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

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 $\mu m$ 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.