Inositol-1,3,4,5-tetrakisphosphate induces calcium mobilization via the inositol-1,4,5-trisphosphate receptor in SH-SY5Y neuroblastoma cells
Wilcox, R.A.; Challiss, R.A.; Liu, C.; Potter, B.V.; Nahorski, S.R.
Molecular Pharmacology 44(4): 810-817
1993
ISSN/ISBN: 0026-895X PMID: 8232232 Document Number: 409709
myo-Inositol-1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P-4)-induced Ca-2+ mobilization was examined in saponin-permeabilized SH-SY5Y cells using myo-inositol hexakisphosphate-supplemented buffer to prevent Ins(1,3,4,5)P-4-3-phosphatase-catalyzed back-conversion of exogenous Ins(1,3,4,5)P-4 to myo-inositol-1,4,5-trisphosphate (Ins(1,4,5)P-3). The Ins(1,3,4,5)P-4 concentration-response curve for Ca-2+ release in SH-SY5Y cells exhibited an EC-50 of 2.5 mu-M, compared with 52 nM for Ins(1,4,5)P-3, with the maximally effective concentration of Ins(1,3,4,5)P-4 (100 mu-M) mobilizing the entire Ins(1,4,5)P-3-sensitive pool. Both Ins(1,3,4,5)P-4- and Ins(1,4,5)P-3-induced Ca-2+ mobilizations were heparin sensitive. Further, L-chiro-inositol-2,3,5-trisphosphorothioate, a recently identified low intrinsic activity Ins(1,4,5)P-3 receptor partial agonist, shifted both the Ins(1,4,5)P-3 and Ins(1,3,4,5)P-4 concentration-response curves significantly rightward, with similar potencies. However, binding studies demonstrate that L-chiroinositol-2,3,5-trisphosphorothioate interacts very poorly (IC-50 gt 30 mu-M) with specific Ins(1,3,4,5)P-4 binding sites that have been previously characterized in pig cerebellum. Carbachol-pretreated SH-SY5Y cells (1 mM, gtoreq 6 hr) exhibit a decrease in Ins(1,4,5)P-3 receptor number, accompanied by both a rightward shift and a reduced maximal Ca-2+ release in their Ins(1,4,5)P-3 concentration-response curve. Here both Ins(1,4,5)P-3 and Ins(1,3,4,5)P-4 concentration-response curves were found to exhibit identically reduced maximal Ca-2+ release responses and about 4-fold rightward shifts in EC-50 values. Together, these observations provide compelling evidence for our hypothesis that Ins(1,3,4,5)P-4 exhibits weak but full agonist status at Ins(1,4,5)P-3 receptor-operated Ca-2+ channels in SH-SY5Y cells.