Figure 3. Effect of pulsating fluid flow on TNF--induced apoptosis in periosteal fibroblasts, osteoblasts, and osteocytes. Apoptosis was induced by TNF- at 10 ng/mL for 16 hrs. (A) Apoptosis in the absence of L-NAME. One hour of PFF reduced caspase-3/7 activity in TNF--treated osteocytes by 25%, but not in osteoblasts and periosteal fibroblasts. Values obtained from 6 osteoblast, 7 periosteal fibroblast, and 8 osteocyte experiments are expressed as mean ± SEM of PFF-treated-over-control ratios (± PFF). (B) Apoptosis in the presence of L-NAME. Addition of 1 mM L-NAME to the culture medium during exposure to PFF blocked the inhibitory effect of PFF on caspase-3/7 activity in TNF--treated osteocytes, but did not affect apoptosis in osteoblasts and periosteal fibroblasts. Values, obtained from 3 experiments, are expressed as mean ± SEM of PFF-treated-over-control ratios (± PFF). Dashed line, ± PFF = 1 (no effect). PFF, pulsating fluid flow; PF, periosteal fibroblasts; OB, osteoblasts; OCY, osteocytes; L-NAME, N^G-Nitro-L-Arginine Methyl Ester. *Significant effect of PFF, p < 0.05.