Circadian Dynamics of Cytosolic and Nuclear Ca2+ in Single Suprachiasmatic Nucleus Neurons

Abstract

Intracellular free Ca(2+) regulates diverse cellular processes, including membrane potential, neurotransmitter release, and gene expression. To examine the cellular mechanisms underlying the generation of circadian rhythms, nucleus-targeted and untargeted cDNAs encoding a Ca(2+)-sensitive fluorescent protein (cameleon) were transfected into organotypic cultures of mouse suprachiasmatic nucleus (SCN), the primary circadian pacemaker. Circadian rhythms in cytosolic but not nuclear Ca(2+) concentration were observed in SCN neurons. The cytosolic Ca(2+) rhythm period matched the circadian multiple-unit-activity (MUA)-rhythm period monitored using a multiple-electrode array, with a mean advance in phase of 4 hr. Tetrodotoxin blocked MUA, but not Ca(2+) rhythms, while ryanodine damped both Ca(2+) and MUA rhythms. These results demonstrate cytosolic Ca(2+) rhythms regulated by the release of Ca(2+) from ryanodine-sensitive stores in SCN neurons.

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

“…In a previous study, Ikeda et al (2003) demonstrated a TTXresistant circadian rhythm in cytosolic, but not nuclear, Ca 2ϩ concentration. These data are not necessarily at variance with our findings.…”

Genetically Encoded Fluorescent Indicators for Organellar Calcium Imaging

“…1), nuclear GECIs can be generated by attaching nuclear localization sequences to cytosolic GECIs. Actually, a variety of fluorescent indicators including FRET-type and single-FP-type GECIs have been used to visualize nuclear Ca 2þ signals, showing that the nuclear Ca 2þ signal is mostly synchronized with the cytosolic Ca 2þ signal (9,16,19,21,(54)(55)(56)(57).…”

Circadian Regulation and Function of Voltage-Dependent Calcium Channels in the Suprachiasmatic Nucleus

“…In mammals, there is increasing evidence that voltage-dependent calcium channels (VDCCs) may contribute to the clock function of SCN cells. SCN neurons exhibit the following: circadian rhythms of intracellular calcium concentration (Colwell, 2000;Ikeda et al, 2003), all major subtypes of VDCC currents (Cloues and Sather, 2003), and oscillations in the calcium currents generated by some VDCC subtypes (Pennartz et al, 2002;Kim et al, 2005). VDCCs have also been implicated in SCN intercellular communication, because treatment with cadmium, a nonselective calcium channel antagonist (Cloues and Sather, 2003), disrupts the synchronization of circadian rhythms in firing rate be-tween synaptically paired SCN neurons (Shirakawa et al, 2000).…”