Changes in intracellular calcium and in membrane currents evoked by injection of inositol trisphosphate into Xenopus oocytes.

Intracellular calcium was monitored by the use of aequorin in voltage-clamped oocytes of Xenopus laevis. Injection of inositol trisphosphate (IP3) into oocytes elicited slowly rising and decaying aequorin/calcium signals and produced oscillatory chloride membrane currents. These responses did not depend upon extracellular calcium, since they could be elicited in calcium-free solution and after addition of cobalt or lanthanum to block calcium channels in the surface membrane. We conclude that IP3 causes the release of calcium from intracellular stores in the oocyte. Injections of calcium gave aequorin and membrane current responses that were more transient than those seen with IP3.