RT Journal Article
SR Electronic
T1 Identification of partial agonists with low intrinsic activity at the inositol-1,4,5-trisphosphate receptor.
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 499
OP 503
VO 43
IS 4
A1 S T Safrany
A1 R A Wilcox
A1 C Liu
A1 D Dubreuil
A1 B V Potter
A1 S R Nahorski
YR 1993
UL http://molpharm.aspetjournals.org/content/43/4/499.abstract
AB The interactions of synthetic L-chiro-inositol-2,3,5-trisphosphorothioate [L-ch-Ins(2,3,5)PS3] and D-6-deoxy-myo-inositol-1,4,5-trisphosphorothioate [D-6-deoxy-Ins(1,4,5)PS3] with D-myo-inositol-1,4,5-trisphosphate [Ins(1,4,5)P3] receptors have been examined using radioligand binding assays and Ca2+ mobilization from permeabilized SH-SY5Y cells. The ability of these analogues to compete with [3H]Ins(1,4,5)P3 for specific sites on adrenal cortical membranes indicated that, although weaker than Ins(1,4,5)P3, both ligands competed fully for these sites [L-ch-Ins(2,3,5)PS3,Ki = 0.5 microM; D-6-deoxy-Ins(1,4,5)PS3,Ki = 5.3 microM]. However, in assays examining the amount of Ca2+ mobilized from the stores of permeabilized SH-SY5Y cells, both of these synthetic analogues displayed low intrinsic activity [L-ch-Ins(2,3,5)PS3, 34%; D-6-deoxy-Ins(1,4,5)PS3, 42% of that of Ins(1,4,5)P3]. Moreover, L-ch-Ins(2,3,5)PS3 and D-6-deoxy-Ins(1,4,5)PS3 were able to inhibit the response to Ins(1,4,5)P3 with Ki values (6 microM and 33 microM, respectively) virtually identical to their EC50 values for Ca2+ release. This is consistent with partial agonist behavior, because these compounds exhibit low maximal responses when the extent of Ca2+ release is examined. These compounds represent the first examples of inositol-based analogues with low intrinsic activity and may point the way towards the design of selective antagonists at Ins(1,4,5)P3 receptors. It also seems probable that these may represent the first true affinity values of inositol phosphates at the active receptor.