Immune responses in lymphocytes require cellular ccumulation of large amounts of calcium (Ca2+) from extracellular sources. In the T cell tumor line Jurkat, receptors for the Ca2+-releasing messenger inositol 1,4,5-trisphosphate (IP3) were localized to the plasma membrane (PM). Capping of the T cell receptor-CD3 complex, which is associated with signal transduction, was accompanied by capping of IP3 receptors. The IP3 receptor on T cells appears to be responsible for the entry of Ca2+ that initiates proliferative responses.
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