[Xylazine Produced Analgesic Effect via Inhibits Hyperpolarization-activated Cyclic Nucleotide-gated Ion Channels Currents].Sichuan Da Xue Xue Bao Yi Xue Ban. 2019 Jan; 50(1):20-26.SD
To investigate the analgesic mechanism of xylazine by inhibiting the activation of hyperpolarized cyclic nucleotide-gated (HCN) ion channels.
HCN subchannel 1 (HCN1) knockout mice (HCN1-/-) and HCN1 wild type mice (HCN1+/+) were intraperitoneally injected with physiological saline and xylazine (10, 20, 30, and 40 mg/kg). Mechanical pain test and tail flick test were used to test the analgesic effect of xylazine by using the percentage of the maximal possible effect (%MPE); The control group and test groups of different concentrations of xylazine (12.5, 25, 50, and 100 μmol/L) were set up using HEK 293 cells transfected HCN1 plasmid and HCN subchannel 2 (HCN2) plasmid, respectively. The activated current of hyperpolarized HEK 293 cells expressing HCN1 and HCN2 ion channels and the inhibition rate of xylazine on hyperpolarization-activated currents were recorded using a whole cell patch clamp.
The results demonstrated that %MPE of the mechanical pain stimuli test and the thermal radiation stimuli test increased with the higher concentration of xylazine injected for both HCN1+/+ mice and HCN1-/-mice. When injecting xylazine by 30 mg/kg and 40 mg/kg, the %MPE of mechanical pain stimuli test for HCN1-/- mice were %MPE= (62.06±14.72) % and %MPE= (69.92±16.09) %, respectively; and the percentages of tail flick tests were (52.50±1.97) % and %MPE= (64.74±6.34) %, respectively. But for HCN1+/+ mice, the percentages of mechanical pain stimuli test were %MPE= (75.47±8.06) % and %MPE= (86.35±11.31) %; respectively, and the percentage of tail flick tests were %MPE= (57.83±4.82) % and (74.98±9.35) %. The analgesic effect results of the mechanical pain test and tail flick test of HCN1+/+ mice were significantly different from HCN1-/- mice (P<0.05). Whole-cell patch clamp test results showed that xylazine had inhibitory effects on the currents of HCN1 and HCN2 ion channels, and the hyperpolarization-activated currents inhibition rate of HCN1 by xylazine (12.5-100 μmol/L) was between (24.62±23.62) %- (62.40±15.48) %; V1/2 of HCN1 was between (-79.58±1.56) mV- (-98.95±3.57) mV. The Ih inhibition rate of HCN2 by xylazine (12.5-100 μmol/L) was between (29.19±17.82) %- (80.02±6.64) %; with V1/2 of HCN2 between (-102.17±1.36) mV- (-117.48±2.38) mV.
Xylazine showed better analgesic effect on HCN1+/+ mice than HCN1-/- mice. Xylazine can produce analgesic effect by inhibiting HCN ion channel currents.