Characterization of the naturally occurring Arg344His variant of the human 5-HT 3A receptor.
The present study aimed at examining the function and pharmacological properties of the naturally occurring Arg344His variant of the human 5-HT(3A) receptor, identified in a schizophrenic patient. In intact human embryonic kidney (HEK) 293 cells expressing the wild-type (WT) or the variant receptor, the function was analyzed by indirect measurement of agonist-induced Ca(2+) current through the 5-HT(3A) receptor channel by an aequorin luminescence-based Ca(2+) assay. In cell membrane patches cation currents were determined electrophysiologically including technically demanding single channel analyses. The pharmacological properties were analyzed by [(3)H]GR65630 binding to cell membrane fragments. The density of [(3)H]GR65630 binding sites in cells expressing the variant receptor was reduced to 55% of that in cells expressing the WT receptor, which, however, was not accompanied by an analogous decrease in 5-HT-induced Ca(2+) influx through the receptor channel. However, the single channel analysis suggests an increase in single receptor channel mean open time (which is known to be subject of many variables) but not in unitary current amplitude. Radioligand competition experiments revealed that the affinity of five 5-HT(3) receptor agonists and four antagonists for the variant receptor did not differ from that for the WT receptor. In conclusion, the variant receptor resembles the WT receptor in that it forms functional homopentameric 5-HT(3A) receptors with identical pharmacological properties. In view of the lack of reduction in Ca(2+) flux through the variant receptor channels in spite of the decrease in its density on the cell membrane, the increase in single receptor channel mean open time appears to compensate for the reduction in variant receptor density.
Combrink
Sandra
S
Institute of Pharmacology and Toxicology, Reuterstr. 2b, University of Bonn, D-53113 Bonn, Germany.
Kostanian
Arevat
A
Walstab
Jutta
J
Barann
Martin
M
Brüss
Michael
M
Göthert
Manfred
M
Bönisch
Heinz
H
D000331:Aequorin / Q000737:chemistry; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004594:Electrophysiology; D014644:Genetic Variation; D006801:Humans; D008163:Luminescent Measurements; D018408:Patch-Clamp Techniques; D011869:Radioligand Assay; D044406:Receptors, Serotonin, 5-HT3 / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D012559:Schizophrenia / Q000235:genetics*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D044406:Receptors, Serotonin, 5-HT3; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D000331:Aequorin; D002118:Calcium