Aristolochic acid, a plant extract used in the treatment of pain,is a regulator of K2P channels.

Currents through wild-type and mutated human K2P channels expressed in tsA201 cells were measured using whole-cell patch-clamp recordings in the presence and absence of AristA.Application of AristA resulted in an enhancement of current through TREK1 and TREK2 channels of 26 ± 6 % (mean ± SEM, n = 6) and 44 ± 11 % (n = 6), respectively. Enhancement of both currents was rapid and easily reversible. There was some voltage-dependence to the enhancement for both currents. By contrast, AristA (100 µM) had little effect on current through TRAAK channels with an enhancement of 8 ± 5 % (n = 5), or on the short form of TREK1 channels (TREK1_ΔN), with an enhancement of -4 ± 5 % (n = 5).

In contrast to the enhancement seen at high concentrations for TREK1 and TREK2 channels, we observed that AristA was aninhibitor of TRESK channelswith a calculated 50% effective concentration of 13 µM for AristA on TRESK (95% confidence intervals 11 – 18 μM) and a Hill slope of 0.56 (95% confidence intervals 0.43 – 0.65). As for enhancement of TREK channels, the effect of AristA was voltage-dependent. Altering the internal calcium buffer concentration had nosignificant effect on inhibition of TRESK by AristA (100 μM) with 73 ± 4 % (n = 6)inhibition in 0.1 mM EGTA and 79 ± 2 % (n = 6) inhibition in5 mM EGTA.Furthermore, inhibition of TRESK did not depend on the phosphorylation of key intracellular serine residues(3).S252A_S264A mutated TRESK channels had a significantly larger current density than WT TRESK channels (48 ± 3 pA/pF, n = 31 versus 27 ± 2 pA/pF, n = 28, p < 0.05, Student t-test), however, AristA (100 μM) still inhibited channel current by 80 ± 2% (n = 6). For S252E_S264E channels, current density was not significantly different to wild-type channels (33 ± 3 pA/pF, n = 39). AristA (100 μM) was, again, able to inhibit current through these channels by 73 ± 5 % (n = 5). On the other hand, mutations of bulky residuesin the M2 and M4 inner pore regions (F145A_F352A) completely abolished AristA inhibition of TRESK (0 ± 5 %, n = 7).

Enhancement of both TREK1 and TREK2 channel activity by AristAmay contribute to a therapeutically useful effect of this compound in pain and may help to explain the persistent use of plant extracts containing this compound in herbal remedies for pain (1). Hydroxy-α-sanshool, a primary active ingredient of Szechuan peppers, has been shown to block TRESK channels and this action has been proposed to underlie the distinctive numbing effect induced by this natural, widely-used analgesic(4).Since AristA is a potent inhibitor of TRESK channels, it might be predicted to act in a similar manner to hydroxy-α-sanshool to produce analgesia.

1. Scarborough J (2011). Pharmacy in History 53: 3–21.

2. Mathie A, Veale EL (2015). Pflugers Arch. 467: 931-943.

3. Czirják G, Enyedi P (2010). J Biol Chem. 285: 14549-14557.

4. Bautista DM et al. (2008). Nat Neurosci. 11: 772-779.