Objective: To study the joint neurotoxic effects of phoxim (Pho) and fenvalerate (Fen) on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) Na(+) currents in dorsal root ganglion (DRG) neurons of adult rat.
Methods: Whole cell patch clamp technique was used to test the effects of Pho and Fen on TTX-S and TTX-R sodium currents in DRG neurons.
Results: The inactivation of TTX-R sodium channel was obviously slowed down by Fen. The tau(Na) of peak currents at doses of 10, 50 and 100 micromol/L Fen and control groups were (8.10 +/- 2.41) ms, (11.78 +/- 2.76) ms, P < 0.01, (8.76 +/-1.94) ms, P < 0.05 and (6.41 +/- 1.32) ms respectively. The inactivation of TTX-R sodium channel tail currents was also significantly delayed by Fen. The tau(Na) of the tail currents at doses of 10, 50, 100 micromol/L Fen and control groups were 6.11 +/- 0.52 (P < 0.05), 7.82 +/- 0.82 (P < 0.05), 7.23 +/- 1.09 (P < 0.05) and (4.91 +/- 0.97) ms separately. As compared with TTX-R sodium channel, the TTX-S sodium channel was less responsive to Fen exposure, which only led to slowly decay TTX-S sodium tail currents. There was no any effect of Pho on the TTX-S and TTX-R sodium channels. The mixed treatment of a Pho and Fen did not show joint effect on the sodium currents.
Conclusion: Both the peak and tail currents are changed by Fen, however, Fen has more remarkable effects on TTX-R than on TTX-S sodium channel. The combined exposure to Pho and Fen shows no joint effect on the sodium channel.