Inositol 1, 4, 5-Trisphosphate Induced Calcium Release from Corn Coleoptile Microsomes

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The effect of inositol 1, 4, 5-trisphosphate (IP₃) on Ca²⁺ release from microsomes of corn coleoptiles was investigated. Addition of micromolar concentrations of IP₃ to Ca²⁺ loaded microsomes resulted in rapid release of 20-30% of sequestered Ca²⁺. Maximal and half maximal Ca²⁺ release occurred at 20 and 8μM of IP₃ respectively. Part of the Ca²⁺ released by IP₃ was reaccumulated into microsomes within 4min. The amount of Ca²⁺ released by IP₃ was found to be dependent on free Ca²⁺ concentration in the incubation medium at the time of release. Maximum Ca²⁺ release was observed around 0.1 μM free Ca²⁺ concentration in the assay medium. These data suggest that IP₃ might act as a second messenger in plants in a manner similar to animal systems by altering cytosolic levels of calcium.