Fig. 2.

The effects of isoproterenol, Fen, and fenoterol derivatives on cell growth are cell type specific. A and B, serum-starved HepG2 cells were incubated with vehicle or the indicated concentrations of Iso, Fen, or (R,R′)-aminofenoterol (NH₂-fen) (A) or MNF (B) for 24 h, and the levels of [³H]thymidine incorporation were measured; see Materials and Methods for experimental details. Representative concentration-response curves are shown. C, HepG2 cells in serum-depleted medium and 1321N1 cells in complete medium were treated with compounds at 1 μM for 24 h. D, HepG2 and 1321N1 cells were incubated without (SFM) or with serum (CM) in the presence of the indicated concentrations of Iso or Fen. Quantification of percentage change in [³H]thymidine incorporation versus control is expressed as means ± S.E. and represents results from two to six independent experiments, each performed in triplicate dishes. In most instances, error bars are smaller than the symbols.