title: Circadian modulation of calcium levels in cells in the suprachiasmatic nucleus.
abstract: There is reason to believe that resting free calcium concentration [Ca2+]i in neurons in the suprachiasmatic nucleus (SCN) may vary with the circadian cycle. In order to start to examine this hypothesis, optical techniques were utilized to estimate resting Ca2+ levels in SCN cells in a rat brain slice preparation. [Ca2+]i measured from the soma was significantly higher in the day than in the night. Animals from a reversed light-dark cycle were used to confirm that the phase of the rhythm was determined by the prior light-dark cycle. The rhythm in Ca2+ levels continued to be expressed in tissue collected from animals maintained in constant darkness, thus confirming the endogenous nature of this variation. Interestingly, the rhythm in Ca2+ levels was not observed when animals were housed in constant light. Finally, the rhythm in Ca2+ levels was prevented when slices were exposed to tetrodotoxin (TTX), a blocker of voltage-sensitive sodium channels. Similar results were obtained with the voltage-sensitive Ca2+ channel blocker methoxyverapamil. These observations suggest a critical role for membrane events in driving the observed rhythm in Ca2+. Conceptually, this rhythm can be thought of as an output of the circadian oscillator. Because [Ca2+]i is known to play a critical role in many cellular processes, the presence of this rhythm is likely to have many implications for the cell biology of SCN neurons.
authors.affiliation: Mental Retardation Research Center, Department of Psychiatry and Biobehavioural Sciences, University of California-Los Angeles, 760 Westwood Plaza, Los Angeles, CA 90024-1759, USA. ccolwell@mednet.ucla.edu
authors.forename: C S
authors.initials: CS
authors.lastname: Colwell
mesh_terms: D000200:Action Potentials; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D005711:Gallopamil / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D008027:Light; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D009419:Nerve Tissue Proteins / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000502:physiology* / Q000528:radiation effects; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D009419:Nerve Tissue Proteins; D015222:Sodium Channels; D005711:Gallopamil; D013779:Tetrodotoxin