BK calcium-activated potassium channels regulate circadian behavioral rhythms and pacemaker output

Area of Science:

• Neuroscience
• Chronobiology
• Molecular Biology

Background:

• The suprachiasmatic nucleus (SCN) governs mammalian circadian timing through daily oscillations in spontaneous firing rate (SFR).
• The specific ionic conductances controlling SCN SFR and their link to behavioral rhythms remain unclear.
• Understanding SCN function is crucial for deciphering circadian rhythm regulation.

Purpose of the Study:

• To investigate the role of the large conductance Ca(2+)-activated K(+) channel (BK) in regulating SCN spontaneous firing rate (SFR).
• To determine the impact of BK channel dysfunction on circadian behavioral rhythms.
• To elucidate the contribution of BK channels to SCN pacemaker output.

Main Methods:

• Utilized BK channel-null mice (Kcnma1(-/-)) to assess the channel's function in vivo.
• Measured spontaneous firing rates (SFR) in SCN neurons of wild-type and mutant mice.
• Evaluated circadian behavioral amplitudes in BK channel-null mice.
• Assessed the expression of core clock genes (e.g., Arntl/Bmal1) in mutant mice.

Main Results:

• Daily expression of BK channels in the SCN is regulated by the intrinsic circadian clock.
• BK channel-null mice exhibited elevated SCN neuronal SFR specifically during the night.
• Kcnma1(-/-) mice displayed significantly reduced amplitudes in multiple SCN-timed behaviors.
• Clock gene expression, including Arntl (Bmal1), remained normal in BK channel-null mice.

Conclusions:

• BK channels are critical regulators of SCN neuronal SFR.
• The SCN pacemaker modulates circadian behavioral rhythms via SFR.
• BK channels are integral to SCN pacemaker output, not intrinsic timekeeping.
• This study implicates BK channels in the fundamental mechanisms of circadian timing.