5-HT3 receptors induce rises in cytosolic and nuclear calcium in NG108-15 cells via calcium-induced calcium release.
A complete understanding of how excitatory ligand-gated ion channels regulate intracellular Ca2+ in nerve cells remains to be elucidated. Laser-scanning confocal microscopy was used here to measure Ca2+ changes in the neuroblastoma x glioma hybrid cell line NG108-15, employed as a model nerve cell line, upon activation by the 5-HT3 receptor, a serotonin-activated ligand-gated ion channel. Addition of the 5-HT3 agonist 1-m-(chlorophenyl)-biguanide (mCPBG) induced increases in [Ca2+]i in both the cytoplasm and the nuclei of the NG108-15 cells. Using high-time resolution line scanning, no delay was evident between the mCPBG-induced rise in cytosolic [Ca2+]i and the rise in nuclear [Ca2+]i. The agonist-induced responses were completely blocked by addition of EGTA to chelate external Ca2+ and by addition of the 5-HT3 receptor antagonist tropisetron or the L-type Ca2+ channel blocker nitrendipine. Caffeine, but not thapsigargin, treatment significantly reduced the mCPBG-induced responses in the nucleus and the cytoplasm, both to the same extent. We conclude that, upon 5-HT3 receptor activation, Ca2+ enters the cells through voltage-gated Ca2+ channels and then triggers the release of Ca2+ from ryanodine-sensitive intracellular stores, greatly amplifying the increases in Ca2+ in the cytoplasm and the nucleus.
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Department of Pharmacology and Neurobiology, MCP Hahnemann School of Medicine, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania 19129, USA.
Nichols
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D001645:Biguanides / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006822:Hybrid Cells; D011985:Receptors, Serotonin / Q000378:metabolism*; D044406:Receptors, Serotonin, 5-HT3; D017366:Serotonin Receptor Agonists / Q000378:metabolism / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D001645:Biguanides; D015220:Calcium Channels; D011985:Receptors, Serotonin; D044406:Receptors, Serotonin, 5-HT3; D017366:Serotonin Receptor Agonists; C065734:1-(3-chlorophenyl)biguanide; D002118:Calcium