(A) Concentration-response curve for the inhibitory effect of thrombin on Epo (0.5 U/mL)-dependent DNA synthesis. Data points give mean values ±SEM of three separate cultures from one batch of cells. The curve represents a nonlinear least square fit to the data points. (Inset) Reversal of thrombin’s (throm, 2 U/mL) inhibition of Epo-stimulated DNA synthesis by hirudin (hir, 2 U/mL). (B) Time dependence of the inhibitory effect of thrombin on Epo-simulated DNA synthesis. At time zero (end of starvation period) Epo (0.5 U/mL) or Epo together with thrombin (2 U/mL) were each added to 16 cell cultures. A first group of four cultures from each condition received 3H-thymidine at time zero, a second group after 5 hours, a third after 10 hours, and the last group after 15 hours. Thymidine incorporation was always measured 5 hours later, except for the last group, which was exposed to 3H-thymidine for 10 hours. Data points give the mean ±SEM of four cultures.
