Responses of human Col-24 epithelial layers after treatment with a) 100 nm 2A, 3A, 4A, or 5A. Desensitization of responses to 10 nm hPP after the indicated concentrations of 1A (b–d), or 2A (b), 3A (c), or 4A (d) in nM. The black bars show responses to hPP without prestimulation. The white bars in (c,d) reflect hPP responses after the addition of 100 nM unconjugated Pam or PEG5.