ABSTRACT
The effects of L-glutamate, acetylcholine, and serotonin (5HT) were examined on generation of inositol 1,4,5-triphosphate [Ins(1,4,5)P3], in membrane preparations of the cestode Hymenolepis diminuta. Only L-glutamate and acetylcholine stimulated a significant elevation in Ins(1,4,5)P3. The response to L-glutamate was stereospecific; D-glutamate or L-aspartate were not as potent. A role for G-protein(s) was supported by the observations that sodium fluoride stimulated Ins(1,4,5)P3 generation, and the L-glutamate response was potentiated by GTP and GTP-S and was suppressed by GDPS. However, studies with pertussis and cholera toxins indicated that the putative G-protein(s) was not pertussis or cholera toxin sensitive. The pharmacological profile of the L-glutamate response was examined partially. Trans-ACPD was a very effective agonist at 10(-5)M. While 10(-3)M L-glutamate, NMDA, and AMPA significantly elevated Ins(1,4,5)P3 levels, quisqualate and kainate did not. The elevation of Ins(1,4,5)P3 levels by L-glutamate and NMDA was antagonized by the specific glutamatergic antagonists AP-5, AP-7, CNQX, and CPP. While the response to ACPD was antagonized by AP5, CPP and CPG, CNQX was without effect. Collectively, the data support the hypothesis that in the cestode H. diminuta, L-glutamate activation of a metabotropic (ACPD) and/or ionotropic-like AMPA/NMDA receptor subtypes proceeds via a G protein(s) to enhance phospholipase C activity, ultimately resulting in the elevation of Ins(1,4,5)P3 levels in the tissues.
Subject(s)
Glutamic Acid/pharmacology , Hymenolepis/drug effects , Hymenolepis/metabolism , Inositol 1,4,5-Trisphosphate/biosynthesis , Acetylcholine/pharmacology , Adenine Nucleotides/pharmacology , Animals , Calcium/pharmacology , Cell Membrane/drug effects , Cell Membrane/metabolism , Cholera Toxin/pharmacology , Culture Media , GTP-Binding Proteins/physiology , Guanine Nucleotides/pharmacology , Serotonin/pharmacology , Sodium Fluoride/pharmacology , Virulence Factors, Bordetella/pharmacologyABSTRACT
The localization of acetylcholine in tissues of the cestode Hymenolepis diminuta was determined, following derivatization, using an antibody raised against choline-glutaraldehyde-protein. Specific immunoreactivity was observed in the rostellum and beneath the suckers of the scolex, in the longitudinal nerve cords, in cells adjacent to some deep longitudinal muscles, in the genital primordium, in the wall of the cirrus sac, and in the external and internal seminal vesicle. The distribution of acetylcholine-like immunoreactivity in relation to that of serotonin and glutamate, and the distribution of acetylcholinesterase in H. diminuta is discussed.
