Myo‐inositol 1,3,4,5‐tetrakisphosphate can independently mobilise intracellular calcium, via the inositol 1,4,5‐trisphosphate receptor: studies with myo‐inositol 1,4,5‐trisphosphate‐3‐phosphorothioate and myo‐inositol hexakisphosphate

Abstract

Myo-inositol 1,3,4,5_tetrakisphosphate [Ins(1,3,4,5)P,] acts as a full agonist for Ca" release in saponin-permeabilised SH-SYSY neuroblastoma cells. Studies were conducted in the presence of myo-inositol hexakisphosphate (InsP,, 10 BUM), to inhibit the Ins( 1,3,4,5)P,-3-phosphatase catalysed back conversion of Ins(l,3,4,5)P, to Ins(lfl,S)P,. HPLC anaiysis confirmed that Ins(l,3,4,5)P, releases the entire content of Ins(l,4,5)P,-sensitive intra~Ilular Ca2* stores, independent of 3-phosphate activity. Further we utilised racemic myo-inositoll,4,5-t~sphosphat~3-phosphorothioate [m-Ins(l,3,4,5)P,-3S], a novel intrinsically Ins(l,3,4,5)P~-3-phosphatase resistant Ins(l,3,4,5)P, analogue. DL-Ins(1 ,3,4,5)P,-3S specifically displaced ['H]Ins(l,4,5)P, from bovine adrenal cortex Ins(1,4,5)P, binding sites (IC,, = 889 nM, compared to Ins(1,4,5)P,, ICs, = 4.4 nM and Ins(1,3,4,5)P,, I&, = 152 nM). m.-Ins(l,3,4,5)P,-3S was a full agonist for Ca2' release (EC% = 4.7 PM), being 90-and 2-fold less potent than Ins(1,4,5)P, and Ins(l,3,4,5)P, (with InsP,), respectively. DL-Ins( 1,3,4,5)P.,-3S will be an important tool for identification of potentially exclusive Ins(l,3,4,5)P., second messenger functions, since its resistance to 3-phosphatase action precludes the inconvenient artefact of steady state Ins(1,4,5)P, generation.

Pharmacology of signaling induced by dopamine D1-like receptor activation

“…Essential components of these interconnected cascades are illustrated in Figure 2. Inositol 1,3,4,5-tetrakisphosphate which is formed by the further phosphorylation of IP 3 regulates the metabolism of IP 3 and works reciprocally with IP 3 to restore cytosolic calcium back into intracellular storage sites (Joseph et al, 1987; Hill et al, 1988; Wilcox et al, 1993; Loomis-Husselbee et al, 1996). Inositol 1,2,3,4,5,6-hexakisphosphate, similarly formed from sequential phosphorylation of IP 3 , is also involved in calcium homeostasis and other actions through which it modulates cell differentiation (Shamsuddin, 1999).…”

Stable overexpression of the type-1 inositol 1,4,5-trisphosphate receptor in L fibroblasts: subcellular distribution and functional consequences

“…Medium was changed daily, and confluent flasks were harvested using sterile PBS\EDTA, pelleted at 500 g max for 5 min, then reseeded at a density of 2i10% cells\cm#. SH-SY5Y human neuroblastoma cells were grown as described previously [25]. PC-12 rat adrenal pheochromocytoma cells were cultured in DMEM containing 5 % fetal calf serum, 10 % horse serum and the antibiotics listed above.…”

Inositol 1,3,4,5‐tetrakisphosphate enhances long‐term potentiation by regulating Ca2+ entry in rat hippocampus

“…Many studies indicate that Ins P 4 activates Ca 2+ release primarily from Ins P 3 ‐dependent internal stores alone, or facilitates responses via Ins P 3 (Gawler et al 1990; Parker & Ivorra, 1991; Wilcox et al 1993; Mills et al 1997). Therefore, we investigated how the inhibition of the ER‐dependent Ca 2+ release might modify the facilitatory Ins P 4 effect on LTP.…”

“…Many effects of Ins P 4 were characterized in several cell preparations derived, mainly, from cells other than from the central nervous system of mammals (Irvine, 1991). It seems that Ins P 4 acts either on different cell membrane conductances (Morris et al 1987; Sawada et al 1990; Wu et al 1991; Fadool & Ache, 1994) or activates Ca 2+ release primarily from Ins P 3 ‐dependent internal stores alone, or facilitates responses to Ins P 3 (Gawler et al 1990; Parker & Ivorra, 1991; Wilcox et al 1993; Mills et al 1997). In the central nervous system, Ins P 4 was shown to modulate VGCC conductances (De Waard et al 1992; Tsubokawa et al 1996).…”