Apoptosis Induced by Adenosine 5’-triphosphate in Mouse Leukemic Cells. Nan Young Joo， Kyu Sang Park， Hae Sook Chung， In Deok Kong， and Joong Woo Lee Department of Physio1ogy， Yonsei University W onju College of Medicine， W onju 220 - 701， Korea Extracell띠ar ATP elicits various biological responses and plays a significant role in physiological regulation. Recent1y， ATP-induced growth inhibitions were reported in some tumor cell lines， but these effects and mechanisms are not well known. This study was conducted to investigate ATP-induced growth inhibition in mouse leukemic( P388DJ) cells. ATP inhibited cell growth in a dose-dependent manner as analyzed by MTS assay(IC5o: 33.1 μM). Nuc1eotides other than ATP， such as ADP(37.5 μM) and AMP(33.2 μM) had the same effects as ATP， but adenosine(57.8 μM) showed less effect than ATP. ATP attenuated the cells in Go/GJ and G2/M phases， but increased those in S phase in flow cytometric analysis. Hypodiploid cells(Ao)， the presumptive findings of apoptosis， were found among the ATP-treated cells. ATP induced DNA fragmentation into 180-200 bps as measured by electrophoresis. Some apoptotic cells were stained by TUNEL method. ATP increased the intracellular ++ ... ， .... .--++ free Ca" concentration([Ca]i) and the increment of [Ca]i was caused by influx from the extracellu1ar space. These results suggest that extracellular ATP induces growth inhibition through apoptosis.