Protein kinase C inhibition and activation phase advances the hamster circadian clock.

The mammalian circadian clock is located in the suprachiasmatic nuclei (SCN). Clock function can be detected by the measurement of the circadian change in cellular firing rate of SCN cells in vitro. We investigated the effects of protein kinase C (PKC) inhibition and activation on this rhythm of firing rate in hamster SCN neurons. PKC inhibition by chelerythrine chloride application phase advances the in vitro circadian rhythm during the late subjective night and early subjective morning, Zeitgeber time (ZT) 20-24 and ZT 0-4. No effect of PKC inhibition on clock phase was seen during ZT 6-18. Activation of PKC via phorbol 12-myristate 13-acetate (PMA) phase advanced the clock at all phases tested. Thus, at some circadian phases both inhibition and activation of PKC can advance circadian rhythms.