Introduction of the 5-HT3B subunit alters the functional properties of 5-HT3 receptors native to neuroblastoma cells

The identification of a second 5-HT3 (5-HT3B) Subunit provides an explanation for 5-HT1 receptor heterogeneity. We investigated whether introduction of recombinant 5-HT3B subunits would alter the functional properties of mouse neuroblastoma 5-HT3 receptors. RT-PCR analysis revealed that NB41A3 cells contain mRNAs encoding 5-HT3A and 5-HT3B subunits. 5-HT increased intracellular Ca2+ concentration ([Ca2+](i)) and caused the concentration-dependent activation of inward current,, recorded at -60 mV. Both actions of 5-HT were antagonized by ondansetron. The 5-HT concentration-response relationship of NB41A3 cells was indistinguishable from that of the related NG108-15 cell line. The selective 5-HT3-receptor agonist mCPBG also elevated [Ca2+], and activated inward currents. 2-M-5HT was less efficacious than 5-HT as an activator of 5-HT3 receptors in NB41A3 cells and did not significantly increase [Ca2+](i). The 5-HT induced increase in [Ca-2a](i) did not involve caffeine- or thapsigargin-sensitive intracellular stores. The introduction of the 5-HT3B subunit by transient transfection of NB41A3 cells caused 5-HT to become less potent as an activator of 5-HT3 receptors and altered the kinetics of 5-HT activated currents so that they resembled currents mediated by 5-HT3AB receptors. The 5-HT3B subunit also abolished the 5-HT induced [Ca2+](i) increase seen in untransfected NB41A3 cells. These data are consistent with the hypothesis that NB41A3 cells predominantly express homomeric 5-HT3A receptors that become heteromeric 5-HT3AB receptors upon introduction of the recombinant 5-HT3B subunit. (C) 2003 Elsevier Science Ltd. All rights reserved.