Insulinotropic activity of soluble PA nanofibers. The positive control exendin-4, GLP-1-mimetic PA, control PA, and peptide control Ser[2]exendin(1–9) were assayed for stimulation of 4-hour insulin release from RINm5f cells in monolayer culture as quantified by ELISA (a,b; * p<0.05, ** p<0.01 vs. no treatment; # p<0.05, ## p<0.01 vs. Ser[2]exendin(1–9)). Glucose depletion fully abrogated activity of the GLP-1-mimetic PA but not exendin-4 (c; ** p<0.01 vs. 13.6mM glucose, # p<0.05 vs. 2.5mM glucose), while PKA inhibitor H-89 partially abrogated activity and lipid raft ablator β-MCD fully abrogated activity (d; * p<0.05, ** p<0.01 vs. H-89; # p<0.05, ## p<0.01 vs. no treatment). Error bars represent S.E.M.