The role of inositol trisphosphate-induced Ca2+ release from IP3-receptor in the rat suprachiasmatic nucleus on circadian entrainment mechanism.

Synchronization between the environmental lighting cycle and the circadian clock in the suprachiasmatic nucleus (SCN) is correlated with Ca2+ increase. The mechanism underlying the increase of Ca2+ and its relation to clock resetting are unknown. To address these issues, we examined the possibility whether inositol 1,4,5-trisphosphate receptor (IP3-R), which regulate intracellular Ca2+, was involved in the circadian rhythm component of the rat SCN. A novel IP3-induced Ca2+ release modulator, 2-amino-ethoxy diphenylborate (2APB), blocked optic nerve stimulation-induced neuronal field potentials in the SCN. Furthermore, glutamate-induced phase delay of the circadian firing pattern in the SCN was also blocked completely by 2APB in vitro. Together, these data suggest the possibility that IP3-induced Ca2+ release through IP3-R plays a role in the entrainment of the mammalian circadian clock, the SCN.