Gatekeeping Extracellular Calcium

Abstract

The inositol 1,4,5-trisphosphate receptor (IP 3 R) 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. found that a very small number of IP 3 Rs--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 IP 3 Rs had altered properties of the channel currents recorded at the cell surface and responded to externally applied channel regulator. Thus, the authors propose that IP 3 Rs allow the intracellular second messenger IP 3 to cause release of internally stored calcium both from the endoplasmic reticulum and 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 IP 3 R appears to be insensitive to depletion of internal stores. O. Dellis, S. G. Dedos, S. C. Tovey, T.-U.-Rahman, S. J. Dubel, C. W. Taylor, Ca 2+ entry through plasma membrane IP3 receptors. Science 313 , 229-233 (2006). [Abstract] [Full Text] D. L. Gill, M. A. Spassova, J. Soboloff, Calcium entry signals--Trickles and torrents. Science 313 , 183-184 (2006). [Summary] [Full Text]