Effects of MET-1 on DRG neuron excitability is mediated in part by serine proteases. A, MET-1 decreased excitability of DRG neurons by increasing rheobase compared with media; this effect was abolished following addition of the PI mixture (1:10,000) (N = 9 mice). B, MET-1 decreased excitability of DRG neurons by increasing rheobase compared with media; this effect was abolished following addition of the serine PI FUT-175 (100 μm) (N = 10 mice). C, The effect of MET-1 on the decrease in excitability of DRG neurons was not abolished following addition of a cysteine PI (E64; 0.03 μm), aminopeptidase inhibitor (bestatin; 0.20 μm), acid PI (pepstatin; 0.03 μm), or metallo-PI (EDTA; 10 μm) (N = 3–5 mice/group). D, The serine protease, cathepsin G (1, 10, 50, and 100 nm) concentration-dependently recapitulated the effects of MET-1 on excitability of DRG neurons by increasing rheobase compared with media (N = 5 mice). *p < 0.05 (one-way ANOVA with Newman–Keuls post hoc test). **p < 0.01 (one-way ANOVA with Newman–Keuls post hoc test). #p < 0.05 compared with 50 nm (one-way ANOVA with Newman–Keuls post hoc test).