Different suppressive effect of lidocaine on persistent Na+ current and transient Na+ current in dorsal root ganglion neurons

Objective To investigate the different suppressive effect of lidocaine on persistent Na+ current and transient Na+ current in injured or uninjured dorsal root ganglion neurons. Methods Totally 23 SD rats were randomly divided into 2 groups; control group (n = 10) and chronically compressed DRG (dorsal root ganglion) group (CCD group, n = 13). Rats were anesthetized and DRG was isolated. Single DRG neuron was isolated by enzymatic disassociation method. Persistent Na+ current (INaP) and transient Na+ current (INaT) were elicited in voltage clamp mode. Results The presence of INaP was testified in most DRG neurons (38/46 neurons in CCD group and 31/39 neurons in control group, P>0.05). However, the current density of INaP in CCD group (4.6 ± 0.6 pA/pF, n = 38 neurons) was greater than that in control group (2.5 ± 0.4 pA/pF, n = 31 neurons) (P<0.05). The characteristics of INaP was observed and found that INaP could be blocked by 0.2 μmol/L tetrodotoxin easily. Furthermore, the does-effect relationship of Iidocaine on INaP and INaT were also examined. INaP and INaT were suppressed by different concentrations of lidocaine, the range for INaP was 5-20 μmol/L and for INaT was 0.05-2 mmol/L. Conclusion INaP and INaT were suppressed by different concentrations of lidocaine. INaP was suppressed by very low concentration of lidocaine (5-20 μmol/L). However, INaT could only be blocked by high concentration of lidocaine (0.05-2 mmol/L).