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Science 14 July 2006:
Vol. 313. no. 5784, p. 144
DOI: 10.1126/science.313.5784.144n
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The inositol 1,4,5-trisphosphate receptor (IP3R) allows regulated release of calcium from intracellular stores. These receptors have also been reported to exist in other compartments within the cell, but their roles have been uncertain. Dellis et al. (p. 229; see the Perspective by Gill et al.) found that a very small number of IP3Rs--only about two per cell--exist in the plasma membrane, where they appear to account for an appreciable fraction of calcium entry into B cells after stimulation of the B cell receptor. Cells expressing modified IP3Rs had altered properties of the channel currents recorded at the cell surface and responded to externally applied channel regulator. Thus, the authors propose that IP3Rs allow the intracellular second messenger IP3 to cause both release of internally stored calcium from the endoplasmic reticulum, but also from outside the cell, through the plasma membrane. Although store depletion is well known to cause calcium influx across the plasma membrane, the plasma membrane IP3R appears to be insensitive to depletion of internal stores.




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