EFFECTS OF CA2-MEMBRANE POTENTIAL AND CELL VIABILITY IN NUCLEATED CELLS FOLLOWING LYRIC COMPLEMENT ATTACK( DEREGULATION ON MITOCHONDRIAL)

We have previously shown [Papadimitriou JC. Ramm LE. Drachenberg CB. T rump BF. Shin ML. (1991) J. Immunol., 147, 212-217] that formation of lytic C5b-9 channels on Ehrlich ascites tumor cells induced rapid depl etion of adenine nucleotides associated with prelytic leakage precedin g cell death. Extracellular Ca2+ concentration ([Ca2+](e)) reduction b y chelation markedly delayed the onset of cell death, although the ade nine nucleotide leakage was enhanced. In the present study, we examine d the temporal relationships between ionized cytosolic Ca2+ ([Ca2+](i) ), mitochondrial membrane potential (Delta Psi(m)) and cell death in i ndividual cells by digital imaging fluorescence microscopy (DIFM), dur ing the earliest phase of C5b-9 attack. The results showed an immediat e, > 20-fold rise in [Ca2+](i), rapidly followed by dissipation of Del ta Psi(m) and subsequent acute cell death. These events were markedly delayed by chelation of Ca-e(2+), but not by nominally Ca2+ free mediu m. Differing from previous reports indicating propidium iodide labelin g of viable cells bearing C5b-9 channels, with DIFM we observed nuclea r fluorescence with that marker only in association with cell death. T hese findings indicate that Ca2+ influx through lytic C5b-9 channels i s responsible for the massive increase in [Ca2+](i), as well as for th e rapid loss of Delta Psi(m), followed by acute cell death. When this [Ca2+](i) increase is prevented, the cell death is probably related to metabolic depletion.