells/metabolism , Ion Transport/physiology , Kidney Tubules/metabolism , Receptors, Biogenic Amine/metabolism , Tyramine/biosynthesis , Animals , Biological Clocks/drug effects , Biological Clocks/physiology , Cell Membrane/drug effects , Cell Membrane/metabolism , Dose-Response Relationship, Drug , Drosophila melanogaster/cytology , Epithelial Cells/cytology , Epithelial Cells/drug effects , Immunohistochemistry , Ion Transport/drug effects , Kidney Tubules/cytology , Kidney Tubules/drug effects , Membrane Potentials/drug effects , Membrane Potentials/physiology , Receptors, Biogenic Amine/agonists , Receptors, Biogenic Amine/antagonists & inhibitors , Tyramine/agonists , Tyramine/antagonists & inhibitors , Tyrosine/agonists , Tyrosine/analogs & derivatives , Tyrosine/biosynthesis , Yohimbine/pharmacologyABSTRACT
Three-dimensional pharmacophore hypotheses were built from a set of 36 octopamine (OA)/tyramine (TA) agonists responsible for the inhibition of sex-pheromone production in Plodia interpunctella. Among the ten chemical-featured models generated by a program Catalyst/Hypo, hypotheses including hydrogen-bond acceptor (HBA), hydrogen-bond acceptor aliphatic (HBAl), hydrophobic (Hp), hydrophobic aromatic (HpAr) and hydrophobic aliphatic (HpAl) features were considered to be important and predictive in evaluating OA/TA agonists. Active agonists mapped well onto all the features of the hypothesis such as HBA, HBAl, Hp, HpAr and HpAl features. On the other hand, inactive compounds were shown to be poorly capable of achieving an energetically favorable conformation shared by the active molecules in order to fit the 3-D chemical-feature pharmacophore models. Those hypotheses are considered to be used in designing new leads for hopefully more active compounds. Further research on the comparison of models from the agonists may help elucidate the mechanisms of OA/TA receptor-ligand interactions.