Intracellular Ca2+ stores of T lymphocytes: Changes induced by in vitro and in vivo activation

Emilio Clementi, Gianvito Martino, Luigi M E Grimaldi, Elena Bramhilla, Jacopo Meldolesi

Research output: Contribution to journalArticlepeer-review

Abstract

Intracellular Ca2+ stores were investigated in resting and activated splenic T lymphocytes from Lewis rats. Activation was obtained either in vitro (spleen cells isolated from "naive" rats exposed to concanavalin A for 24 h) or in vivo (spleen cells from rats with fully developed symptoms of experimental allergic encephalomyelitis). In both experimental conditions several changes of Ca2+ homeostasis were observed with respect to resting lymphocytes: (1) a threefold increase of the total intracellular calcium (from 1.15 to 3.5 mmol/1); (2) a moderate increase of the pool sensitive to inositol 1,4,5-trisphosphate (IP3), investigated both in intact T lymphocytes (fura-2 and 45Ca2+-release techniques in cells challenged with phytohemagglutinin) and in T lymphocytes permeabilized with β-escin (45Ca2+release induced by saturating concentrations of IP3); and (3) the appearance of a pool released by the endoplasmic reticulum (ER) Ca2+ ATPase inhibitor thapsigargin (Tg), but insensitive to IP3, which, therefore, appears to be localized in areas of the ER devoid of the cognate receptor. The latter two findings were paralleled in activated lymphocytes by an increase of expression of ER markers, involved (calreticulin; Ca2+ ATPase) or not (protein disulfide isomerase) in the regulation of Ca2+ homeostasis. In contrast, calnexin (another ER marker) and the receptor for IP3 were increased to only a moderate extent. Finally, an enlargement of non-ER Ca2+ pools was observed in the cells pretreated with Tg in which 45Ca2+ release was induced by the Ca2+ ionophore ionomycin. Our results document structural and functional changes of intracellular Ca2+ stores which might play an important regulatory role in activated T lymphocytes.

Original languageEnglish
Pages (from-to)1365-1371
Number of pages7
JournalEuropean Journal of Immunology
Volume24
Issue number6
Publication statusPublished - Jun 1994

Keywords

  • Ca stores
  • Experimental allergic encephalomyelitis
  • T lymphocyte activation

ASJC Scopus subject areas

  • Immunology

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