Ryanodine‐sensitive intracellular Ca²⁺ channels are involved in the output from the SCN circadian clock

Abstract

The suprachiasmatic nuclei (SCN) contain the major circadian clock responsible for generation of circadian rhythms in mammals. The time measured by the molecular circadian clock must eventually be translated into a neuronal firing rate pattern to transmit a meaningful signal to other tissues and organs in the animal. Previous observations suggest that circadian modulation of ryanodine receptors (RyR) is a key element of the output pathway from the molecular circadian clock. To directly test this hypothesis, we studied the effects of RyR activation and inhibition on real time expression of PERIOD2::LUCIFERASE, intracellular calcium levels and spontaneous firing frequency in mouse SCN neurons. Furthermore, we determined whether the RyR-2 mRNA is expressed with a daily variation in SCN neurons. We provide evidence that pharmacological manipulation of RyR in mice SCN neurons alters the free [Ca 2+ ] i in the cytoplasm and the spontaneous firing without affecting the molecular clock mechanism. Our data also show a daily variation in RyR-2 mRNA from single mouse SCN neurons with highest levels during the day. Together, these results confirm the hypothesis that RyR-2 is a key element of the circadian clock output from SCN neurons.

Neuronal oscillations on an ultra‐slow timescale: daily rhythms in electrical activity and gene expression in the mammalian master circadian clockwork

“…Interestingly, pharmacological disruption of RyR function abolishes circadian rhythms in [Ca 2+ ] i level, electrical activity and behaviour (Ikeda et al., ; Mercado et al., ), suggesting that this is a key link between the molecular and electrical oscillations in SCN neurons. Indeed, members of the molecular clock, Bmal1 and Cry1 , interact to modulate the activity of the RyR2 transcription (Pfeffer et al., ; Ikeda & Ikeda, ), while pharmacological activation of the RyRs causes excitation in SCN neurons (Aguilar‐Roblero et al., , ). Together, this suggests that clock‐operated intracellular calcium store release contributes to the up‐state of SCN neurons during the day.…”

Diurnal properties of voltage‐gated Ca2+ currents in suprachiasmatic nucleus and roles in action potential firing

“…) and the night (Aguilar‐Roblero et al . ). Consistent with this, in some SCN neurons RyR inhibition caused a significant increase in firing rate during the night, via loss of activation of the BK Ca 2+ ‐activated K + current (Whitt et al .…”

“…; Aguilar‐Roblero et al . , ). However, the effects of RyR inhibitors on firing frequency can be heterogeneous between individual neurons (Diaz‐Munoz et al .…”

Blockade of RyRs in the ER Attenuates 6-OHDA-Induced Calcium Overload, Cellular Hypo-Excitability and Apoptosis in Dopaminergic Neurons

“…Studies have indicated that ER Ca 2+ release activated plasma membrane K + channels and contributed to the after hyperpolarizing potentials (AHPs), which then reduced neuronal activity in otic ganglion cells (Yoshizaki et al, 1995). Blocking RyRs/Ca 2+ -release channels with high doses of RY (100 μM) suppressed the rhythm in [Ca 2+ ] i and partially reduced the amplitude of the rhythm in the spike frequency of suprachiasmatic nucleus neurons in acute rat slices (Aguilar-Roblero et al, 2016). …”

“…RyRs activation by caffeine and RY has been shown to induce apoptosis in hamster ovary cells via the depletion of intracellular Ca 2+ (Pan et al, 2000), but RyRs inhibition for 24 h did not induce death in MIN6 cells (Luciani et al, 2009). Inhibiting IP 3 Rs, which disturbs constitutive Ca 2+ transfer to the mitochondria, influences ATP production and leads to the activation of AMP-activated kinase (AMPK) and a subsequent increase in basal autophagic flux as a compensatory pro-survival response (Aguilar-Roblero et al, 2016). However, chronic IP 3 Rs inhibition with 2-aminoethoxydiphenyl borate and Xes decreased the survival of DA neurons in midbrain cultures (Missiaen et al, 1996).…”