Fig. 2.

Permanent cell cycle withdrawal and reversible G₁ arrest differentially affect cyclin D-associated kinase activity. In the top panel, OPs were cultured for 2 d in PDGF and then for 3 d in N1 plus 0.5% FBS medium or N1 plus T3 (100 ng/ml) hormone medium. In the bottom panel, cells were cultured for 2 d with 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). Cyclin D-associated kinase activity was determined after immunoprecipitation of 100 μg of total cellular protein extracts with anti-cyclin D antibodies and by using pRb as a substrate. Data were obtained after PhosphorImager analysis of the autoradiographs and are expressed as percentage of cyclin D-associated kinase activity found in cells cultured in PDGF. Averages of four separate experiments are shown. Error bars are SEM. *p < 0.05 versus PDGF (Student's t test).