Characterization of [3H]meta-chlorophenylbiguanide binding to 5-HT3 receptors in N1E-115 neuroblastoma cells.
The binding characteristics of a radiolabelled 5-HT3 receptor agonist, [3H]meta-chlorophenylbiguanide (mCPBG), were examined in membranes from N1E-115 neuroblastoma cells. Scatchard plots of saturation binding data showed the presence of two populations of binding sites, with Kd = 0.03 +/- 0.01 nM and 4.4 +/- 1.2 nM and Bmax = 11.9 +/- 4.2 and 897.9 +/- 184.7 fmol/mg protein respectively. Competition studies with a selection of agonists and antagonists revealed the pharmacological profile expected for a 5-HT3 receptor. The rank order of potency for antagonists was granisetron > quipazine > GR65630 > ondansetron > MDL72222, and for agonists was mCPBG > 5-HT (5-hydroxytryptamine, serotonin) > 2-methyl-5-HT. IC50 values for 5-HT and 2-methyl-5-HT were lower than those observed using radiolabelled antagonists, and combined with functional experiments, the data suggest that [3H]mCPBG may label high affinity desensitized states of the receptor. We conclude that [3H]mCPBG labels 5-HT3 receptors in N1E-115 neuroblastoma cell membranes and may be a useful compound with which to explore 5-HT3 receptors in other systems.
Lummis
S C
SC
LMB Neurobiology Division, MRC Centre, Cambridge, UK.
Sepúlveda
M I
MI
Kilpatrick
G J
GJ
Baker
J
J
D000818:Animals; D001645:Biguanides / Q000378:metabolism*; D001667:Binding, Competitive; D004594:Electrophysiology; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism*; D011869:Radioligand Assay; D011985:Receptors, Serotonin / Q000378:metabolism*; D014316:Tritium; D014407:Tumor Cells, Cultured
D001645:Biguanides; D011985:Receptors, Serotonin; D014316:Tritium; C065734:1-(3-chlorophenyl)biguanide