This clearly shows that after nitrergic activation, Kv3 channels were no longer involved in AP repolarization. Additional contributions of nitrergic signaling by suppression of voltage-gated sodium currents have been reported in the MNTB (Steinert et al., 2008). The maximal rate of rise of APs in CA3 pyramidal neurons was unaltered following activation of nitrergic signaling (NO and PC; data not shown). Our data suggest the idea that AP repolarization could be mediated by different Kv families under different activity conditions in the same neuron. To test this hypothesis, we focused on the MNTB neuron, which has a well-documented expression

of Kv3.1b and Kv2.2 subunits. The restricted expression of Kv2.2 to the brain stem (Johnston et al., 2008) also allows use of a transgenic knockout Cisplatin mw (KO) with relatively few complications, which would not be possible

for a Kv2.1 KO because of its broader expression (Misonou et al., http://www.selleckchem.com/products/byl719.html 2005). The compact size of MNTB neurons with few dendrites also assisted voltage-clamp interpretation by minimizing space-clamp issues. Under control in vitro conditions, MNTB neurons possess around 23 nA of outward K+ current (at +50 mV), of which TEA-sensitive Kv3 currents account for 31% (Figure 6B) (Macica et al., 2003 and Wang et al., 1998). To unmask phosphorylated (inactive) Kv3 currents (Song et al., 2005), PKC antagonists were employed to block basal PKC activity (Figure 6A). Ro31-7549 (100 nM) and GF109203X (1 μM) both inhibit conventional and novel PKC-δ and PKC-ɛ all isozymes (Song et al., 2005), allowing

full activity of endogenous Kv3 channels to be monitored. MNTB neurons now exhibited larger outward currents of 43 ± 6 nA (at +50 mV), and TEA (1 mM) blocked 73% of outward current, consistent with increased activity of Kv3 channels. Note that in the presence of TEA, the current magnitudes in the presence of PKC antagonists were similar to CBA WT+TEA (I/V curves are shown in Figures 6A and 6B), consistent with specific action of PKC on Kv3 channels. Activation of nitrergic signaling by a NO donor also increased outward currents; but importantly, TEA now had negligible actions in suppressing this potentiated outward current (Figure 6C), and the TEA-insensitive current is 3-fold larger than in control or PKC-blocked neurons. These data are consistent with a NO-dependent switch to dominance of a Kv2-delayed rectifier following sustained synaptic activity. Current clamp recordings confirmed that Kv3 made a major contribution to AP repolarization in naive MNTB neurons (Figure 6B, lower traces) because the AP half-width was increased by TEA. But after nitrergic activation, TEA had no effect on AP waveform ( Figure 6C, lower traces), consistent with lack of Kv3.