Altered effect of BAY K 8644 after exposure of the rat aorta to IBMX or Db cAMP.

The development of isometric tension of aortic rings from rats was tested after cumulative administration of BAY K 8644 before and after exposure of the aortic preparations for 15 or 60 minutes to IBMX (10(-4) M) or Db cAMP (3.10(-4) M). BAY K 8644 exhibits dose-dependent contractions of those aortic rings which have not been exposed or have been exposed for only 15 minutes to IBMX or Db cAMP. BAY K 8644 application, after an exposure time of 60 minutes of the aortic rings to either IBMX or Db cAMP, resulted in a dose-dependent relaxation. This relaxing effect is counteracted by elevation of KCl (15 mM) in bath solution but was not changed by norepinephrine. The results indicate that long time exposure of the aortic rings to compounds capable of elevating intracellular cAMP level might induce changes of Ca channel gating.