title: Agents that raise cAMP in human T lymphocytes release an intracellular pool of calcium in the absence of inositol phosphate production.
abstract: Prostaglandins (PGs) of the E series are recognized by specific receptors on T lymphocytes which lead to an increase in cAMP. The role of cAMP in modulation of T lymphocyte function is unknown. Here, we demonstrate that agents which increase cAMP in human T cells raise the intracellular free calcium concentration ([Ca2+]i). This increase in [Ca2+]i occurred following receptor stimulation with PGEs or by bypassing the receptor with the cell-permeant analog 8-(4-chlorophenylthio)-cAMP or forskolin, a direct activator of adenylyl cyclase. The calcium response to a submaximally stimulatory concentration of PGE2 was potentiated by the cAMP phosphodiesterase inhibitor isobutylmethylxanthine. A time course of cAMP production in response to PGE2 stimulation closely resembled the calcium response and suggested that the two events were coincident. The PGE2 concentrations required to achieve 50% maximum effect of cAMP production and increases in [Ca2+]i were similar, 0.07 and 0.15 microM respectively. Chelation of extracellular Ca2+ did not abolish the PGE2-stimulated Ca2+ response, suggesting that an intracellular source of calcium was sensitive to cAMP. Significant inositol phosphate production was not detected in response to PGE2 over a wide concentration range. The PGE2-induced calcium response curves were of lesser magnitude with shorter times to peak than those of a known inositol 1,4,5 trisphosphate-producing agonist, anti-CD3, suggesting distinct Ca2+ release mechanisms. However, the cAMP-releasable store appeared to be contained within the inositol trisphosphate-releasable store since no response could be seen with cAMP-elevating agents following emptying of the inositol trisphosphate-sensitive pool of Ca2+.
authors.affiliation: Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
authors.forename: L L
authors.initials: LL
authors.lastname: Kelley
authors.forename: P F
authors.initials: PF
authors.lastname: Blackmore
authors.forename: S E
authors.initials: SE
authors.lastname: Graber
authors.forename: S J
authors.initials: SJ
authors.lastname: Stewart
mesh_terms: D015703:Antigens, CD / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology; D017252:CD3 Complex; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D015232:Dinoprostone / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D007295:Inositol Phosphates; D011948:Receptors, Antigen, T-Cell; D005576:Colforsin; D004533:Egtazic Acid; D000242:Cyclic AMP; D015232:Dinoprostone; D002118:Calcium