Fig. 2.

Picrotoxin shortens period by advancing accumulation of PER2 protein without altering casein kinase 1ε (CK1ε) activity. A: PER2::LUC rhythms of single SCN cells under baseline (black) and picrotoxin (gray) conditions were phase-aligned, averaged, and normalized to peak (means ± SE, n = 50). Picrotoxin advances the accumulation of PER2 protein on subsequent days (3.7 h) but does not alter rhythm half-width. B: CK1ε kinase activity was assessed by the rate of phosphate incorporation of PER2 peptide. Picrotoxin (100 μM) and picrotoxinin (100 μM) did not alter the rate of phosphoincorporation relative to vehicle (DMSO; P = 0.97), however, a specific antagonist of CK1ε (SP600125) was effective (P < 0.001).