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. 2008 Oct 14;6(10):1–18. doi: 10.1371/journal.pbio.0060249

Figure 10. GABA Acts Posttranscriptionally through Membrane Polarization and Casein Kinase.

Figure 10

(A) Shown are relative mRNA abundance of Per1, Per2, Clock, and Bmal1 in retinal explants 8 h after treatment with 3 mM GABA (black) or vehicle (grey) started at the beginning of the third circadian cycle. Clock gene mRNA levels were normalized to the mRNA levels of GAPDH. The average mRNA levels of vehicle-treated samples were set to 1.0. Data are presented as means ± SEM (n = 4). GABA did not significantly change the transcript levels of Per2 and Clock, while significantly increased the transcript levels of Per1 and Bmal1. A single asterisk (*)indicates p < 0.05; double asterisks (**) indicate p < 0.01; Student's t-test.

(B) GABA (1 mM) greatly suppressed retinal PER2::LUC rhythms.

(C) Depolarization with elevated K+ (4 mM) partially blocked the inhibitory effect of GABA (1 mM) on retinal PER2::LUC rhythms.

(D) Prolonged application of KCl (4 mM) modestly increased rhythmic PER2::LUC amplitudes.

(E) Inhibition of casein kinase activity with CKI-7 (50 μM) partially rescued the inhibitory action of 1 mM GABA on retinal PER2::LUC rhythms.

(F) KCl (4 mM) and CKI-7 (50 μM) greatly rescued the inhibitory action of GABA (1 mM) on retinal PER2::LUC rhythms when they were co-applied with GABA.

(G) When CKI-7 (50 μM) was applied alone, it lengthened the period of retinal PER2::LUC rhythms.

Bars in (B–G) indicate the duration of treatment.