Figure 4.

Circadian rhythm parameters in low and high density cultures without supplement, and in low density cultures with high K⁺ (final 21 mM), high Ca²⁺ (final 3.6 mM), or 50% conditioned medium: percentage of rhythmic cells (A), brightness of cells (B), and (for rhythmic cells) period (C) and amplitude (D). Columns show average values ± SEM, and numerals within columns indicate number of cultures (A) or number of cells (B-D). Low, low density culture; K⁺, high K⁺, Ca²⁺, high Ca²⁺; CM, conditioned medium; ctl, control; ns, not significant; *p < 0.05; **p < 0.01 (ANOVA followed by Dunnett’s test). Significance levels for comparisons to low density cultures are shown in black, and comparisons to high density cultures in gray. At right (E), representative PER2::LUC bioluminescence patterns of cultured fibroblasts at low density with regular medium (top), at low density with conditioned medium (middle), and at high density (bottom).