Stimulus‐Induced Accumulation of Inositol Tetrakis‐, Pentakis‐, and Hexakisphosphates in N1E‐115 Neuroblastoma Cells

Abstract: When [³H]inositol‐prelabelled N1E‐115 cells were stimulated with carbamylcholine (CCh) (100 μM), high K⁺ (60 mM), and prostaglandin E, (PGE,) (10 μM), a transient increase in [³H]inositol pentakisphosphate (InsP₅) accumulation was observed. The accumulation reached its maximum level at 15 s and had declined to the basal level at 2 min. CCh, high K⁺, and PGE, also caused accumulations of [³H]inositol 1,4,5‐trisphosphate [Ins(1,4,5)P₃], [³H]inositol 1,3,4,6‐tetrakisphosphate [Ins(1,3,4,6)P₄], and 1³H]inositol hexakisphosphate (InsP₆). Muscarine and CCh induced accumulations of [³H]Ins(1,4,5)P₃, [³H]‐Ins(1,3,4,6)P₄, [³H]InsP₅, and [³H]InsP₆ with a similar potency and exerted these maximal effects at 100 μM, whereas nicotine failed to do so at 1 mM. With a slower time course, CCh, high K⁺, and PGE₁ caused accumulations of [³H]‐inositol 1,3,4‐trisphosphate [Ins(1,3,4)P₃] and [³H]inositol 1,3,4,5‐tetrakisphosphate [Ins(1,3,4,5)P₄]. In an N1E‐115 cell homogenate, [³H]Ins(1,4,5)P₃, [³H]Ins(1,3,4,5)P₄, and [³H]Ins(1,3,4)P₃ were converted to [³H]InsP₅ through [³H]‐Ins(1,3,4,6)P₄. The above results indicate that Ins(1,3,4,6)P₄, InsP₅, and InsP₆ are rapidly formed by several kinds of stimulants in N1E‐115 cells.