title: Inhibition of the type 1 inositol 1,4,5-trisphosphate receptor by 2-aminoethoxydiphenylborate.
abstract: 2-Aminoethoxydiphenylborate (2-APB) inhibits the extent of inositol 1,4,5-trisphosphate (InsP(3))-induced Ca(2+) release from cerebellar microsomes with a potency that is dependent upon the InsP(3) concentration used. At high InsP(3) concentrations (10 microM), the concentration of 2-APB required to cause half-maximal InsP(3)-induced Ca(2+) release (IC(50)) was greater than 1 mM, while at 0.25 microM InsP(3) this reduced to 220 microM. The fact that the inhibition of the extent of InsP(3)-induced Ca(2+) release (IICR) by 2-APB was not restored to control levels by high concentrations of InsP(3), in addition to the fact 2-APB did not substantially inhibit [3H]InsP(3) binding to its receptor, indicates that the inhibition is not competitive in nature. Since the cooperativity of IICR as a function of InsP(3) was reduced in the presence of 2-APB (Hill coefficient changing from 1.9 in the absence of 2-APB to 1.4 in the presence of 1 mM 2-APB), this suggests that it is acting as an allosteric inhibitor. 2-APB also reduces the rate constants for IICR. In cerebellar microsomes this release process is biphasic in nature, with a fast and slow phase. 2-APB appears particularly to affect the fast-phase component. Although 2-APB does not inhibit the ryanodine receptor, it does inhibit the Ca(2+) ATPase activity as well store-operated Ca(2+) entry channels, which may limit its use as a specific membrane permeant InsP(3) receptor inhibitor.
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, UK.
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Bilmen
authors.forename: Francesco
authors.initials: F
authors.lastname: Michelangeli
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001896:Boron Compounds / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005057:Eukaryotic Cells / Q000187:drug effects / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism* / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D008024:Ligands; D008861:Microsomes; D011817:Rabbits; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013347:Subcellular Fractions; D013552:Swine
chemical_list: D001896:Boron Compounds; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate; C109986:2-aminoethoxydiphenyl borate; D000252:Calcium-Transporting ATPases; D002118:Calcium