TRANSIENT ELEVATIONS OF CYTOSOLIC-FREE CALCIUM RETARD SUBSEQUENT APOPTOSIS IN NEUTROPHILS IN-VITRO

Elevation of cytosolic calcium ([Ca2+]i) has been reported to induce a poptosis in a number of cell types. However, in the neutrophil, which undergoes apoptosis constitutively during aging in vitro, activation b y inflammatory mediators elevates [Ca2+]i and prolongs lifespan via in hibition of apoptosis. To examine this paradox, we investigated the ef fects of modulation of [Ca2+]i upon apoptosis of neutrophils in vitro. Calcium ionophores (A23187, ionomycin) retarded apoptosis in neutroph il populations after 20 h (P < 0.001). Conversely, intracellular Ca2+- chelation, using bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPT A) acetoxymethyl ester (AM) promoted apoptosis (P < 0.02). W-7 (an inh ibitor of calmodulin) also promoted apoptosis (P < 0.05). Measurements of [Ca2+]i, using fura-2, showed (a) increased apoptosis in neutrophi l populations was not associated with elevated [Ca2+]i, (b) neutrophil s cultured with ionophore at concentrations inhibiting apoptosis exhib ited transient (< 1 h) elevations of [Ca2+]i, to levels previously rep orted with receptor-mediated stimuli, and (c) BAPTA was able to preven t the elevation of [Ca2+]i and the inhibition of apoptosis produced by ionophore. Modulation of apoptosis occurred without alterations in in tracellular pH. Thus, in the neutrophil, unlike lymphoid cells, elevat ion of [Ca2+]i exerts an inhibitory effect upon apoptosis. Furthermore , these data suggest that transient elevation of [Ca2+]i elicits signa ling events leading to prolonged inhibition of apoptosis.