Figure 7.

PIR in the LG neuron persists in the presence of TTX during either CabPK application or dynamic-clamp coinjection of artificial I_M plus I_Trans-LTS. A, Top, In the presence of TTX saline, a 5 s hyperpolarization in the LG neuron from a depolarized baseline was followed by a direct return to the depolarized baseline. Middle, During CabPK superfusion in TTX saline, a comparable 5 s hyperpolarization in LG was followed by PIR, albeit without action potentials. Here, the depolarized baseline resulted from the influence of CabPK. Bottom, CabPK superfusion in TTX saline containing 0.1× normal Ca²⁺, substituted with equimolar Mn²⁺, did not enable PIR after the same hyperpolarizing step as above. All recordings were from the same LG neuron. B, Top, Dynamic clamp injection of artificial I_MI (g_MI, 80 nS) plus I_Trans-LTS (g_Trans-LTS, 100 nS) in TTX saline enabled PIR in the LG neuron after a hyperpolarizing step. The initial dip in the LG neuron membrane potential occurred in all (n = 4) of these responses to hyperpolarizing current injection during the dynamic-clamp coinjections but not during the individual injections (e.g., see below). Middle, bottom, In contrast, separate dynamic-clamp injection of I_MI (middle) or I_Trans-LTS (bottom) in TTX saline did not enable PIR in the LG neuron. Note that, in the bottom recording without artificial I_MI, the LG neuron resting potential is not depolarized.