Chronic inhibition of endoplasmic reticulum calcium-release channels and calcium-ATPase lengthens the period of hepatic clock gene Per1

BACKGROUND The role played by calcium as a regulator of circadian rhythms is not well understood. The effect of the pharmacological inhibition of the ryanodine receptor (RyR), inositol 1,4,5-trisphosphate receptor (IP3R), and endoplasmic-reticulum Ca2+-ATPase (SERCA), as well as the intracellular Ca2+-chelator BAPTA-AM was explored on the 24-h rhythmicity of the liver-clock protein PER1 in an experimental model of circadian synchronization by light and restricted-feeding schedules. METHODS Liver explants from Period1-luciferase (Per1-luc) transgenic rats with either free food access or with a restricted meal schedule were treated for several days with drugs to inhibit the activity of IP3Rs (2-APB), RyRs (ryanodine), or SERCA (thapsigargin) as well as to suppress intracellular calcium fluctuations (BAPTA-AM). The period of Per1-luc expression was measured during and after drug administration. RESULTS Liver explants from rats fed ad libitum showed a lengthened period in response to all the drugs tested. The pharmacological treatments of the explants from meal-entrained rats induced the same pattern, with the exception of the ryanodine treatment which, unexpectedly, did not modify the Per1-luc period. All effects associated with drug application were reversed after washout, indicating that none of the pharmacological treatments was toxic to the liver cultures. CONCLUSIONS Our data suggest that Ca2+ mobilized from internal deposits modulates the molecular circadian clock in the liver of rats entrained by light and by restricted meal access.