title: Autoradiographic localization and characterization of [3H]alpha-trinositol (1D-myo-inositol 1,2,6-trisphosphate) binding sites in human and mammalian tissues.
abstract: alpha-Trinositol (1D-myo-inositol 1,2,6-trisphosphate, PP56) selectively and potently inhibits the vasoconstrictor effects of neuropeptide Y (NPY). The authors used quantitative in vitro receptor autoradiography to localize and characterize [3H]alpha-trinositol binding sites in human and mammalian tissues. [3H]alpha-trinositol bound specifically to vascular and nonvascular smooth muscle in human, porcine and rat tissues. Binding was time dependent, reversible, saturable and specific for alpha-trinositol compared with inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate (Ins-1,3,4,5-P4) and inositol hexakisphosphate (Ins-P6). Binding to each structure gave Kd values of 5 to 20 nM and was consistent with a homogeneous population of sites. Binding was optimal at pH 5 and at low calcium concentrations. Comparison with [125I]Bolton Hunter-labeled NPY ([125I]BH-NPY) binding in porcine tissues revealed 1) a partial colocalization but Bmax values for [3H]alpha-trinositol binding some two orders of magnitude higher than for [125I]BH-NPY and 2) failure of each of the two ligands to inhibit binding of the other. Comparison of [3H]alpha-trinositol with [3H]Ins-1,3,4,5-P4 binding in human umbilical cord revealed that both ligands bound specifically to vascular smooth muscle but that only [3H]Ins-1,3,4,5-P4 bound to arterial endothelium. Both ligands bound to sites with rank orders of affinity Ins-1,3,4,5-P4 > Ins-P6 > inositol 1,4,5-trisphosphate. alpha-Trinositol had, however, three orders of magnitude higher affinity for [3H]alpha-trinositol than [3H]Ins-1,3,4,5-P4 binding sites; Ins-1,3,4,5-P4 and Ins-P6 had higher affinity for [3H]Ins-1,3,4,5-P4 binding sites. Specific [3H]alpha-trinositol binding sites may represent receptors by which alpha-trinositol inhibits NPY effects on vascular tone.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Inflammation Group, London Hospital, United Kingdom.
authors.forename: D A
authors.initials: DA
authors.lastname: Walsh
authors.forename: P I
authors.initials: PI
authors.lastname: Mapp
authors.forename: J M
authors.initials: JM
authors.lastname: Polak
authors.forename: D R
authors.initials: DR
authors.lastname: Blake
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000378:metabolism*; D001345:Autoradiography; D001665:Binding Sites; D003106:Colon / Q000378:metabolism; D005260:Female; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D009478:Neuropeptide Y / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013154:Spleen / Q000378:metabolism; D013552:Swine; D013583:Synovial Membrane / Q000378:metabolism; D014470:Umbilical Cord / Q000378:metabolism
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D007295:Inositol Phosphates; D009478:Neuropeptide Y; C081655:inositol-1,3,4,5-tetrakisphosphate; C059368:atrinositol