Fig. 4.

Firing-induced V_m hyperpolarization requires a transmembrane K⁺ gradient and voltage-gated Na⁺ channels. A: example CM cell (n = 3/3) with Na⁺ channel blockade (500 nM TTX). A broad range of depolarizing current injections failed to induce V_m hyperpolarization. B: example CM cell (n = 3/3) challenged with the firing protocol while extracellular [K⁺] was increased (12 mM) to shift K⁺ reversal potential near resting V_m. A tonic current was injected (−60 pA) to maintain V_m near resting values (−65 mV). C: example CM cell (n = 16/16) where a tonic hyperpolarizing current was injected to lower V_m ∼ −85 mV prior to and during the firing protocol. D: example MDc neuron with physiological temperatures (T = 35°C) Insets: traces, early and late in firing protocol. In all traces, a line marks the baseline resting V_m prior to and during stimulation.