Circadian modulation of calcium levels in cells in the suprachiasmatic nucleus

Eur J Neurosci. 2000 Feb;12(2):571-6. doi: 10.1046/j.1460-9568.2000.00939.x.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Action Potentials
  • Animals
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels, N-Type / drug effects
  • Calcium Channels, N-Type / physiology
  • Calcium Signaling / physiology*
  • Circadian Rhythm / physiology*
  • Darkness
  • Gallopamil / pharmacology
  • Ion Channel Gating / drug effects
  • Ion Transport / drug effects
  • Light
  • Microscopy, Fluorescence
  • Microscopy, Video
  • Nerve Tissue Proteins / drug effects
  • Nerve Tissue Proteins / physiology
  • Neurons / cytology
  • Neurons / physiology
  • Patch-Clamp Techniques
  • Rats
  • Rats, Sprague-Dawley
  • Sodium Channels / drug effects
  • Sodium Channels / physiology
  • Suprachiasmatic Nucleus / physiology*
  • Suprachiasmatic Nucleus / radiation effects
  • Tetrodotoxin / pharmacology


  • Calcium Channel Blockers
  • Calcium Channels, N-Type
  • Nerve Tissue Proteins
  • Sodium Channels
  • Gallopamil
  • Tetrodotoxin