Inositol 1, 4, 5-trisphosphate-induced calcium mobilization is localized in Xenopus oocytes

Abstract

Injection of inositol 1, 4, 5-trisphosphate (Ins(1, 4, 5) P 3 ) into the animal pole of Xenopus oocytes induced membrane depolarization due to the internal mobilization of calcium, which activates a chloride conductance. Repetitive injections of Ins(1, 4, 5) P 3 results in desensitization probably as a result of depletion of the internal store of calcium. Desensitization was restricted to the region surrounding the site of injection. Injection of Ins(1, 4, 5) P 3 at one position induced desensitization, which failed to spread to a neighbouring region ( ca . 200 μm away). Even when sufficient Ins(1, 4, 5) P 3 was injected to induce calcium oscillations, there was still no evidence for the effects of Ins(1, 4, 5) P 3 spreading to neighbouring regions. The fact that periodic calcium transients could also be established by the repetitive injection of small amounts of Ins(1, 4, 5) P 3 suggests that calcium oscillations may also be localized. It is concluded that the Ins(1, 4, 5) P 3 -sensitive store of calcium comprises separate local compartments that can be activated independently of each other.