Figure 5.

Dose response of the selective PDE8 inhibitor PF-04957325 on isoproterenol- or prostaglandin E₂ (PGE₂)-stimulated cAMP dynamics in live HASM cells. (A) Representative cAMP difference detector in situ sensor fluorescence decay curves (F/F₀) are shown for minimally effective concentrations of isoproterenol (1 nM) or PGE₂ (3 nM) with and without 10 μM SQ22536 to suppress basal adenylyl cyclase activity. Various concentrations of PF-04957325 were then added to these same conditions. Representative decay curves are shown in the presence of 10 μM SQ22536 plus either (B) 1 nM isoproterenol or (C) 3 nM PGE₂. PF-04957325 was tested at concentrations from 10⁻¹¹ M (lightest circle) to 10⁻⁶ M (black circle). (D) Kinetic rate constants (k) from one-phase decay analysis (with a shared constrained plateau) were calculated for each dose of PF-04957325, and the pooled data from multiple experiments is shown. Each bar represents the mean ± SEM (n = 5 experiments). *P < 0.05 by paired t test as compared with isoproterenol.