Changes in the expression of large-conductance calcium-activated potassium channels in dorsal root ganglion neurons after electrical injury in rats′ sciatic nerves and its influence on sensory conduction function

Objective To study the changes in the expression of large-conductance calcium-activated potassium (BK_Ca) channels in dorsal root ganglion (DRG) neurons after electrical injury in rats′ sciatic nerves and its influence on sensory conduction function. Methods One-hundred and thirty-six adult SD rats were divided into normal control group, sham electrical injury group, and 75, 100, 125 V electrical injury groups according to the random number table, with 8 rats in normal control group and 32 rats in each of the rest 4 groups. Rats in normal control group were routinely fed without any treatment. Blunt dissection of the sciatic nerves of left hind leg of rats was performed in sham electrical injury group, while sciatic nerves of left hind leg of rats in electrical injury groups were electrically injured with corresponding voltage. Eight rats of normal control group fed for one week, and 8 rats from each of the rest four groups on post injury day (PID) 3 and in post injury week (PIW) 1, 2, 3 respectively were collected to detect the paw withdrawal mechanical threshold (PWMT). In addition, rats of 100 V electrical injury group in PIW 1 were collected and intrathecally injected with NS1619 after former PWMT detection, and PWMT was detected per 30 minutes within three hours post injection. The rats in each group at each time point were sacrificed after PWMT detection. The DRG of L₄ to L₆ segments of spinal cord was sampled to observe the BK_Ca channels distribution with immunohistochemical staining and to detect the protein and mRNA expressions of BK_Ca channels with Western blotting and reverse transcription-polymerase chain reaction respectively. Data were processed with one-way analysis of variance, analysis of variance of factorial design, and SNK test. Results (1) The PWMT values of rats in 75 and 100 V electrical injury groups on PID 3 and in PIW 1, 2, 3 were (5.8±0.6), (5.0±0.8), (4.2±0.3), (5.9±1.1) g; (5.3±1.3), (5.9±2.0), (4.5±2.7), (4.3±1.3) g, respectively, which were significantly lower than the value (s) in normal control group [(11.2±2.0) g] and sham electrical injury group [respectively (11.3±2.1), (12.0±2.0), (11.1±1.6), (10.3±2.1) g, with P values below 0.05]. The PWMT values of rats in 125 V electrical injury group decreased obviously on PID 3 and in PIW 1 [(6.1±1.6) and (5.7±1.7) g] as compared with the value (s) in normal control group and sham electrical injury group, and they were obviously increased in PIW 2 and 3 [(26.7±3.3) and (21.7±3.4) g] as compared with the value (s) of the rest 4 groups (with P values below 0.05). The PWMT of 100 V electrical injury group in PIW 1 firstly increased and then decreased within three hours post injection, which increased significantly at post injection minutes 30, 60, 90, 120 as compared with that before intervention [respectively (8.5±0.8), (9.7±1.2), (11.0±1.5), (8.6±0.8) g, with P values below 0.05]. (2) The positive expression of BK_Ca channels in large amount was observed in the cytoplasm and cytomembrane of neurons on the DRG of rats in normal control group and sham electrical injury group at each time point. The positive expression of BK_Ca channels in the cytoplasm and cytomembrane of neurons on the DRG of rats decreased over time in electrical injury groups, which was most obvious in 125 V electrical injury group. (3) There were no statistically significant differences in the protein expression of BK_Ca channels in DRG of rats among the five groups on PID 3 (with P values above 0.05). Compared with those in normal control group (0.477±0.027, 0.521±0.034, 0.475±0.022) and sham electrical injury group (0.511±0.025, 0.489±0.025, 0.483±0.032) in PIW 1, 2, 3, the protein expressions of BK_Ca channels in DRG of rats in 75, 100, 125 V electrical injury groups were decreased significantly (0.274±0.026, 0.202±0.019, 0.285±0.033; 0.253±0.022, 0.233±0.024, 0.203±0.017; 0.092±0.017, 0.095±0.021, 0.087±0.016, with P values below 0.05). The protein expressions of BK_Ca channels in DRG of rats in 125 V electrical injury group in PIW 1, 2, 3 were obviously lower than those in 75 and 100 V electrical injury groups (with P values below 0.05). (4) The mRNA expression levels of BK_Ca channels in DRG of rats in 75, 100, 125 V electrical injury groups on PID 3 and in PIW 1, 2, 3 were 0.326±0.021, 0.238±0.019, 0.291±0.022, 0.364±0.018; 0.264±0.020, 0.293±0.017, 0.243±0.023, 0.295±0.021; 0.134±0.023, 0.089±0.017, 0.074±0.018, 0.087±0.020, respectively, significantly decreased as compared with the level (s) in normal control group (0.581±0.051) and sham electrical injury group (0.603±0.045, 0.586±0.032, 0.614±0.045, 0.572±0.038), with P values below 0.05. The mRNA expression levels of BK_Ca channels in DRG of rats in 125 V electrical injury group at each time point were lower than those in 75 and 100 V electrical injury groups (with P values below 0.05). Conclusions The electrical injury in sciatic nerves results in reduction of the BK_Ca channels expression in rat′s DRG of corresponding spinal segments, which plays a role in the pathological process of sensory conduction dysfunction.