IP3 receptor-operated calcium entry.

This Perspective by Mikoshiba and Hattori is the third in a series on cellular calcium release mechanisms. The authors describe the regulated release of calcium from intracellular stores by the inositol 1,4,5 trisphosphate receptor (IP(3)R) and the relationship of this release mechanism to calcium influx from the extracellular milieu through store-operated calcium channels. They discuss a model proposing that intracellular and plasma membrane calcium channels are functionally and physically coupled.