Figure 7. LA inhibits TRPV1 by an extracellular site of action.

(A,B) Representative current traces from inside-out patches of WT-hTRPV1 (A) and I680A-hTRPV1 (B) challenged with capsaicin (500 nM) alone or in combination with 10 mM LA or pH 5.4. While 10 mM LA fails to inhibit both WT- and I680A-hTRPV1 in this mode, pH 5.4 induces as rapid and reversible inhibition. (C,D) Representative current traces from cell-attached recordings of WT-hTRPV1 (C) and I680A-hTRPV1 (D) challenged with capsaicin (500 nM) alone or in combination with 10 mM LA or pH 5.4. While 10 mM LA fails to inhibit both WT- and I680A-hTRPV1 in this mode, pH 5.4 induces as rapid and reversible inhibition due to intracellular acidosis. (E,F) Representative current traces from whole cell (E) and outside-out (F) WT-TRPV1 currents of the same cell, challenged with 50 nM capsaicin ±10 mM lactate at −60 mV. In both cases, we can see a clear inhibition of capsaicin-induced currents by lactate. (G) Single channel recordings in outside-out configuration at −30 mV (upper trace) reveal an increased open probability of TRPV1 channels upon capsaicin application (a) which is shifted back to the closed state by lactate (b). Sections a,b represent 300 ms of the upper trace with an expanded time scale (a, black, 200 nM CAP; b, red, 200 nM CAP+10 mM LA). The amplitude histogram (left bottom) displays a lactate inhibition of capsaicin-induced events leading to an increase in the closed state of TRPV1 channels.