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Characterization of a Novel Serotonin Receptor Subtype (5‐HT ls ) in Rat CNS: Interaction with a GTP Binding Protein
Author(s) -
Zemlan Frank P.,
Schwab Eileen F.
Publication year - 1991
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1991.tb06427.x
Subject(s) - receptor , serotonin , 5 ht receptor , synaptosome , binding site , gtp' , chemistry , biology , microbiology and biotechnology , medicine , biochemistry , in vitro , enzyme
Three pharmacologically distinct high‐affinity [ 3 H]serotonin ([ 3 H]5‐HT) binding sites were identified in spinal cord synaptosomes. [ 3 H]5‐HT competition studies using selective 5‐HT 1A receptor ligands indicated that ∼25% of high‐affinity synaptosomal [ 3 H]5‐HT binding was inhibited by 5‐HT 1A ‐selective compounds, an estimate consistent with [ 3 H](±)‐8‐hydroxy‐2‐(di‐ n ‐propylamino)tetralin([ 3 H]8‐OH‐DPAT) saturation experiments in which 5‐HT 1A receptors were directly labeled. [ 3 H]5‐HT competition studies using high‐affinity 5‐HT 1B compounds performed in the presence of 100 n M 8‐OH‐DPAT (to block 5‐HT 1A receptors) indicated that∼26% of all specific, high‐affinity [ 3 H]5‐HT binding to spinal cord synaptosomes was to 5‐HT 1B receptors. [ 3 H]5‐HT competition studies performed in the presence of 100 n M 8‐OH‐DPAT and 10 n M RU 24969 (to block 5‐HT 1A and 5‐HT 1B receptors, respectively) indicated that the remaining 49% of [ 3 H]5‐HT binding did not possess the phar‐macologic profile previous reported for 5‐HT 1c , 5‐HT 1D , 5‐ HT 1E , 5‐HT 2 , or 5‐HT 3 receptors. This residual 49% of [ 3 H]5‐ HT binding to spinal cord synaptosomes observed in the presence of 100 n M 8‐OH‐DPAT and 10 nM RU 24969 (subsequently referred to as “5‐HT ls ”) displayed high affinity and saturability (K D = 4.7 n M ) in association/dissociation and saturation experiments. Addition of 300 μM GTP or the nonhydrolyzable form of GTP, 5′‐guanylylimidodiphosphate, inhibited [ 3 H]5‐HT binding to 5‐HT 1S receptors in saturation experiments by 35 and 57%, respectively, whereas ATP was without effect. [ 3 H]5‐HT competition studies identified several 5‐HT agonists and antagonists with a high or moderately high affinity for 5‐HT 1s receptors. Although 5‐HT 1s receptors were the predominant 5‐HT 1 receptor subtype present in spinal cord, no significant density of 5‐HT 1s receptors was found in brainstem or frontal cortex.