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Samii SI, Webb RA: The stimulatory effect of L-glutamate and related agents on inositol 1,4,5-trisphosphate production in the cestode Hymenolepis diminuta. Comp Biochem Physiol C Pharmacol Toxicol Endocrinol. 1996 Mar;113(3):409-20.
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. |
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