Figure 2. Time course of endogenous NO-induced cGMP production at three O₂ concentrations.

(a) Cells were treated overnight with tetracycline (5 ng/ml), and a time course of NO-activated cGMP production was measured inside hypoxic chambers at three O₂ concentrations (21, 3 and 1.5% O₂). Maximal cGMP accumulation was detected 3 min after L-arginine (1 mM) administration. (b) Time course as in (a), but in the presence of IBMX (0.5 mM), an inhibitor of endogenous PDEs. Values are the means and S.D. for at least three independent experiments.