Characterization of a novel /sup 3/H-5-hydroxytryptamine binding site subtype in bovine brain membranes
/sup 3/H-5-Hydroxytryptamine (5-HT) binding sites were analyzed in bovine brain membranes. The addition of either the 5-HT1A-selective drug 8-OH-DPAT (100 nM) or the 5-HT1C-selective drug mesulergine (100 nM) to the assay resulted in a 5-10% decrease in specific /sup 3/H-5-HT binding. Scatchard analysis revealed that the simultaneous addition of both drugs decreased the Bmax of /sup 3/H-5-HT binding by 10-15% without affecting the KD value (1.8 +/- 0.3 nM). Competition studies using a series of pharmacologic agents revealed that the sites labeled by /sup 3/H-5-HT in bovine caudate in the presence of 100 nM 8-OH-DPAT and 100 nM mesulergine appear to be homogeneous. 5-HT1A selective agents such as 8-OH-DPAT, ipsapirone, and buspirone display micromolar affinities for these sites. RU 24969 and (-)pindolol are approximately 2 orders of magnitude less potent at these sites than at 5-HT1B sites which have been identified in rat brain. Agents displaying nanomolar potencies for 5-HT1C sites such as mianserin and mesulergine are 2-3 orders of magnitude less potent at the /sup 3/H-5-HT binding sites in bovine caudate. In addition, both 5-HT2- and 5-HT3-selective agents are essentially inactive at these binding sites. These /sup 3/H-5-HT sites display nanomolar affinity for 5-carboxyamidotryptamine, 5-methoxytryptamine, metergoline, and 5-HT. Apparent Ki values of 10-100 nM are obtained for d-LSD, RU 24969, methiothepin, tryptamine, methysergide, and yohimbine, whereas I-LSD and corynanthine are significantly less potent. In addition, these /sup 3/H-5-HT labeled sites are regulated by guanine nucleotides and calcium. Regional studies indicate that this class of sites is most dense in the basal ganglia but exists in all regions of bovine brain. These data therefore demonstrate the presence of a homogeneous class of 5-HT1 binding sites in bovine caudate that is pharmacologically distinct from previously defined 5-HT1A, 5-HT1B, 5-HT1C, 5-HT2, and 5-HT3 receptor subtypes. (Abstract Truncated)
- Research Organization:
- Stanford Univ. Medical Center, CA
- OSTI ID:
- 6620321
- Journal Information:
- J. Neurosci.; (United States), Vol. 3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BRAIN
BIOCHEMISTRY
SEROTONIN
BIOCHEMICAL REACTION KINETICS
CALCIUM
CATTLE
MEMBRANES
NUCLEOTIDES
RECEPTORS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ALKALINE EARTH METALS
AMINES
ANIMALS
AROMATICS
AUTONOMIC NERVOUS SYSTEM AGENTS
AZAARENES
AZOLES
BODY
CENTRAL NERVOUS SYSTEM
CHEMISTRY
DOMESTIC ANIMALS
DRUGS
ELEMENTS
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
INDOLES
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
MAMMALS
MEMBRANE PROTEINS
METALS
NERVOUS SYSTEM
NEUROREGULATORS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
PROTEINS
PYRROLES
RADIOPROTECTIVE SUBSTANCES
REACTION KINETICS
RUMINANTS
SYMPATHOMIMETICS
TRYPTAMINES
VERTEBRATES
550201* - Biochemistry- Tracer Techniques