Table 1.

Expression of cyclins and cyclin-dependent kinases in oligodendrocyte progenitor cells changes during development in culture and after treatment with agents that cause cell cycle arrest in G1 phase

Relative protein levels (% of PDGF-treated controls)
Culture conditions	Cell cycle withdrawal		Cell cycle arrest
	N1	T3	iso	kai	TEA	ver
Cyclin D	40  ± 10*	41  ± 8*	166  ± 21*	198  ± 8.01-168	144  ± 12*	177  ± 9.2*
Cyclin E	15  ± 41-160	44  ± 161-165	117  ± 9.9	104  ± 2.6	108  ± 20	114  ± 16
Cdk2	78  ± 6.7*	69  ± 7.8*	112  ± 5.0	98  ± 5.3	81  ± 9.5	94  ± 6.0
Cdk4	79  ± 8.1*	65  ± 4.21-165	106  ± 2.9	106  ± 9.5	80  ± 15	90  ± 2.5
Cdk6	58  ± 15*	20  ± 7.91-165	105  ± 6.5	125  ± 20	121  ± 18	127  ± 25

OP cells were cultured under conditions that caused permanent cell cycle withdrawal (2 d in PDGF, followed by 3 d in N1 plus 0.5% FBS medium or N1 plus T3 hormone medium) or reversible cell cycle arrest in G1 phase [2 d in PDGF, in the presence or in the absence of the β-AR agonist isoproterenol (iso; 50 μm), the GluR agonist kainate (kai; 100 μm), the K⁺ channel blocker TEA (5 mm), or the Na⁺ channel opener veratridine (ver; 30 μm)]. Western blot analysis was performed by loading 20–25 μg of cell lysates for each sample. Values were determined by densitometric analysis of autoradiographs from Western blots and are expressed as ratios of samples treated with PDGF alone. The mean ± SEM of three to five separate experiments is shown for each treatment;

^*p < 0.05,

F1-160: p < 0.01,

F1-165: p< 0.005, and

F1-168: p < 0.001 compared with PDGF-treated cells (Student's t test).