Characteristics of [3H]5-hydroxytryptamine binding to iris-ciliary body tissue of the rabbit.
OBJECTIVE
This study sought to identify, characterize, and localize subtypes of 5-hydroxytryptamine (HT) receptors in rabbit iris-ciliary body.


METHODS
Radioligand binding assays were performed with [3H]5-hydroxytryptamine on membranes prepared from rabbit iris-ciliary bodies and on tissue sections subsequently developed by autoradiography.


RESULTS
[3H]5-HT appeared to bind to a single population of receptors in membrane preparations of rabbit iris-ciliary body. The apparent affinity of the ligand (KD) was 2.19 nM, and the density of binding sites was 58.3 fmol/mg protein. Binding of [3H] 5-HT exhibited guanosine-5-triphosphate sensitivity. Competitive inhibition experiments were performed to differentiate between 5-HT receptor subtypes. A relative potency order of 5-CT > 5-HT = 8-OH-DPAT > ipsapirone > RU24969 > sumatriptan > ritanserin > ketanserin was demonstrated. The apparent inhibitory constants for the ligands tested fit with the profile expected of binding to 5-HT1A receptors. Inhibition studies with [3H] 5-HT plus 100 nM 8-OH-DPAT (which inhibits binding to 5-HT1A receptors only) representing total binding, indicated that no further displacement occurred when ligands preferentially selective for 5-HT1B, 5-HT1D alpha,1D beta, or 5-HT2C were tested. Total binding of [3H] 5-HT in tissue sections developed by autoradiography was displaced completely by 100 nM 8-OH-DPAT. Melatonin showed little affinity for the [3H] 5-HT binding sites.


CONCLUSIONS
A population of 5-HT1A receptors is present in rabbit ciliary processes. There is no evidence to suggest the presence of 5-HT1D alpha, 5-HT1D beta, 5-HT2B, or 5-HT2C receptors in the iris-ciliary body.
Chidlow
G
G
Nuffield Laboratory of Ophthalmology, University of Oxford, United Kingdom.
De Santis
L M
LM
Sharif
N A
NA
Osborne
N N
NN
D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002924:Ciliary Body / Q000378:metabolism*; D007498:Iris / Q000378:metabolism*; D008550:Melatonin / Q000494:pharmacology; D011817:Rabbits; D011869:Radioligand Assay; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D008550:Melatonin