Postsynaptic target regulates functional responses induced by 5-HT3 serotonin receptors on axonal varicosities of NG108-15 hybrid neuroblastoma cells.
Rat brain presynaptic 5-HT3 serotonin receptors, members of the ligand-gated ion channel superfamily, induce changes in nerve terminal [Ca2+]i in a manner distinct from that found for somatic 5-HT3 receptors. Here, we assessed the role of postsynaptic target in regulating the nature of presynaptic receptor-induced responses, using the hybrid neuroblastoma cell line NG108-15 as a model neuronal system that expresses 5-HT3 receptors. Using immunocytochemistry, 5-HT3 receptors were found to be present on the presynaptic-like varicosities of differentiated NG108-15 cells, indicating that these receptors possess an inherent ability to localize to potential presynaptic sites. In the absence of postsynaptic target, 5-HT3 receptors localized to the varicosities induce rapid but transient changes in [Ca2+]i that were initiated by voltage-gated Ca2+ channels, as assessed using Ca2+ channel blockers, these properties being typical of those found for somatic 5-HT3 receptors. In co-cultures containing rat myotubes, with which NG108-15 cells form functional cholinergic synapses, the 5-HT3 receptor-induced changes in [Ca2+]i in the axonal varicosities shifted over time (three to 10 days) to that found for brain nerve endings: sustained responses that were insensitive to blockade by antagonists of voltage-gated Ca2+ channels. The effect of co-culturing myotubes with the NG108-15 cells was mimicked by conditioned media from myotube cultures. These results indicate that regulatory molecules from the target postsynaptic cell dictate the functional responses elicited by presynaptic 5-HT3 receptors. Because the target-induced changes required several days before they were evident, we hypothesize that changes in protein expression, perhaps the consequence of altered gene regulation, underlie the changes in the responses to 5-HT3 receptor activation in the axonal varicosities of this neuronal cell line.
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Departments of Pharmacology & Physiology and Neurobiology & Anatomy, Medical College of Pennsylvania/Hahnemann University, Philadelphia, PA 19102, USA.
Nichols
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D000818:Animals; D001369:Axons / Q000378:metabolism*; D001645:Biguanides / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D018920:Coculture Techniques; D017077:Culture Media, Conditioned / Q000494:pharmacology; D006822:Hybrid Cells / Q000378:metabolism / Q000648:ultrastructure; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D009447:Neuroblastoma; D009474:Neurons / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D011985:Receptors, Serotonin / Q000378:metabolism*; D044406:Receptors, Serotonin, 5-HT3; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000648:ultrastructure
D001645:Biguanides; D017077:Culture Media, Conditioned; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D017366:Serotonin Receptor Agonists; C065734:1-(3-chlorophenyl)biguanide; D002118:Calcium