Blockade of released PAI-1 from PC12 cells: effect on catecholamine secretion. PC12 cells were labeled with [³H]–norepinephrine, washed with release buffer, and incubated at 37°C for 45 minutes in release buffer with either rabbit anti–PAI-1 IgG (open bars) or normal rabbit IgG (solid bars) in the presence of 2 μM plasminogen. After incubation, the cells were treated with 60 μM nicotine (+) or buffer (−). Results are mean ± SEM; n = 3 for each group. Nicotine-mediated catecholamine secretion was significantly decreased from cells treated with anti–PAI-1 IgG compared with secretion from cells treated with nicotine plus normal rabbit IgG (P < .001).