ATP, UTP, and PPi reduce VSMC cell death but have no effect on osteoblast survival. (a) ATP and (b) UTP dose dependently decrease the proportion of dead cells in calcifying VSMC cultures by up to 75%; (c) ADP and (d) UDP have no effect. (e) PPi reduced the level of dead cells by up to 80%. (f–i) ATP, UTP, ADP and UDP do not influence osteoblast viability. (j) PPi at the highest dose tested caused a small increase in the percentage of dead cells. (k–m) Culture of VSMCs in calcifying conditions was associated by an increased level of apoptosis (up to 2.3 fold). ATP, UTP and PPi (≥10 μM) reduced the amount of apoptosis to levels seen in non-calcifying cells. Values are mean ± SEM (n = 6), *p < 0.05, **p < 0.01, ***p < 0.001