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

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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.

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