Comparison of [125I]iodolysergic acid diethylamide binding in human frontal cortex and platelet tissue.
The human platelet contains a functional 5-hydroxytryptamine (5-HT) receptor that appears to resemble the 5-HT2 subtype. In this study, we have used the iodinated derivative [125I]iodolysergic acid diethylamide ([125I]iodoLSD) in an attempt to label 5-HT receptors in human platelet and frontal cortex membranes under identical assay conditions to compare the sites labelled in these two tissues. In human frontal cortex, [125I]iodoLSD labelled a single high-affinity site (KD = 0.35 +/- 0.02 nM). Displacement of specific [125I]iodoLSD binding indicated a typical 5-HT2 receptor inhibition profile, which demonstrated a significant linear correlation (r = 0.97, p less than 0.001, n = 17) with that observed using [3H]ketanserin. However, [125I]iodoLSD (Bmax = 136 +/- 7 fmol/mg of protein) labelled significantly fewer sites than [3H]ketanserin (Bmax = 258 +/- 19 fmol/mg of protein) (p less than 0.001, n = 6). In human platelet membranes, [125I]iodoLSD labelled a single site with affinity (KD = 0.37 +/- 0.03 nM) similar to that in frontal cortex. The inhibition profile in the platelet showed significant correlation with that in frontal cortex (r = 0.96, p less than 0.001, n = 16). We conclude that the site labelled by [125I]iodoLSD in human platelet membranes is biochemically similar to that in frontal cortex and most closely resembles the 5-HT2 receptor subtype, although the discrepancy in binding capacities of [125I]iodoLSD and [3H]ketanserin raises a question about the absolute nature of this receptor.
Elliott
J M
JM
Department of Pharmacology and Toxicology, St. Mary's Hospital Medical School, London, England.
Kent
A
A
D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005625:Frontal Lobe / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D007650:Ketanserin / Q000378:metabolism; D007700:Kinetics; D008238:Lysergic Acid Diethylamide / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000097:blood / Q000378:metabolism
D007457:Iodine Radioisotopes; C039496:2-iodolysergic acid diethylamide; D008238:Lysergic Acid Diethylamide; D007650:Ketanserin