IA Channels Encoded by Kv1.4 and Kv4.2 Regulate Neuronal Firing in the Suprachiasmatic Nucleus and Circadian Rhythms in Locomotor Activity

Abstract

Neurons in the suprachiasmatic nucleus (SCN) display coordinated circadian changes in electrical activity that are critical for daily rhythms in physiology, metabolism, and behavior. SCN neurons depolarize spontaneously and fire repetitively during the day and hyperpolarize, drastically reducing firing rates, at night. To explore the hypothesis that rapidly activating and inactivating A-type (I A ) voltage-gated K ϩ (Kv) channels, which are also active at subthreshold membrane potentials, are critical regulators of the excitability of SCN neurons, we examined locomotor activity and SCN firing in mice lacking Kv1.4 (Kv1.4

IA Channels Encoded by Kv1.4 and Kv4.2 Regulate Circadian Period of PER2 Expression in the Suprachiasmatic Nucleus

“…As illustrated in Figure 1, the mean ± SEM periods of PER2::LUC expression in Kv1.4 −/− Per2 Luc (24.2 ± 0.1 h) and Kv4.2 −/− Per2 Luc (24.4 ± 0.2 h) SCN explants were significantly ( p < 0.001 1-way ANOVA) shorter than in Per2 Luc (25.0 ± 0.1) and Kv4.3 −/− Per2 Luc SCN explants (25.3 ± 0.1). The magnitude (~0.5 h) of the differences in the periods of PER2::LUC expression in the Kv1.4 −/− Per2 Luc and the Kv4.2 −/− Per2 Luc , compared with the Per2 Luc and the Kv4.3 −/− Per2 Luc , SCN explants is similar to the (~0.5 h) shift in the period of locomotor behavior reported for mice lacking either Kv1.4 or Kv4.2 (Granados-Fuentes et al, 2012). SCN explants prepared from mice ( Kv1.4 −/− / Kv4.2 −/− Per2 Luc ) lacking both Kv1.4 and Kv4.2 had PER2::LUC rhythms with a mean ± SEM circadian period (24.6 ± 0.1 h) that is also significantly ( p < 0.001 1-way ANOVA) shorter than in the explants from Per2 Luc (25.0 ± 0.1 h) mice (Fig.…”

“…Rapidly activating and rapidly inactivating Kv currents, I A , were isolated using a 2-step voltage-clamp protocol, as previously described (Norris and Nerbonne, 2010; Granados-Fuentes et al, 2012). Briefly, whole-cell Kv currents in each cell, evoked in response to 4-s depolarizing voltage steps to potentials between −40 and +30 mV (in 10-mV increments) from a holding potential of −70 mV, were first recorded.…”

“…Currents were measured again with a prepulse paradigm that included a brief (60-ms) step to −10 mV before the 4-s depolarizing voltage steps to potentials between −40 and +30 mV (in 10-mV increments). Off-line subtraction of the Kv currents recorded with the prepulse paradigm from the currents evoked without the prepulse were performed to isolate I A (Norris and Nerbonne, 2010; Granados-Fuentes et al, 2012). …”

“…In recent studies focused on exploring the roles of subthreshold, voltage-gated A-type K + channels in mediating the daily rhythms in the resting membrane potentials and the repetitive firing rates of SCN neurons, we found that the firing rates are increased in SCN neurons in mice deficient for either Kcna4 ( Kv1.4 −/− ) or Kcnd2 ( Kv4.2 −/− ), but not Kcnd3 ( Kv4.3 −/− ), which encode the pore-forming (α) subunits of subthreshold, rapidly activating and inactivating A-type neuronal K + currents (I A ) (Granados-Fuentes et al, 2012). In addition, Kv1.4 −/− and Kv4.2 −/− mice, but not Kv4.3 −/− mice, have shortened (by approximately 0.5 h) circadian periods of locomotor activity and start their daily activity 0.5 h earlier than wild-type (WT) mice (Granados-Fuentes et al, 2012).…”

“…In addition, Kv1.4 −/− and Kv4.2 −/− mice, but not Kv4.3 −/− mice, have shortened (by approximately 0.5 h) circadian periods of locomotor activity and start their daily activity 0.5 h earlier than wild-type (WT) mice (Granados-Fuentes et al, 2012). The experiments here were designed to test directly the hypothesis that the loss of Kv1.4- or Kv4.2-encoded I A channels also modifies circadian rhythms in the protein expression levels of the clock gene, PERIOD2 (PER2), taking advantage of the availability of ( Per2 Luc ) mice generated with a PER2::LUCIFERASE (PER2::LUC) reporter construct replacing the endogenous mouse Per2 locus (Yoo et al, 2004).…”