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The Journal of Neuroscience, August 17, 2005, 25(33):7682-7686; doi:10.1523/JNEUROSCI.2211-05.2005

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BRIEF COMMUNICATION
A Calcium Flux Is Required for Circadian Rhythm Generation in Mammalian Pacemaker Neurons

Gabriella B. Lundkvist,¹ Yongho Kwak,¹ Erin K. Davis,¹ Hajime Tei,² and Gene D. Block¹

¹Center for Biological Timing, Department of Biology, University of Virginia, Charlottesville, Virginia 22903, and ²Research Group of Chronogenomics, Mitsubishi Kagaku Institute of Life Sciences, Machida, Tokyo 194-8511, Japan

Generation of mammalian circadian rhythms involves molecular transcriptional and translational feedback loops. It is not clear how membrane events interact with the intracellular molecular clock or whether membrane activities are involved in the actual generation of the circadian rhythm. We examined the role of membrane potential and calcium (Ca²⁺) influx in the expression of the circadian rhythm of the clock gene Period 1 (Per1) within the rat suprachiasmatic nucleus (SCN), the master pacemaker controlling circadian rhythmicity. Membrane hyperpolarization, caused by lowering the extracellular concentration of potassium or blocking Ca²⁺ influx in SCN cultures by lowering [Ca²⁺], reversibly abolished the rhythmic expression of Per1. In addition, the amplitude of Per1 expression was markedly decreased by voltage-gated Ca²⁺ channel antagonists. A similar result was observed for mouse Per1 and PER2. Together, these results strongly suggest that a transmembrane Ca²⁺ flux is necessary for sustained molecular rhythmicity in the SCN. We propose that periodic Ca²⁺ influx, resulting from circadian variations in membrane potential, is a critical process for circadian pacemaker function.

Key words: circadian rhythm; calcium; potassium; suprachiasmatic nucleus; Period 1; PERIOD 2

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Received Jan 30, 2005; revised July 3, 2005; accepted July 5, 2005.

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