Reverse fibrin zymography of catecholamine storage vesicle proteins. PC12 cells were incubated at 37°C for 30 minutes in release buffer in the presence (+) or absence (−) of the secretagogue, BaCl2 (2 mM). The releasates were electrophoresed on 10% SDS gels and subjected either to reverse fibrin zymography as described in “Reverse fibrin zymography” (A), or Western analysis using an IgG fraction of rabbit anti–rat PAI-1 (B).