Isothiocyanatobenzyl imidazoline is an alkylating agent for I2-imidazoline binding sites in rat and rabbit tissues.
Isothiocyanatobenzyl imidazoline (IBI), the 4'-NCS analogue of tolazoline, has been used to alkylate several receptor sites in rabbit iris muscles. Because of the high affinity of tolazoline for the I2-imidazoline binding sites (Ki = 16-130 nM), this study was designed to assess whether IBI is also an alkylating agent for these sites. In competition studies, IBI displayed moderate affinity (Ki approximately 2-3 microM) against I2A-imidazoline sites in the rabbit cerebral cortex and I2B-imidazoline sites in the rat cerebral cortex labelled by [3H]2-(2-benzofuranyl)-2-imidazoline ([3H]2-BFI). However, preincubation (30 min at 25 degrees C) of rat cortical and liver membranes with IBI (10(-7) M to 10(-3) M), followed by extensive washing, markedly decreased (17% to 96%) the specific binding of [3H]2-BFI to I2B-imidazoline sites. IBI (10(-5) M to 10(-3) M) also bound irreversibly to I2A-imidazoline sites in rabbit cerebral cortex but with a lesser efficacy (27% to 83% reduction of [3H]2-BFI binding). Saturation curves of [3H]2-BFI binding in the rat cerebral cortex indicated that preincubation with 10(-6) M IBI reduced the total density (Bmax) without affecting the affinity (Kd) of I2B-imidazoline sites for IBI. Acute treatments (6 h) with IBI (10 and 30 mg/kg, i.p.) also dose-dependently reduced (26% and 41%; respectively) the total density of I2B-imidazoline sites. These results demonstrate the ability of IBI to alkylate I2-imidazoline binding sites in vitro and in vivo and provide evidence for the use of IBI as a new tool for the study of the functional implications of imidazoline binding sites.
Boronat
M A
MA
Institute of Neurobiology Ramón y Cajal, CSIC, Department of Biology, University of the Balearic Islands, Palma de Mallorca, Spain.
Olmos
G
G
Miller
D D
DD
Patil
P N
PN
García-Sevilla
J A
JA
D000345:Affinity Labels / Q000494:pharmacology; D000818:Animals; D001572:Benzofurans / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D014043:Tolazoline / Q000031:analogs & derivatives* / Q000494:pharmacology
D000345:Affinity Labels; D001572:Benzofurans; D007093:Imidazoles; C071242:2-(4'-isothiocyanatobenzyl)imidazoline; C103723:2-(2-benzofuranyl)-2-imidazoline; D014043:Tolazoline