Kinetic properties of tetrodotoxin-sensitive and tetrodotoxin-resistant sodium channel currents in neonatal rat trigeminal ganglion neurons.

The kinetic properties of tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) Na' channels in acutely dissociated neonatal rat trigeminal ganglion neurons were studied using whole-cell and cell-attached patch-clamp recordings. The time course of TTX-R currents was slower than that of TTX-S currents. Compared with TTX-S currents, TTX-R currents had more positive half-activation and half-inactivation voltages. TTX-R currents recovered from inactivation much faster than TTX-S currents. Cell-attached patch recordings showed that the slope conductance of single TTX-S and TTX-R channels was 14.6 pS and 7.8 pS, respectively. TTX-R channels had longer open-times and more dispersed latent-times than TTX-S channels. The convolution of the first latency distribution with the open-time distribution revealed that the slower time course of TTX-R currents is due to longer open-times and more dispersed latent-times of the TTX-R channels compared with those of the TTX-S channels. These findings suggest that TTX-R Na+ channels in trigeminal ganglion neurons have similar kinetic property to brain TTX-S Na+ channels, but not to structurally homologous cardiac Na+ channels.