Identification of lymphocyte 5-HT3 receptor subtype and its implication in fish T-cell proliferation.
In the present study, we identified the serotonergic receptor of type 3 (5-HT3) on the lymphocytes of a teleost fish, Oncorhynchus mykiss. In the pharmacological studies on the binding of [3H]serotonin to membrane receptor sites, 2-methyl-5-HT, an agonist of 5-HT3 receptors, displaced the binding of [3H]serotonin to fish lymphocytes, indicating the presence of 5-HT3 receptors on these cells. The known antagonists of the mammalian 5-HT3 receptor, ICS-205-930 and metoclopramide, failed to displace [3H]serotonin binding to lymphocytes during the period of association equilibrium (8 min); however, these antagonists progressively displaced [3H]serotonin binding from 10 to 40 min of incubation. These results suggest that fish 5-HT3 lymphocyte receptors may differ pharmacologically from mammalian receptors. As mammalian 5-HT3 receptors are coupled with Na+ inward movements, we undertook a study on Na+ influx by using SBFI/AM, a fluorescent probe. In SBFI/AM loaded fish lymphocytes, 2-methyl-5-HT leaked Na+ inward movements. Prior incubation of lymphocytes for 30 min in the presence of 5-HT3 antagonists, ICS-205-930, metoclopramide and MDL-72222, curtailed significantly the Na+ influx evoked by 2-methyl-5-HT, demonstrating that Na+ is leaked into fish lymphocytes via the 5-HT3 receptor-channel whose functioning is blocked by these antagonists. Furthermore, 2-methyl-5-HT exerted immunosuppressive effects in a dose dependent manner on fish T-lymphocytes stimulated by phytohaemagglutinin (PHA). Serotonin and 2-methyl-5-HT blocked the cell cycle progression of PHA-stimulated T-cells from G0/G1 to S phase. The immunosuppressive effects of 2-methyl-5-HT on T-cells were partially reversed by the antagonists, metoclopramide and ICS-205-930; however, the latter antagonist at high concentrations synergized with the immunosuppressive effects of 2-methyl-5-HT. These results demonstrate that the fish lymphocyte 5-HT3 receptor, which may be pharmacologically different from mammalian receptor subtype, is functionally implicated in fish T-cell proliferation.
Meyniel
J P
JP
Laboratoire de Physiologie Animale, Faculté des Sciences de Limoges, France.
Khan
N A
NA
Ferrière
F
F
Deschaux
P
P
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D007211:Indoles / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000502:physiology*; D008214:Lymphocytes / Q000737:chemistry* / Q000378:metabolism; D008787:Metoclopramide / Q000494:pharmacology; D017686:Oncorhynchus mykiss / Q000276:immunology*; D010835:Phytohemagglutinins / Q000494:pharmacology; D011985:Receptors, Serotonin / Q000737:chemistry* / Q000378:metabolism*; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin / Q000031:analogs & derivatives / Q000502:physiology; D012702:Serotonin Antagonists / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013997:Time Factors; D014316:Tritium; D014326:Tropanes / Q000494:pharmacology; D000077526:Tropisetron
D007211:Indoles; D010835:Phytohemagglutinins; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists; D014326:Tropanes; D014316:Tritium; D012701:Serotonin; D000077526:Tropisetron; C045918:2-methyl-5-HT; D012964:Sodium; D008787:Metoclopramide; C042253:bemesetron