concanavalin-a and ethylisopropylamiloride

The effects of arachidonic acid (AA) and the lectin mitogens, concanavalin A (Con A) and phytohemagglutinin (PHA), on [Ca2+]i and pHi in rat thymocytes have been studied by using the intracellular fluorescent probes, Fura-2 and BCECF. It was revealed that exogenous AA (3 microM), in addition to the well-known changes in basal [Ca2+]i and pHi, also caused a complete blockade of [Ca2+]i and pHi signals induced by Con A (10 micrograms/ml) and PHA (10 micrograms/ml). In contrast, exposure of thymocytes to mitogens did not prevent the AA-induced increase in [Ca2+]i and decrease in pHi. In experiments with sodium propionate, the similarity between AA action and EIPA (ethylisopropylamiloride), an inhibitor of Na+/H+ exchangers, was revealed. It is proposed that the inhibitory effect of AA on mitogen-induced lymphocyte proliferation is due primarily to the blockade of transmembrane [Ca2+]i and pHi signals, associated with a sustained cytosolic acidification.

Topics: Amiloride; Animals; Arachidonic Acid; Calcium; Concanavalin A; Cytosol; Fluoresceins; Fluorescent Dyes; Fura-2; Hydrogen-Ion Concentration; Mitogens; Phytohemagglutinins; Rats; Rats, Wistar; Thymus Gland

The role of intracellular Ca2+ and H+ concentrations in radiation-induced interphase death of rat thymocytes has been studied. In response to concanavalin A treatment in the Ca(2+)-containing medium, or to the CaCl2 treatment in the Ca(2+)-free medium, the [Ca2+]i rise in irradiated cells was as in the non-treated cells. No changes in the level of [Ca2+]i and pHi were found within 1 h after irradiation of thymocytes with a dose of 6 Gy. 15 microM 5-(N-ethyl-N-isopropyl)-amiloride, an inhibitor of Na+/H+ exchange, did not affect the DNA fragmentation. The fragmentation was prevented by 2-4 microM (1-[bis(4-chlorophenyl)methyl]-3-[2-(2,4-dichlorophenyl)]-2-[(2,4- dichlorophenyl)-methoxy]-ethyl)-1-H-imidazolium chloride, an inhibitor of calmodulin. The above data indicate that triggering of interphase death in irradiated thymocytes is not mediated by changes in either [Ca2+]i or pHi. Such changes seem to be involved in intermediate steps of the interphase death process.

Topics: Amiloride; Animals; Antiporters; Biological Transport; Calcium; Calmodulin; Cell Death; Concanavalin A; DNA Damage; Hydrogen-Ion Concentration; Imidazoles; Male; Radiation Injuries, Experimental; Rats; Rats, Wistar; Thymus Gland; Time Factors

Topics: Amiloride; Animals; Arachidonic Acid; Benzimidazoles; Concanavalin A; Cytoplasm; Gossypol; Hydrogen-Ion Concentration; Kinetics; Lipoxygenase Inhibitors; Masoprocol; Oxidation-Reduction; Rats; Sodium-Hydrogen Exchangers; Thymus Gland