Formaldehyde and Cancer Pain Figure 5. Enhancement of low pH on formaldehyde- or capsaicin-induced TRPV1 currents in TRPV1-CHO cells in vitro and formaldehyde-induced C-fiber discharges in vivo. (A) Formaldehyde (FA)-induced currents and pH 6.0 enhancement on the currents with patch clamp recording. TRPV1 antagonist capsazapine (CPZ) inhibited both the formaldehyde-induced currents and the pH 6.0 enhancement. (B) Statistical results of low pH enhancement of formaldehyde-induced currents. (C) Formaldehyde enhancement on capsaicin (CAP)-induced currents. (D) Statistical results of formaldehyde enhancement on capsaicin-induced currents. n = 6,10. (E) Formaldehyde-induced C-fiber discharges under an acidic environment (pH 5.0) with extracellular recording in normal rats. The discharge was inhibited by CPZ. (F) Statistical results of CPZ inhibition on the formaldehyde-induced C-fiber discharges. * p,0.05, ** p,0.01. n = 3. doi:10.1371/journal.pone.0010234.g005 PLoS ONE | www.plosone.org 9 April 2010 | Volume 5 | Issue 4 | e10234