Molecular properties of the papaverine binding sites identified in human colonic membranes with 6,7-dimethoxy-4-(4'-amino,3'-[125I]iodobenzyl) isoquinoline as probe.
The binding sites for papaverine in human intestine were studied with the radioiodinated papaverine derivative, 6,7-dimethoxy-4-(4'-amino,3'-[125I]iodobenzyl)isoquinoline [( 125I]DMABI) as a probe. This drug was shown to bind to two specific binding sites in human colon membranes; one with a low capacity (Kd = 0.02 +/- 0.01 microM, Bmax = 0.77 +/- 0.15 fmol/mg) and another with a high capacity (Kd = 12 +/- 1.5 microM, Bmax = 167 +/- 20 fmol/mg). The ability of various 4-benzyl isoquinolines derivatives, to inhibit radioligand binding was not influenced by 4'-substitutions, but was influenced by 6,7-substitutions, e.g. 6-hydroxy greater than 7-hydroxy greater than 6,7-dihydroxy; and by other substitutions, e.g. 1-CH3 greater than N-oxyde. The papaverine probe was further used to examine structural aspects of human colon papaverine binding sites. For this purpose, [125I]DMABI-labeled membranes were irradiated with U.V. for 15 min at 4 degrees C. Subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis of membranes revealed a major, specifically labeled protein of Mr = 36,000 Da. This photoaffinity labeling was protected by unlabeled DMABI in a dose-dependent manner (IC50: 0.5 microM).
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INSERM U 178, Différenciation et Neuroendocrinologie de Cellules Digestives, Villejuif, France.
Christinaki
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D000345:Affinity Labels; D000818:Animals; D001667:Binding, Competitive; D003106:Colon / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010208:Papaverine / Q000031:analogs & derivatives* / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D000345:Affinity Labels; C050314:6,7-dimethoxy-4-(4'-amino-3'-iodobenzyl)isoquinoline; D010208:Papaverine