抄録
DRG neurons express 7 voltage-gated Na+ channel α-subunits, 5 of which being sensitive to tetrodotoxin (TTX) and the remaining 2 being resistant. These channels show preferential distribution within DRG depending on the type of neurons, mediating Na+ currents (INas) with distinct kinetics. The preferential distribution of voltage-gated Na+ channels may bring about differential mechanisms of action potential generation. However, it is not known how each type of Na+ channels contributes to the generation of action potentials. Therefore, we investigated the correlation between INas in voltage-clamp recordings and corresponding action potentials in current-clamp recordings to clarify action potential electrogenesis in DRG neurons. We classified INas recorded in DRG neurons into four types on the basis of TTX sensitivity and kinetic properties. The action potentials in small DRG neurons were dependent on TTX-R/slow INa mediated by NaV1.8, whereas action potentials in large DRG neurons were mediated by TTX-S/fast INa. TTX-S/fast INa was switched off in small DRG neurons due to a hyperpolarizing shift of the steady-state inactivation. We also found that TTX-R/persistent INa mediated by NaV1.9 and TTX-S/persistent INa regulate subthreshold excitability in small and large DRG neurons, respectively. Thus, our results demonstrate that the action potentials in DRG neurons are generated and regulated with distinct mechanisms that may give rise to differential functional properties of DRG neurons. [Jpn J Physiol 55 Suppl:S129 (2005)]
