Effects of 1,8-cineole on Na(+) currents of dissociated superior cervical ganglia neurons.

1,8-Cineole is a terpenoid present in many essential oil of plants with several pharmacological and biological effects, including antinociceptive, smooth muscle relaxant and ion channel activation. Also, 1,8-cineole blocked action potentials, reducing excitability of peripheral neurons. The objective of this work was to investigate effects of 1,8-cineole on Na(+) currents (INa(+)) in dissociated superior cervical ganglion neurons (SCG). Wistar rats of both sexes were used (10-12 weeks old, 200-300g). SCG's were dissected and neurons were enzymatically treated. To study 1,8-cineole effect on INa(+), the patch-clamp technique in whole-cell mode was employed. 1,8-Cineole (6.0mM) partially blocked INa(+) in SCG neurons. The effect stabilized within ∼150s and there was a partial recovery of INa(+) after washout. Current density was reduced from -105.8 to -83.7pA/pF, corresponding to a decrease to ∼20% of control. 1,8-Cineole also reduced the time-to-peak of INa(+) activation and the amplitude and decay time constants of INa(+) inactivation. Current-voltage plots revealed that 1,8-cineole left-shifted the V1/2 of both activation and inactivation curves by ∼10 and ∼20mV, respectively. In conclusion, we demonstrate that 1,8-cineole directly affects Na(+) channels of the SCG by modifying several gating parameters that are likely to be the major cause of excitability blockade.