Reconstitution of a T cell receptor-stimulated plasma membrane calcium transporter: lack of dependence on inositol phosphates

Abstract

The activation of T lymphocytes, like many cells, requires a rapid rise in intracellular Ca 2+ secondary to both an influx and a release from intracellular stores. The latter is activated by inositol-1,4,5-trisphosphate [Ins(1,4,5)P 3]. It is controversial if inositol phosphates can also stimulate a plasma membrane Ca 2+ channel in T cells. We have studied the human T cell line HPB-ALL which, upon stimulation of its antigen receptor, does not generate detectable levels of Ins(1,4,5)P 3 or internal Ca 2+ release, but does have a Ca 2+ influx. We have reconstituted a receptor-activated Ca 2+ transporter from plasma membranes from these cells which has properties similar to the transporter observed in vivo and does not require inositol phosphates for activation. These data show that mitogens may activate more than one type of ligand-gated Ca 2+ transport mechanism in T lymphocytes.