Transmembrane signalling by the T cell antigen receptor. Perturbation of the T3-antigen receptor complex generates inositol phosphates and releases calcium ions from intracellular stores.

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Abstract
Antibodies against the T3-antigen receptor complex can activate the human T cell line, Jurkat, to produce interleukin 2. This activation is initiated by a receptor-mediated increase in the concentration of free cytoplasmic [Ca2+]i. In this communication, the mechanism by which the receptor complex increases [Ca2+]i in Jurkat cells was investigated. The initial receptor-mediated change in [Ca2+]i can occur when extracellular Ca2+ is depleted by EGTA [ethylene glycol bis(aminoethyl ether)-N,N,N'',N''-tetraacetic acid]. Perturbation of the T cell antigen receptor, therefore, generates a signal which mobilizes Ca2+ from intracellular stores. As inositol trisphosphate appears to function as such a signal for certain hormone receptors, the levels of inositol trisphosphate and of the other inositol phosphate compounds were measured in Jurkat. Antibodies to either the antigen receptor heterodimer or T3 determinants result in marked elevations of all 3 inositol phosphates. These changes in inositol phosphates are not secondary to the receptor-mediated increases in [Ca2+]i as demonstrated by the inability of the Ca2+ ionophore, ionomycin, to affect the levels of any of these compounds. In concentrations between 0.1 and 1 .mu.M, purified inositol trisphosphate releases Ca2+ from permeabilized Jurkat cells. During activation, perturbation of the T3-antigen receptor complex generates inositol trisphosphate. This compound functions as an intracellular signal to release Ca2+ from intracellular stores, leading to increases in [Ca2+]i.