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

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.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.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.In most species, numerous physiological processes are regulated by a timing system associated with the rotational movement (~24 h) of our planet. The circadian rhythms are anticipatory adjustments of metabolic and behavioral processes elicited by daily environmental fluctuations [1]. At the cellular level, circadian rhythms are maintained by a system of interlocking positive (CLOCK and BMAL) and negative (PER and CRY) feedback loops of transcription/translation driven by the core clock genes [2]. The circadian clock, in turn, communicates rhythmicity to a number of output pathways by controlling E-box-associated gene expression and the metabolic status of the cell [3].Environmental factors that provide entraining cues (zeitgebers) communicate the passage of time to cellular circadian clocks. Two well-recognized zeitgebers are the alternating light/dark cycle and food availability. Photic stimuli entrain the main mammalian pacemaker, the supr