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 (IP(3)R), and endoplasmic-reticulum Ca(2+)-ATPase (SERCA), as well as the intracellular Ca(2+)-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 IP(3)Rs (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 Ca(2+ )mobilized from internal deposits modulates the molecular circadian clock in the liver of rats entrained by light and by restricted meal access.