CHANGES IN INTRACELLULAR CALCIUM-CONCENTRATION AND PH OF TARGET-CELLSDURING THE CYTOTOXIC PROCESS - A QUANTITATIVE STUDY AT THE SINGLE-CELL LEVEL

This study reports on the changes in intracellular calcium concentrati on ([Ca2+](in) and intracellular pH ([pH](in)) that occur in K562 targ et cells during interaction with human Natural Killer (NK) cells. The data were obtained using a quantitative fluorescence microscope and fl uorescent ratio probes specific for [Ca2+](in) (Fura-2-AM) and [pH](in ) (BCECFAM). Results demonstrate that two types of target cell respons e to the attack by an NK cell can be distinguished. The target cell ei ther dies immediately, due to the complete breakdown of the membrane i mpermeability, or the initial membrane damage (i.e., increased membran e permeability) is repaired and the cell ''escapes'' immediate death. During both responses an increase of [Ca2+](in), takes pla(in) takes p lace in the target cells. In the cells that die immediately, however, [Ca2+](in) reaches higher levels (approximately 1,400 nM) than in the cells that restore the initial damage (approximately 700 nM). Changes in target cell [pH](in) are also detected during both responses. The d irection of the change (acidification or alkalinization) as well as th e level of the change depend on extracellular pH ([pH](ex) Also, [pH]( in) remains changed during the time the cells were followed (10 min), The programming time (i.e., the time from the initiation of the cytoto xic process to the time that a change in the physiological parameter w as detected) of the killing process that leads to an immediate target cell death appears to be shortest at [pH](ex) 7.3-7.6 (approximately 3 min). (C) 1995 Wiley-Liss, Inc.