Acute Knockdown of Kv4.1 Regulates Repetitive Firing Rates and Clock Gene Expression in the Suprachiasmatic Nucleus and Daily Rhythms in Locomotor Behavior

Abstract

Rapidly activating and inactivating A-type K+ currents (IA) encoded by Kv4.2 and Kv4.3 pore-forming (α) subunits of the Kv4 subfamily are key regulators of neuronal excitability. Previous studies have suggested a role for Kv4.1 α-subunits in regulating the firing properties of mouse suprachiasmatic nucleus (SCN) neurons. To test this, we utilized an RNA-interference strategy to knockdown Kv4.1, acutely and selectively, in the SCN. Current-clamp recordings revealed that the in vivo knockdown of Kv4.1 significantly (p < 0.0001) increased mean ± SEM repetitive firing rates in SCN neurons during the day (6.4 ± 0.5 Hz) and at night (4.3 ± 0.6 Hz), compared with nontargeted shRNA-expressing SCN neurons (day: 3.1 ± 0.5 Hz; night: 1.6 ± 0.3 Hz). IA was also significantly (p < 0.05) reduced in Kv4.1-targeted shRNA-expressing SCN neurons (day: 80.3 ± 11.8 pA/pF; night: 55.3 ± 7.7 pA/pF), compared with nontargeted shRNA-expressing (day: 121.7 ± 10.2 pA/pF; night: 120.6 ± 16.5 pA/pF) SCN neurons. The magnitude of the effect of Kv4.1-targeted shRNA expression on firing rates and IA was larger at night. In addition, Kv4.1-targeted shRNA expression significantly (p < 0.001) increased mean ± SEM nighttime input resistance (Rin; 2256 ± 166 MΩ), compared to nontargeted shRNA-expressing SCN neurons (1143 ± 93 MΩ). Additional experiments revealed that acute knockdown of Kv4.1 significantly (p < 0.01) shortened, by ∼0.5 h, the circadian period of spontaneous electrical activity, clock gene expression and locomotor activity demonstrating a physiological role for Kv4.1-encoded IA channels in regulating circadian rhythms in neuronal excitability and behavior.

Shaw and Shal voltage‐gated potassium channels mediate circadian changes in Drosophila clock neuron excitability

“…Its knock‐down had a greater effect at night (Hermanstyne et al . ), with similar effects reported in Drosophila (Feng et al . ).…”

“…; Hermanstyne et al . ). On the other hand, Shaw regulates the firing rate in a range of Drosophila neurons including clock neurons probably by a separate mechanism to Shal, via controlling the resting membrane potential (Tsunoda & Salkoff, ; Hodge et al .…”

“…; Hermanstyne et al . ). Kv4.2 (Shal) and Kv1.4 (Shaker) are expressed in the SCN and loss of function mutants disrupt the clock neuron neuronal firing, circadian behaviour and circadian period of PER2 expression, reiterating the importance and interdependence of the rhythmic changes in membrane excitability of clock neurons and the molecular clock (Granados‐Fuentes et al .…”

“…, ; Hermanstyne et al . ). Additionally, block of Shal function by a dominant negative (DN) transgene in Drosophila has been associated with clock neuronal hyperexcitation, preferentially increasing clock neuron firing rates around ZT13 when rhythmic change in resting membrane potential and firing rate are low, disrupting PDF signalling to DN1 clock neurons (Feng et al .…”

“…Shal/Kv4 is an A-type channel regulating neuronal firing (Gasque et al 2005), including SCN firing rates, and affects circadian rhythms with knock-down having greater effect at night (Itri et al 2010;Hermanstyne et al 2017). Kv4.2 (Shal) and Kv1.4 (Shaker) are expressed in the SCN and loss of function mutants disrupt the clock neuron neuronal firing, circadian behaviour and circadian period of PER2 expression, reiterating the importance and interdependence of the rhythmic changes in membrane excitability of clock neurons and the molecular clock (Granados-Fuentes et al 2012Hermanstyne et al 2017). Additionally, block of Shal function by a dominant negative (DN) transgene in Drosophila has been associated with clock neuronal hyperexcitation, preferentially increasing clock neuron firing rates around ZT13 when rhythmic change in resting membrane potential and firing rate are low, disrupting PDF signalling to DN1 clock neurons (Feng et al 2018).…”