Expression of inositol 1,4,5-trisphosphate receptors changes the Ca2+ signal of Xenopus oocytes.

The receptors for the second messenger inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] form a family of closely related proteins that play an important role in regulating the free intracellular Ca2+ concentration. To test the hypothesis that changing the expression level of Ins(1,4,5)P3 receptors could alter the Ins(1,4,5)P3-mediated Ca2+ signal, we overexpressed Ins(1,4,5)P3 receptor type 1 (InsP3R-1) or type 3 (InsP3R-3) in Xenopus laevis oocytes. Expression of InsP3R-1 increased the velocity of the propagating waves of intracellular Ca2+ release but did not affect the Ins(1,4,5)P3-induced entry of extracellular Ca2+ across the plasma membrane. In contrast, expression of intracellular Ca2+ but markedly increased the magnitude and duration of Ca2+ influx. Immunolocalization studied revealed InsP3R-3 at the endoplasmic reticulum, with a relatively stronger signal at or near the plasma membrane. The results suggest that changing the expression level of an InsP3R can alter the Ins(1,4,5)P3-mediated Ca2+ signal and that InsP3R-1 and InsP3R-3 may have different biological functions.